Merge pull request #38 from achilleasa/refactor-console-and-tty-drivers

Refactor console and tty drivers

Makefile

@@ -170,6 +170,7 @@ lint: lint-check-deps
 		--deadline 300s \
 		--exclude 'return value not checked' \
 		--exclude 'possible misuse of unsafe.Pointer' \
+		--exclude 'x \^ 0 always equals x' \
 		./...
 
 lint-check-deps:

src/gopheros/device/driver.go

@@ -0,0 +1,19 @@
+package device
+
+import "gopheros/kernel"
+
+// Driver is an interface implemented by all drivers.
+type Driver interface {
+	// DriverName returns the name of the driver.
+	DriverName() string
+
+	// DriverVersion returns the driver version.
+	DriverVersion() (major uint16, minor uint16, patch uint16)
+
+	// DriverInit initializes the device driver.
+	DriverInit() *kernel.Error
+}
+
+// ProbeFn is a function that scans for the presence of a particular
+// piece of hardware and returns a driver for it.
+type ProbeFn func() Driver

src/gopheros/device/tty/device.go

@@ -0,0 +1,52 @@
+package tty
+
+import (
+	"gopheros/device/video/console"
+	"io"
+)
+
+const (
+	// DefaultScrollback defines the terminal scrollback in lines.
+	DefaultScrollback = 80
+
+	// DefaultTabWidth defines the number of spaces that tabs expand to.
+	DefaultTabWidth = 4
+)
+
+// State defines the supported terminal state values.
+type State uint8
+
+const (
+	// StateInactive marks the terminal as inactive. Any writes will be
+	// buffered and not synced to the attached console.
+	StateInactive State = iota
+
+	// StateActive marks the terminal as active. Any writes will be
+	// buffered and also synced to the attached console.
+	StateActive
+)
+
+// Device is implemented by objects that can be used as a terminal device.
+type Device interface {
+	io.Writer
+	io.ByteWriter
+
+	// AttachTo connects a TTY to a console instance.
+	AttachTo(console.Device)
+
+	// State returns the TTY's state.
+	State() State
+
+	// SetState updates the TTY's state.
+	SetState(State)
+
+	// CursorPosition returns the current cursor x,y coordinates. Both
+	// coordinates are 1-based (top-left corner has coordinates 1,1).
+	CursorPosition() (uint16, uint16)
+
+	// SetCursorPosition sets the current cursor position to (x,y). Both
+	// coordinates are 1-based (top-left corner has coordinates 1,1).
+	// Implementations are expected to clip the cursor position to their
+	// viewport.
+	SetCursorPosition(x, y uint16)
+}

src/gopheros/device/tty/probe.go

@@ -0,0 +1,11 @@
+package tty
+
+import "gopheros/device"
+
+// HWProbes returns a slice of device.ProbeFn that can be used by the hal
+// package to probe for TTY device hardware.
+func HWProbes() []device.ProbeFn {
+	return []device.ProbeFn{
+		probeForVT,
+	}
+}

src/gopheros/device/tty/vt.go

@@ -0,0 +1,265 @@
+package tty
+
+import (
+	"gopheros/device"
+	"gopheros/device/video/console"
+	"gopheros/kernel"
+	"io"
+)
+
+// VT implements a terminal supporting scrollback. The terminal interprets the
+// following special characters:
+//  - \r (carriage-return)
+//  - \n (line-feed)
+//  - \b (backspace)
+//  - \t (tab; expanded to tabWidth spaces)
+type VT struct {
+	cons console.Device
+
+	// Terminal dimensions
+	termWidth      uint16
+	termHeight     uint16
+	viewportWidth  uint16
+	viewportHeight uint16
+
+	// The number of additional lines of output that are buffered by the
+	// terminal to support scrolling up.
+	scrollback uint16
+
+	// The terminal contents. Each character occupies 3 bytes and uses the
+	// format: (ASCII char, fg, bg)
+	data []uint8
+
+	// Terminal state.
+	tabWidth         uint8
+	defaultFg, curFg uint8
+	defaultBg, curBg uint8
+	cursorX          uint16
+	cursorY          uint16
+	viewportY        uint16
+	dataOffset       uint
+	state            State
+}
+
+// NewVT creates a new virtual terminal device. The tabWidth parameter controls
+// tab expansion whereas the scrollback parameter defines the line count that
+// gets buffered by the terminal to provide scrolling beyond the console
+// height.
+func NewVT(tabWidth uint8, scrollback uint16) *VT {
+	return &VT{
+		tabWidth:   tabWidth,
+		scrollback: scrollback,
+		cursorX:    1,
+		cursorY:    1,
+	}
+}
+
+// AttachTo connects a TTY to a console instance.
+func (t *VT) AttachTo(cons console.Device) {
+	if cons == nil {
+		return
+	}
+
+	t.cons = cons
+	t.viewportWidth, t.viewportHeight = cons.Dimensions()
+	t.viewportY = 0
+	t.defaultFg, t.defaultBg = cons.DefaultColors()
+	t.curFg, t.curBg = t.defaultFg, t.defaultBg
+	t.termWidth, t.termHeight = t.viewportWidth, t.viewportHeight+t.scrollback
+	t.cursorX, t.cursorY = 1, 1
+
+	// Allocate space for the contents and fill it with empty characters
+	// using the default fg/bg colors for the attached console.
+	t.data = make([]uint8, t.termWidth*t.termHeight*3)
+	for i := 0; i < len(t.data); i += 3 {
+		t.data[i] = ' '
+		t.data[i+1] = t.defaultFg
+		t.data[i+2] = t.defaultBg
+	}
+}
+
+// State returns the TTY's state.
+func (t *VT) State() State {
+	return t.state
+}
+
+// SetState updates the TTY's state.
+func (t *VT) SetState(newState State) {
+	if t.state == newState {
+		return
+	}
+
+	t.state = newState
+
+	// If the terminal became active, update the console with its contents
+	if t.state == StateActive && t.cons != nil {
+		for y := uint16(1); y <= t.viewportHeight; y++ {
+			offset := (y - 1 + t.viewportY) * (t.viewportWidth * 3)
+			for x := uint16(1); x <= t.viewportWidth; x, offset = x+1, offset+3 {
+				t.cons.Write(t.data[offset], t.data[offset+1], t.data[offset+2], x, y)
+			}
+		}
+	}
+}
+
+// CursorPosition returns the current cursor position.
+func (t *VT) CursorPosition() (uint16, uint16) {
+	return t.cursorX, t.cursorY
+}
+
+// SetCursorPosition sets the current cursor position to (x,y).
+func (t *VT) SetCursorPosition(x, y uint16) {
+	if t.cons == nil {
+		return
+	}
+
+	if x < 1 {
+		x = 1
+	} else if x > t.viewportWidth {
+		x = t.viewportWidth
+	}
+
+	if y < 1 {
+		y = 1
+	} else if y > t.viewportHeight {
+		y = t.viewportHeight
+	}
+
+	t.cursorX, t.cursorY = x, y
+	t.updateDataOffset()
+}
+
+// Write implements io.Writer.
+func (t *VT) Write(data []byte) (int, error) {
+	for count, b := range data {
+		err := t.WriteByte(b)
+		if err != nil {
+			return count, err
+		}
+	}
+
+	return len(data), nil
+}
+
+// WriteByte implements io.ByteWriter.
+func (t *VT) WriteByte(b byte) error {
+	if t.cons == nil {
+		return io.ErrClosedPipe
+	}
+
+	switch b {
+	case '\r':
+		t.cr()
+	case '\n':
+		t.lf(true)
+	case '\b':
+		if t.cursorX > 1 {
+			t.SetCursorPosition(t.cursorX-1, t.cursorY)
+			t.doWrite(' ', false)
+		}
+	case '\t':
+		for i := uint8(0); i < t.tabWidth; i++ {
+			t.doWrite(' ', true)
+		}
+	default:
+		t.doWrite(b, true)
+	}
+
+	return nil
+}
+
+// doWrite writes the specified character together with the current fg/bg
+// attributes at the current data offset advancing the cursor position if
+// advanceCursor is true. If the terminal is active, then doWrite also writes
+// the character to the attached console.
+func (t *VT) doWrite(b byte, advanceCursor bool) {
+	if t.state == StateActive {
+		t.cons.Write(b, t.curFg, t.curBg, t.cursorX, t.cursorY)
+	}
+
+	t.data[t.dataOffset] = b
+	t.data[t.dataOffset+1] = t.curFg
+	t.data[t.dataOffset+2] = t.curBg
+
+	if advanceCursor {
+		// Advance x position and handle wrapping when the cursor reaches the
+		// end of the current line
+		t.dataOffset += 3
+		t.cursorX++
+		if t.cursorX > t.viewportWidth {
+			t.lf(true)
+		}
+	}
+}
+
+// cr resets the x coordinate of the terminal cursor to 0.
+func (t *VT) cr() {
+	t.cursorX = 1
+	t.updateDataOffset()
+}
+
+// lf advances the y coordinate of the terminal cursor by one line scrolling
+// the terminal contents if the end of the last terminal line is reached.
+func (t *VT) lf(withCR bool) {
+	if withCR {
+		t.cursorX = 1
+	}
+
+	switch {
+	// Cursor has not reached the end of the viewport
+	case t.cursorY+1 <= t.viewportHeight:
+		t.cursorY++
+	default:
+		// Check if the viewport can be scrolled down
+		if t.viewportY+t.viewportHeight < t.termHeight {
+			t.viewportY++
+		} else {
+			// We have reached the bottom of the terminal buffer.
+			// We need to scroll its contents up and clear the last line
+			var stride = int(t.viewportWidth * 3)
+			var startOffset = int(t.viewportY) * stride
+			var endOffset = int(t.viewportY+t.viewportHeight-1) * stride
+
+			for offset := startOffset; offset < endOffset; offset++ {
+				t.data[offset] = t.data[offset+stride]
+			}
+
+			for offset := endOffset; offset < endOffset+stride; offset += 3 {
+				t.data[offset+0] = ' '
+				t.data[offset+1] = t.defaultFg
+				t.data[offset+2] = t.defaultBg
+			}
+		}
+
+		// Sync console
+		if t.state == StateActive {
+			t.cons.Scroll(console.ScrollDirUp, 1)
+			t.cons.Fill(1, t.cursorY, t.termWidth, 1, t.defaultFg, t.defaultBg)
+		}
+	}
+
+	t.updateDataOffset()
+}
+
+// updateDataOffset calculates the offset in the data buffer taking into account
+// the cursor position and the viewportY value.
+func (t *VT) updateDataOffset() {
+	t.dataOffset = uint((t.viewportY+(t.cursorY-1))*(t.viewportWidth*3) + ((t.cursorX - 1) * 3))
+}
+
+// DriverName returns the name of this driver.
+func (t *VT) DriverName() string {
+	return "vt"
+}
+
+// DriverVersion returns the version of this driver.
+func (t *VT) DriverVersion() (uint16, uint16, uint16) {
+	return 0, 0, 1
+}
+
+// DriverInit initializes this driver.
+func (t *VT) DriverInit() *kernel.Error { return nil }
+
+func probeForVT() device.Driver {
+	return NewVT(DefaultTabWidth, DefaultScrollback)
+}

src/gopheros/device/tty/vt_test.go

@@ -0,0 +1,430 @@
+package tty
+
+import (
+	"gopheros/device"
+	"gopheros/device/video/console"
+	"image/color"
+	"io"
+	"reflect"
+	"testing"
+)
+
+func TestVtPosition(t *testing.T) {
+	specs := []struct {
+		inX, inY   uint16
+		expX, expY uint16
+	}{
+		{20, 20, 20, 20},
+		{100, 20, 80, 20},
+		{10, 200, 10, 25},
+		{10, 200, 10, 25},
+		{100, 100, 80, 25},
+	}
+
+	term := NewVT(4, 0)
+
+	// SetCursorPosition without an attached console is a no-op
+	term.SetCursorPosition(2, 2)
+
+	if curX, curY := term.CursorPosition(); curX != 1 || curY != 1 {
+		t.Fatalf("expected terminal initial position to be (1, 1); got (%d, %d)", curX, curY)
+	}
+
+	cons := newMockConsole(80, 25)
+	term.AttachTo(cons)
+
+	for specIndex, spec := range specs {
+		term.SetCursorPosition(spec.inX, spec.inY)
+		if x, y := term.CursorPosition(); x != spec.expX || y != spec.expY {
+			t.Errorf("[spec %d] expected setting position to (%d, %d) to update the position to (%d, %d); got (%d, %d)", specIndex, spec.inX, spec.inY, spec.expX, spec.expY, x, y)
+		}
+	}
+}
+
+func TestVtWrite(t *testing.T) {
+	t.Run("inactive terminal", func(t *testing.T) {
+		cons := newMockConsole(80, 25)
+
+		term := NewVT(4, 0)
+		if _, err := term.Write([]byte("foo")); err != io.ErrClosedPipe {
+			t.Fatal("expected calling Write on a terminal without an attached console to return ErrClosedPipe")
+		}
+
+		term.AttachTo(cons)
+
+		term.curFg = 2
+		term.curBg = 3
+
+		data := []byte("\b123\b4\t5\n67\r68")
+		count, err := term.Write(data)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if count != len(data) {
+			t.Fatalf("expected to write %d bytes; wrote %d", len(data), count)
+		}
+
+		if cons.bytesWritten != 0 {
+			t.Fatalf("expected writes not to be synced with console when terminal is inactive; %d bytes written", cons.bytesWritten)
+		}
+
+		specs := []struct {
+			x, y    uint16
+			expByte uint8
+		}{
+			{1, 1, '1'},
+			{2, 1, '2'},
+			{3, 1, '4'},
+			{8, 1, '5'}, // 2 + tabWidth + 1
+			{1, 2, '6'},
+			{2, 2, '8'},
+		}
+
+		for specIndex, spec := range specs {
+			offset := ((spec.y - 1) * term.viewportWidth * 3) + ((spec.x - 1) * 3)
+			if term.data[offset] != spec.expByte {
+				t.Errorf("[spec %d] expected char at (%d, %d) to be %q; got %q", specIndex, spec.x, spec.y, spec.expByte, term.data[offset])
+			}
+
+			if term.data[offset+1] != term.curFg {
+				t.Errorf("[spec %d] expected fg attribute at (%d, %d) to be %d; got %d", specIndex, spec.x, spec.y, term.curFg, term.data[offset+1])
+			}
+
+			if term.data[offset+2] != term.curBg {
+				t.Errorf("[spec %d] expected bg attribute at (%d, %d) to be %d; got %d", specIndex, spec.x, spec.y, term.curBg, term.data[offset+2])
+			}
+		}
+	})
+
+	t.Run("active terminal", func(t *testing.T) {
+		cons := newMockConsole(80, 25)
+
+		term := NewVT(4, 0)
+		term.SetState(StateActive)
+		term.SetState(StateActive) // calling SetState with the same state is a no-op
+
+		if got := term.State(); got != StateActive {
+			t.Fatalf("expected terminal state to be %d; got %d", StateActive, got)
+		}
+
+		term.AttachTo(cons)
+
+		term.curFg = 2
+		term.curBg = 3
+
+		data := []byte("\b123\b4\t5\n67\r68")
+		term.Write(data)
+
+		if expCount := len(data); cons.bytesWritten != expCount {
+			t.Fatalf("expected writes to be synced with console when terminal is active. %d bytes written; expected %d", cons.bytesWritten, expCount)
+		}
+
+		specs := []struct {
+			x, y    uint16
+			expByte uint8
+		}{
+			{1, 1, '1'},
+			{2, 1, '2'},
+			{3, 1, '4'},
+			{8, 1, '5'}, // 2 + tabWidth + 1
+			{1, 2, '6'},
+			{2, 2, '8'},
+		}
+
+		for specIndex, spec := range specs {
+			offset := ((spec.y - 1) * cons.width) + (spec.x - 1)
+			if cons.chars[offset] != spec.expByte {
+				t.Errorf("[spec %d] expected console char at (%d, %d) to be %q; got %q", specIndex, spec.x, spec.y, spec.expByte, cons.chars[offset])
+			}
+
+			if cons.fgAttrs[offset] != term.curFg {
+				t.Errorf("[spec %d] expected console fg attribute at (%d, %d) to be %d; got %d", specIndex, spec.x, spec.y, term.curFg, cons.fgAttrs[offset])
+			}
+
+			if cons.bgAttrs[offset] != term.curBg {
+				t.Errorf("[spec %d] expected console bg attribute at (%d, %d) to be %d; got %d", specIndex, spec.x, spec.y, term.curBg, cons.bgAttrs[offset])
+			}
+		}
+	})
+}
+
+func TestVtLineFeedHandling(t *testing.T) {
+	t.Run("viewport at end of terminal", func(t *testing.T) {
+		cons := newMockConsole(80, 25)
+
+		term := NewVT(4, 0)
+		term.SetState(StateActive)
+		term.AttachTo(cons)
+
+		// Fill last line except the last column which will trigger a
+		// line feed. Cursor position will be automatically clipped to
+		// the viewport bounds
+		term.SetCursorPosition(1, term.viewportHeight+1)
+		for i := uint16(0); i < term.viewportWidth-1; i++ {
+			term.WriteByte(byte('0' + (i % 10)))
+		}
+
+		// Emulate viewportHeight line feeds. The last one should cause a scroll
+		term.SetCursorPosition(0, 0) // cursor is set to (1,1)
+		for i := uint16(0); i < term.viewportHeight; i++ {
+			term.lf(true)
+		}
+
+		if cons.scrollUpCount != 1 {
+			t.Fatalf("expected console to be scrolled up 1 time; got %d", cons.scrollUpCount)
+		}
+
+		// Set cursor one line above the last; this line should now
+		// contain the scrolled contents
+		term.SetCursorPosition(1, term.viewportHeight-1)
+		for col, offset := uint16(1), term.dataOffset; col <= term.viewportWidth; col, offset = col+1, offset+3 {
+			expByte := byte('0' + ((col - 1) % 10))
+			if col == term.viewportWidth {
+				expByte = ' '
+			}
+
+			if term.data[offset] != expByte {
+				t.Errorf("expected char at (%d, %d) to be %q; got %q", col, term.viewportHeight-1, expByte, term.data[offset])
+			}
+		}
+
+		// Set cursor to the last line. This line should now be cleared
+		term.SetCursorPosition(1, term.viewportHeight)
+		for col, offset := uint16(1), term.dataOffset; col <= term.viewportWidth; col, offset = col+1, offset+3 {
+			expByte := uint8(' ')
+			if term.data[offset] != expByte {
+				t.Errorf("expected char at (%d, %d) to be %q; got %q", col, term.viewportHeight, expByte, term.data[offset])
+			}
+		}
+	})
+
+	t.Run("viewport not at end of terminal", func(t *testing.T) {
+		cons := newMockConsole(80, 25)
+
+		term := NewVT(4, 1)
+		term.SetState(StateActive)
+		term.AttachTo(cons)
+
+		// Fill last line except the last column which will trigger a
+		// line feed. Cursor position will be automatically clipped to
+		// the viewport bounds
+		term.SetCursorPosition(1, term.viewportHeight+1)
+		for i := uint16(0); i < term.viewportWidth-1; i++ {
+			term.WriteByte(byte('0' + (i % 10)))
+		}
+
+		// Fill first line including the last column
+		term.SetCursorPosition(1, 1)
+		for i := uint16(0); i < term.viewportWidth; i++ {
+			term.WriteByte(byte('0' + (i % 10)))
+		}
+
+		// Emulate viewportHeight line feeds. The last one should cause a scroll
+		// in the console but only a viewport adjustment in the terminal
+		term.SetCursorPosition(0, 0) // cursor is set to (1,1)
+		for i := uint16(0); i < term.viewportHeight; i++ {
+			term.lf(true)
+		}
+
+		if cons.scrollUpCount != 1 {
+			t.Fatalf("expected console to be scrolled up 1 time; got %d", cons.scrollUpCount)
+		}
+
+		if expViewportY := uint16(1); term.viewportY != expViewportY {
+			t.Fatalf("expected terminal viewportY to be adjusted to %d; got %d", expViewportY, term.viewportY)
+		}
+
+		// Check that first line is still available in the terminal buffer
+		// that is not currently visible
+		term.SetCursorPosition(1, 1)
+		offset := term.dataOffset - uint(term.viewportWidth*3)
+
+		for col := uint16(1); col <= term.viewportWidth; col, offset = col+1, offset+3 {
+			expByte := byte('0' + ((col - 1) % 10))
+
+			if term.data[offset] != expByte {
+				t.Errorf("expected char at hidden region (%d, -1) to be %q; got %q", col, expByte, term.data[offset])
+			}
+		}
+	})
+}
+
+func TestVtAttach(t *testing.T) {
+	cons := newMockConsole(80, 25)
+
+	term := NewVT(4, 1)
+
+	// AttachTo with a nil console should be a no-op
+	term.AttachTo(nil)
+	if term.termWidth != 0 || term.termHeight != 0 || term.viewportWidth != 0 || term.viewportHeight != 0 {
+		t.Fatal("expected attaching a nil console to be a no-op")
+	}
+
+	term.AttachTo(cons)
+	if term.termWidth != cons.width ||
+		term.termHeight != cons.height+term.scrollback ||
+		term.viewportWidth != cons.width ||
+		term.viewportHeight != cons.height ||
+		term.data == nil {
+		t.Fatal("expected the terminal to initialize using the attached console info")
+	}
+}
+
+func TestVtSetState(t *testing.T) {
+	cons := newMockConsole(80, 25)
+	term := NewVT(4, 1)
+	term.AttachTo(cons)
+
+	// Fill terminal viewport using a rotating pattern. Writing the last
+	// character will cause a scroll operation moving the viewport down
+	row := 0
+	for index := 0; index < int(term.viewportWidth*term.viewportHeight); index++ {
+		if index != 0 && index%int(term.viewportWidth) == 0 {
+			row++
+		}
+		term.curFg = uint8((row + index + 1) % 10)
+		term.curBg = uint8((row + index + 2) % 10)
+		term.WriteByte(byte('0' + (row+index)%10))
+	}
+
+	// Activating this terminal should trigger a copy of the terminal viewport
+	// contents to the console.
+	term.SetState(StateActive)
+	row = 1
+	for index := 0; index < len(cons.chars); index++ {
+		if index != 0 && index%int(cons.width) == 0 {
+			row++
+		}
+
+		expCh := uint8('0' + (row+index)%10)
+		expFg := uint8((row + index + 1) % 10)
+		expBg := uint8((row + index + 2) % 10)
+
+		// last line should be cleared due to the scroll operation
+		if row == int(cons.height) {
+			expCh = ' '
+			expFg = 7
+			expBg = 0
+		}
+
+		if cons.chars[index] != expCh {
+			t.Errorf("expected console char at index %d to be %q; got %q", index, expCh, cons.chars[index])
+		}
+
+		if cons.fgAttrs[index] != expFg {
+			t.Errorf("expected console fg attr at index %d to be %d; got %d", index, expFg, cons.fgAttrs[index])
+		}
+
+		if cons.bgAttrs[index] != expBg {
+			t.Errorf("expected console bg attr at index %d to be %d; got %d", index, expBg, cons.bgAttrs[index])
+		}
+	}
+}
+
+func TestVTDriverInterface(t *testing.T) {
+	var dev device.Driver = NewVT(0, 0)
+
+	if err := dev.DriverInit(); err != nil {
+		t.Fatal(err)
+	}
+
+	if dev.DriverName() == "" {
+		t.Fatal("DriverName() returned an empty string")
+	}
+
+	if major, minor, patch := dev.DriverVersion(); major+minor+patch == 0 {
+		t.Fatal("DriverVersion() returned an invalid version number")
+	}
+}
+
+func TestVTProbe(t *testing.T) {
+	var (
+		expProbePtr = reflect.ValueOf(probeForVT).Pointer()
+		foundProbe  bool
+	)
+
+	for _, probeFn := range HWProbes() {
+		if reflect.ValueOf(probeFn).Pointer() == expProbePtr {
+			foundProbe = true
+			break
+		}
+	}
+
+	if !foundProbe {
+		t.Fatal("expected probeForVT to be part of the probes returned by HWProbes")
+	}
+
+	if drv := probeForVT(); drv == nil {
+		t.Fatal("expected probeForVT to return a driver")
+	}
+}
+
+type mockConsole struct {
+	width, height   uint16
+	fg, bg          uint8
+	chars           []uint8
+	fgAttrs         []uint8
+	bgAttrs         []uint8
+	bytesWritten    int
+	scrollUpCount   int
+	scrollDownCount int
+}
+
+func newMockConsole(w, h uint16) *mockConsole {
+	return &mockConsole{
+		width:   w,
+		height:  h,
+		fg:      7,
+		bg:      0,
+		chars:   make([]uint8, w*h),
+		fgAttrs: make([]uint8, w*h),
+		bgAttrs: make([]uint8, w*h),
+	}
+}
+
+func (cons *mockConsole) Dimensions() (uint16, uint16) {
+	return cons.width, cons.height
+}
+
+func (cons *mockConsole) DefaultColors() (uint8, uint8) {
+	return cons.fg, cons.bg
+}
+
+func (cons *mockConsole) Fill(x, y, width, height uint16, fg, bg uint8) {
+	yEnd := y + height - 1
+	xEnd := x + width - 1
+
+	for fy := y; fy <= yEnd; fy++ {
+		offset := ((fy - 1) * cons.width)
+		for fx := x; fx <= xEnd; fx, offset = fx+1, offset+1 {
+			cons.chars[offset] = ' '
+			cons.fgAttrs[offset] = fg
+			cons.bgAttrs[offset] = bg
+		}
+	}
+}
+
+func (cons *mockConsole) Scroll(dir console.ScrollDir, lines uint16) {
+	switch dir {
+	case console.ScrollDirUp:
+		cons.scrollUpCount++
+	case console.ScrollDirDown:
+		cons.scrollDownCount++
+	}
+}
+
+func (cons *mockConsole) Palette() color.Palette {
+	return nil
+}
+
+func (cons *mockConsole) SetPaletteColor(index uint8, color color.RGBA) {
+}
+
+func (cons *mockConsole) Write(b byte, fg, bg uint8, x, y uint16) {
+	offset := ((y - 1) * cons.width) + (x - 1)
+	cons.chars[offset] = b
+	cons.fgAttrs[offset] = fg
+	cons.bgAttrs[offset] = bg
+	cons.bytesWritten++
+}

src/gopheros/device/video/console/device.go

@@ -0,0 +1,45 @@
+package console
+
+import "image/color"
+
+// ScrollDir defines a scroll direction.
+type ScrollDir uint8
+
+// The supported list of scroll directions for the console Scroll() calls.
+const (
+	ScrollDirUp ScrollDir = iota
+	ScrollDirDown
+)
+
+// The Device interface is implemented by objects that can function as system
+// consoles.
+type Device interface {
+	// Dimensions returns the width and height of the console in characters.
+	Dimensions() (uint16, uint16)
+
+	// DefaultColors returns the default foreground and background colors
+	// used by this console.
+	DefaultColors() (fg, bg uint8)
+
+	// Fill sets the contents of the specified rectangular region to the
+	// requested color. Both x and y coordinates are 1-based (top-left
+	// corner has coordinates 1,1).
+	Fill(x, y, width, height uint16, fg, bg uint8)
+
+	// Scroll the console contents to the specified direction. The caller
+	// is responsible for updating (e.g. clear or replace) the contents of
+	// the region that was scrolled.
+	Scroll(dir ScrollDir, lines uint16)
+
+	// Write a char to the specified location. Both x and y coordinates are
+	// 1-based (top-left corner has coordinates 1,1).
+	Write(ch byte, fg, bg uint8, x, y uint16)
+
+	// Palette returns the active color palette for this console.
+	Palette() color.Palette
+
+	// SetPaletteColor updates the color definition for the specified
+	// palette index. Passing a color index greated than the number of
+	// supported colors should be a no-op.
+	SetPaletteColor(uint8, color.RGBA)
+}

src/gopheros/device/video/console/probe.go

@@ -0,0 +1,16 @@
+package console
+
+import "gopheros/device"
+import "gopheros/kernel/hal/multiboot"
+
+var (
+	getFramebufferInfoFn = multiboot.GetFramebufferInfo
+)
+
+// HWProbes returns a slice of device.ProbeFn that can be used by the hal
+// package to probe for console device hardware.
+func HWProbes() []device.ProbeFn {
+	return []device.ProbeFn{
+		probeForVgaTextConsole,
+	}
+}

src/gopheros/device/video/console/vga_text.go

@@ -0,0 +1,212 @@
+package console
+
+import (
+	"gopheros/device"
+	"gopheros/kernel"
+	"gopheros/kernel/cpu"
+	"gopheros/kernel/hal/multiboot"
+	"image/color"
+	"reflect"
+	"unsafe"
+)
+
+var portWriteByteFn = cpu.PortWriteByte
+
+// VgaTextConsole implements an EGA-compatible 80x25 text console using VGA
+// mode 0x3. The console supports the default 16 EGA colors which can be
+// overridden using the SetPaletteColor method.
+//
+// Each character in the console framebuffer is represented using two bytes,
+// a byte for the character ASCII code and a byte that encodes the foreground
+// and background colors (4 bits for each).
+//
+// The default settings for the console are:
+//  - light gray text (color 7) on black background (color 0).
+//  - space as the clear character
+type VgaTextConsole struct {
+	width  uint16
+	height uint16
+
+	fb []uint16
+
+	palette   color.Palette
+	defaultFg uint8
+	defaultBg uint8
+	clearChar uint16
+}
+
+// NewVgaTextConsole creates an new vga text console with its
+// framebuffer mapped to fbPhysAddr.
+func NewVgaTextConsole(columns, rows uint16, fbPhysAddr uintptr) *VgaTextConsole {
+	return &VgaTextConsole{
+		width:     columns,
+		height:    rows,
+		clearChar: uint16(' '),
+		// overlay a 16bit slice over the fbPhysAddr
+		fb: *(*[]uint16)(unsafe.Pointer(&reflect.SliceHeader{
+			Len:  80 * 25,
+			Cap:  80 * 25,
+			Data: fbPhysAddr,
+		})),
+		palette: color.Palette{
+			color.RGBA{R: 0, G: 0, B: 1},       /* black */
+			color.RGBA{R: 0, G: 0, B: 128},     /* blue */
+			color.RGBA{R: 0, G: 128, B: 1},     /* green */
+			color.RGBA{R: 0, G: 128, B: 128},   /* cyan */
+			color.RGBA{R: 128, G: 0, B: 1},     /* red */
+			color.RGBA{R: 128, G: 0, B: 128},   /* magenta */
+			color.RGBA{R: 64, G: 64, B: 1},     /* brown */
+			color.RGBA{R: 128, G: 128, B: 128}, /* light gray */
+			color.RGBA{R: 64, G: 64, B: 64},    /* dark gray */
+			color.RGBA{R: 0, G: 0, B: 255},     /* light blue */
+			color.RGBA{R: 0, G: 255, B: 1},     /* light green */
+			color.RGBA{R: 0, G: 255, B: 255},   /* light cyan */
+			color.RGBA{R: 255, G: 0, B: 1},     /* light red */
+			color.RGBA{R: 255, G: 0, B: 255},   /* light magenta */
+			color.RGBA{R: 255, G: 255, B: 1},   /* yellow */
+			color.RGBA{R: 255, G: 255, B: 255}, /* white */
+		},
+		// light gray text on black background
+		defaultFg: 7,
+		defaultBg: 0,
+	}
+}
+
+// Dimensions returns the console width and height in characters.
+func (cons *VgaTextConsole) Dimensions() (uint16, uint16) {
+	return cons.width, cons.height
+}
+
+// DefaultColors returns the default foreground and background colors
+// used by this console.
+func (cons *VgaTextConsole) DefaultColors() (fg uint8, bg uint8) {
+	return cons.defaultFg, cons.defaultBg
+}
+
+// Fill sets the contents of the specified rectangular region to the requested
+// color. Both x and y coordinates are 1-based.
+func (cons *VgaTextConsole) Fill(x, y, width, height uint16, fg, bg uint8) {
+	var (
+		clr                  = (((uint16(bg) << 4) | uint16(fg)) << 8) | cons.clearChar
+		rowOffset, colOffset uint16
+	)
+
+	// clip rectangle
+	if x == 0 {
+		x = 1
+	} else if x >= cons.width {
+		x = cons.width
+	}
+
+	if y == 0 {
+		y = 1
+	} else if y >= cons.height {
+		y = cons.height
+	}
+
+	if x+width > cons.width {
+		width = cons.width - x
+	}
+
+	if y+height > cons.height {
+		height = cons.height - y
+	}
+
+	rowOffset = ((y - 1) * cons.width) + (x - 1)
+	for ; height > 0; height, rowOffset = height-1, rowOffset+cons.width {
+		for colOffset = rowOffset; colOffset < rowOffset+width; colOffset++ {
+			cons.fb[colOffset] = clr
+		}
+	}
+}
+
+// Scroll the console contents to the specified direction. The caller
+// is responsible for updating (e.g. clear or replace) the contents of
+// the region that was scrolled.
+func (cons *VgaTextConsole) Scroll(dir ScrollDir, lines uint16) {
+	if lines == 0 || lines > cons.height {
+		return
+	}
+
+	var i uint16
+	offset := lines * cons.width
+
+	switch dir {
+	case ScrollDirUp:
+		for ; i < (cons.height-lines)*cons.width; i++ {
+			cons.fb[i] = cons.fb[i+offset]
+		}
+	case ScrollDirDown:
+		for i = cons.height*cons.width - 1; i >= lines*cons.width; i-- {
+			cons.fb[i] = cons.fb[i-offset]
+		}
+	}
+}
+
+// Write a char to the specified location. If fg or bg exceed the supported
+// colors for this console, they will be set to their default value. Both x and
+// y coordinates are 1-based
+func (cons *VgaTextConsole) Write(ch byte, fg, bg uint8, x, y uint16) {
+	if x < 1 || x > cons.width || y < 1 || y > cons.height {
+		return
+	}
+
+	maxColorIndex := uint8(len(cons.palette) - 1)
+	if fg > maxColorIndex {
+		fg = cons.defaultFg
+	}
+	if bg >= maxColorIndex {
+		bg = cons.defaultBg
+	}
+
+	cons.fb[((y-1)*cons.width)+(x-1)] = (((uint16(bg) << 4) | uint16(fg)) << 8) | uint16(ch)
+}
+
+// Palette returns the active color palette for this console.
+func (cons *VgaTextConsole) Palette() color.Palette {
+	return cons.palette
+}
+
+// SetPaletteColor updates the color definition for the specified
+// palette index. Passing a color index greated than the number of
+// supported colors should be a no-op.
+func (cons *VgaTextConsole) SetPaletteColor(index uint8, rgba color.RGBA) {
+	if index >= uint8(len(cons.palette)) {
+		return
+	}
+
+	cons.palette[index] = rgba
+
+	// Load palette entry to the DAC. In this mode, colors are specified
+	// using 6-bits for each component; the RGB values need to be converted
+	// to the 0-63 range.
+	portWriteByteFn(0x3c8, index)
+	portWriteByteFn(0x3c9, rgba.R>>2)
+	portWriteByteFn(0x3c9, rgba.G>>2)
+	portWriteByteFn(0x3c9, rgba.B>>2)
+}
+
+// DriverName returns the name of this driver.
+func (cons *VgaTextConsole) DriverName() string {
+	return "vga_text_console"
+}
+
+// DriverVersion returns the version of this driver.
+func (cons *VgaTextConsole) DriverVersion() (uint16, uint16, uint16) {
+	return 0, 0, 1
+}
+
+// DriverInit initializes this driver.
+func (cons *VgaTextConsole) DriverInit() *kernel.Error { return nil }
+
+// probeForVgaTextConsole checks for the presence of a vga text console.
+func probeForVgaTextConsole() device.Driver {
+	var drv device.Driver
+
+	fbInfo := getFramebufferInfoFn()
+	if fbInfo.Type == multiboot.FramebufferTypeEGA {
+		drv = NewVgaTextConsole(uint16(fbInfo.Width), uint16(fbInfo.Height), uintptr(fbInfo.PhysAddr))
+	}
+
+	return drv
+}

src/gopheros/device/video/console/vga_text_test.go

@@ -0,0 +1,358 @@
+package console
+
+import (
+	"gopheros/device"
+	"gopheros/kernel/cpu"
+	"gopheros/kernel/hal/multiboot"
+	"image/color"
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+func TestVgaTextDimensions(t *testing.T) {
+	cons := NewVgaTextConsole(80, 25, 0)
+	if w, h := cons.Dimensions(); w != 80 || h != 25 {
+		t.Fatalf("expected console dimensions to be 80x25; got %dx%d", w, h)
+	}
+}
+
+func TestVgaTextDefaultColors(t *testing.T) {
+	cons := NewVgaTextConsole(80, 25, 0)
+	if fg, bg := cons.DefaultColors(); fg != 7 || bg != 0 {
+		t.Fatalf("expected console default colors to be fg:7, bg:0; got fg:%d, bg: %d", fg, bg)
+	}
+}
+
+func TestVgaTextFill(t *testing.T) {
+	specs := []struct {
+		// Input rect
+		x, y, w, h uint16
+
+		// Expected area to be cleared
+		expX, expY, expW, expH uint16
+	}{
+		{
+			0, 0, 500, 500,
+			0, 0, 80, 25,
+		},
+		{
+			10, 10, 11, 50,
+			10, 10, 11, 15,
+		},
+		{
+			10, 10, 110, 1,
+			10, 10, 70, 1,
+		},
+		{
+			70, 20, 20, 20,
+			70, 20, 10, 5,
+		},
+		{
+			90, 25, 20, 20,
+			0, 0, 0, 0,
+		},
+		{
+			12, 12, 5, 6,
+			12, 12, 5, 6,
+		},
+	}
+
+	fb := make([]uint16, 80*25)
+	cons := NewVgaTextConsole(80, 25, uintptr(unsafe.Pointer(&fb[0])))
+	cw, ch := cons.Dimensions()
+
+	testPat := uint16(0xDEAD)
+	clearPat := uint16(cons.clearChar)
+
+nextSpec:
+	for specIndex, spec := range specs {
+		// Fill FB with test pattern
+		for i := 0; i < len(fb); i++ {
+			fb[i] = testPat
+		}
+
+		cons.Fill(spec.x, spec.y, spec.w, spec.h, 0, 0)
+
+		var x, y uint16
+		for y = 1; y <= ch; y++ {
+			for x = 1; x <= cw; x++ {
+				fbVal := fb[((y-1)*cw)+(x-1)]
+
+				if x < spec.expX || y < spec.expY || x >= spec.expX+spec.expW || y >= spec.expY+spec.expH {
+					if fbVal != testPat {
+						t.Errorf("[spec %d] expected char at (%d, %d) not to be cleared", specIndex, x, y)
+						continue nextSpec
+					}
+				} else {
+					if fbVal != clearPat {
+						t.Errorf("[spec %d] expected char at (%d, %d) to be cleared", specIndex, x, y)
+						continue nextSpec
+					}
+				}
+			}
+		}
+	}
+}
+
+func TestVgaTextScroll(t *testing.T) {
+	fb := make([]uint16, 80*25)
+	cons := NewVgaTextConsole(80, 25, uintptr(unsafe.Pointer(&fb[0])))
+	cw, ch := cons.Dimensions()
+
+	t.Run("up", func(t *testing.T) {
+		specs := []uint16{
+			0,
+			1,
+			2,
+		}
+	nextSpec:
+		for specIndex, lines := range specs {
+			// Fill buffer with test pattern
+			var x, y, index uint16
+			for y = 0; y < ch; y++ {
+				for x = 0; x < cw; x++ {
+					fb[index] = (y << 8) | x
+					index++
+				}
+			}
+
+			cons.Scroll(ScrollDirUp, lines)
+
+			// Check that rows 1 to (height - lines) have been scrolled up
+			index = 0
+			for y = 0; y < ch-lines; y++ {
+				for x = 0; x < cw; x++ {
+					expVal := ((y + lines) << 8) | x
+					if fb[index] != expVal {
+						t.Errorf("[spec %d] expected value at (%d, %d) to be %d; got %d", specIndex, x, y, expVal, fb[index])
+						continue nextSpec
+					}
+					index++
+				}
+			}
+		}
+	})
+
+	t.Run("down", func(t *testing.T) {
+		specs := []uint16{
+			0,
+			1,
+			2,
+		}
+
+	nextSpec:
+		for specIndex, lines := range specs {
+			// Fill buffer with test pattern
+			var x, y, index uint16
+			for y = 0; y < ch; y++ {
+				for x = 0; x < cw; x++ {
+					fb[index] = (y << 8) | x
+					index++
+				}
+			}
+
+			cons.Scroll(ScrollDirDown, lines)
+
+			// Check that rows lines to height have been scrolled down
+			index = lines * cw
+			for y = lines; y < ch-lines; y++ {
+				for x = 0; x < cw; x++ {
+					expVal := ((y - lines) << 8) | x
+					if fb[index] != expVal {
+						t.Errorf("[spec %d] expected value at (%d, %d) to be %d; got %d", specIndex, x, y, expVal, fb[index])
+						continue nextSpec
+					}
+					index++
+				}
+			}
+		}
+	})
+}
+
+func TestVgaTextWrite(t *testing.T) {
+	fb := make([]uint16, 80*25)
+	cons := NewVgaTextConsole(80, 25, uintptr(unsafe.Pointer(&fb[0])))
+	defaultFg, defaultBg := cons.DefaultColors()
+
+	t.Run("off-screen", func(t *testing.T) {
+		specs := []struct {
+			x, y uint16
+		}{
+			{81, 26},
+			{90, 24},
+			{79, 30},
+			{100, 100},
+		}
+
+	nextSpec:
+		for specIndex, spec := range specs {
+			for i := 0; i < len(fb); i++ {
+				fb[i] = 0
+			}
+
+			cons.Write('!', 1, 2, spec.x, spec.y)
+
+			for i := 0; i < len(fb); i++ {
+				if got := fb[i]; got != 0 {
+					t.Errorf("[spec %d] expected Write() with off-screen coords to be a no-op", specIndex)
+					continue nextSpec
+				}
+			}
+		}
+	})
+
+	t.Run("success", func(t *testing.T) {
+		for i := 0; i < len(fb); i++ {
+			fb[i] = 0
+		}
+
+		fg := uint8(1)
+		bg := uint8(2)
+		expAttr := uint16((uint16(bg) << 4) | uint16(fg))
+
+		cons.Write('!', fg, bg, 1, 1)
+
+		expVal := (expAttr << 8) | uint16('!')
+		if got := fb[0]; got != expVal {
+			t.Errorf("expected call to Write() to set fb[0] to %d; got %d", expVal, got)
+		}
+	})
+
+	t.Run("fg out of range", func(t *testing.T) {
+		for i := 0; i < len(fb); i++ {
+			fb[i] = 0
+		}
+
+		fg := uint8(128)
+		bg := uint8(2)
+		expAttr := uint16((uint16(bg) << 4) | uint16(defaultFg))
+
+		cons.Write('!', fg, bg, 1, 1)
+
+		expVal := (expAttr << 8) | uint16('!')
+		if got := fb[0]; got != expVal {
+			t.Errorf("expected call to Write() to set fb[0] to %d; got %d", expVal, got)
+		}
+	})
+
+	t.Run("bg out of range", func(t *testing.T) {
+		for i := 0; i < len(fb); i++ {
+			fb[i] = 0
+		}
+
+		fg := uint8(8)
+		bg := uint8(255)
+		expAttr := uint16((uint16(defaultBg) << 4) | uint16(fg))
+
+		cons.Write('!', fg, bg, 1, 1)
+
+		expVal := (expAttr << 8) | uint16('!')
+		if got := fb[0]; got != expVal {
+			t.Errorf("expected call to Write() to set fb[0] to %d; got %d", expVal, got)
+		}
+	})
+}
+
+func TestVgaTextSetPaletteColor(t *testing.T) {
+	defer func() {
+		portWriteByteFn = cpu.PortWriteByte
+	}()
+
+	cons := NewVgaTextConsole(80, 25, 0)
+
+	t.Run("success", func(t *testing.T) {
+		expWrites := []struct {
+			port uint16
+			val  uint8
+		}{
+			// Values will be normalized in the 0-31 range
+			{0x3c8, 1},
+			{0x3c9, 63},
+			{0x3c9, 31},
+			{0x3c9, 0},
+		}
+
+		writeCallCount := 0
+		portWriteByteFn = func(port uint16, val uint8) {
+			exp := expWrites[writeCallCount]
+			if port != exp.port || val != exp.val {
+				t.Errorf("[port write %d] expected port: 0x%x, val: %d; got port: 0x%x, val: %d", writeCallCount, exp.port, exp.val, port, val)
+			}
+
+			writeCallCount++
+		}
+
+		rgba := color.RGBA{R: 255, G: 127, B: 0}
+		cons.SetPaletteColor(1, rgba)
+
+		if got := cons.Palette()[1]; got != rgba {
+			t.Errorf("expected color at index 1 to be:\n%v\ngot:\n%v", rgba, got)
+		}
+
+		if writeCallCount != len(expWrites) {
+			t.Errorf("expected cpu.portWriteByty to be called %d times; got %d", len(expWrites), writeCallCount)
+		}
+	})
+
+	t.Run("color index out of range", func(t *testing.T) {
+		portWriteByteFn = func(_ uint16, _ uint8) {
+			t.Error("unexpected call to cpu.PortWriteByte")
+		}
+
+		rgba := color.RGBA{R: 255, G: 127, B: 0}
+		cons.SetPaletteColor(50, rgba)
+	})
+}
+
+func TestVgaTextDriverInterface(t *testing.T) {
+	var dev device.Driver = NewVgaTextConsole(80, 25, 0)
+
+	if err := dev.DriverInit(); err != nil {
+		t.Fatal(err)
+	}
+
+	if dev.DriverName() == "" {
+		t.Fatal("DriverName() returned an empty string")
+	}
+
+	if major, minor, patch := dev.DriverVersion(); major+minor+patch == 0 {
+		t.Fatal("DriverVersion() returned an invalid version number")
+	}
+}
+
+func TestVgaTextProbe(t *testing.T) {
+	defer func() {
+		getFramebufferInfoFn = multiboot.GetFramebufferInfo
+	}()
+
+	var (
+		expProbePtr = reflect.ValueOf(probeForVgaTextConsole).Pointer()
+		foundProbe  bool
+	)
+
+	for _, probeFn := range HWProbes() {
+		if reflect.ValueOf(probeFn).Pointer() == expProbePtr {
+			foundProbe = true
+			break
+		}
+	}
+
+	if !foundProbe {
+		t.Fatal("expected probeForVgaTextConsole to be part of the probes returned by HWProbes")
+	}
+
+	getFramebufferInfoFn = func() *multiboot.FramebufferInfo {
+		return &multiboot.FramebufferInfo{
+			Width:    80,
+			Height:   25,
+			Pitch:    160,
+			PhysAddr: 0xb80000,
+			Type:     multiboot.FramebufferTypeEGA,
+		}
+	}
+
+	if drv := probeForVgaTextConsole(); drv == nil {
+		t.Fatal("expected probeForVgaTextConsole to return a driver")
+	}
+}

src/gopheros/kernel/driver/tty/tty.go

@@ -1,19 +0,0 @@
-package tty
-
-import "io"
-
-// Tty is implemented by objects that can register themselves as ttys.
-type Tty interface {
-	io.Writer
-	io.ByteWriter
-
-	// Position returns the current cursor position (x, y).
-	Position() (uint16, uint16)
-
-	// SetPosition sets the current cursor position to (x,y). Console implementations
-	// must clip the provided cursor position if it exceeds the console dimensions.
-	SetPosition(x, y uint16)
-
-	// Clear clears the terminal.
-	Clear()
-}

src/gopheros/kernel/driver/tty/vt.go

@@ -1,128 +0,0 @@
-package tty
-
-import "gopheros/kernel/driver/video/console"
-
-const (
-	defaultFg = console.LightGrey
-	defaultBg = console.Black
-	tabWidth  = 4
-)
-
-// Vt implements a simple terminal that can process LF and CR characters. The
-// terminal uses a console device for its output.
-type Vt struct {
-	// Go interfaces will not work before we can get memory allocation working.
-	// Till then we need to use concrete types instead.
-	cons *console.Ega
-
-	width  uint16
-	height uint16
-
-	curX    uint16
-	curY    uint16
-	curAttr console.Attr
-}
-
-// AttachTo links the terminal with the specified console device and updates
-// the terminal's dimensions to match the ones reported by the attached device.
-func (t *Vt) AttachTo(cons *console.Ega) {
-	t.cons = cons
-	t.width, t.height = cons.Dimensions()
-	t.curX = 0
-	t.curY = 0
-
-	// Default to lightgrey on black text.
-	t.curAttr = makeAttr(defaultFg, defaultBg)
-}
-
-// Clear clears the terminal.
-func (t *Vt) Clear() {
-	t.clear()
-}
-
-// Position returns the current cursor position (x, y).
-func (t *Vt) Position() (uint16, uint16) {
-	return t.curX, t.curY
-}
-
-// SetPosition sets the current cursor position to (x,y).
-func (t *Vt) SetPosition(x, y uint16) {
-	if x >= t.width {
-		x = t.width - 1
-	}
-
-	if y >= t.height {
-		y = t.height - 1
-	}
-
-	t.curX, t.curY = x, y
-}
-
-// Write implements io.Writer.
-func (t *Vt) Write(data []byte) (int, error) {
-	for _, b := range data {
-		t.WriteByte(b)
-	}
-
-	return len(data), nil
-}
-
-// WriteByte implements io.ByteWriter.
-func (t *Vt) WriteByte(b byte) error {
-	switch b {
-	case '\r':
-		t.cr()
-	case '\n':
-		t.cr()
-		t.lf()
-	case '\b':
-		if t.curX > 0 {
-			t.cons.Write(' ', t.curAttr, t.curX, t.curY)
-			t.curX--
-		}
-	case '\t':
-		for i := 0; i < tabWidth; i++ {
-			t.cons.Write(' ', t.curAttr, t.curX, t.curY)
-			t.curX++
-			if t.curX == t.width {
-				t.cr()
-				t.lf()
-			}
-		}
-	default:
-		t.cons.Write(b, t.curAttr, t.curX, t.curY)
-		t.curX++
-		if t.curX == t.width {
-			t.cr()
-			t.lf()
-		}
-	}
-
-	return nil
-}
-
-// cls clears the terminal.
-func (t *Vt) clear() {
-	t.cons.Clear(0, 0, t.width, t.height)
-}
-
-// cr resets the x coordinate of the terminal cursor to 0.
-func (t *Vt) cr() {
-	t.curX = 0
-}
-
-// lf advances the y coordinate of the terminal cursor by one line scrolling
-// the terminal contents if the end of the last terminal line is reached.
-func (t *Vt) lf() {
-	if t.curY+1 < t.height {
-		t.curY++
-		return
-	}
-
-	t.cons.Scroll(console.Up, 1)
-	t.cons.Clear(0, t.height-1, t.width, 1)
-}
-
-func makeAttr(fg, bg console.Attr) console.Attr {
-	return (bg << 4) | (fg & 0xF)
-}

src/gopheros/kernel/driver/tty/vt_test.go

@@ -1,88 +0,0 @@
-package tty
-
-import (
-	"gopheros/kernel/driver/video/console"
-	"testing"
-	"unsafe"
-)
-
-func TestVtPosition(t *testing.T) {
-	specs := []struct {
-		inX, inY   uint16
-		expX, expY uint16
-	}{
-		{20, 20, 20, 20},
-		{100, 20, 79, 20},
-		{10, 200, 10, 24},
-		{10, 200, 10, 24},
-		{100, 100, 79, 24},
-	}
-
-	fb := make([]uint16, 80*25)
-	var cons console.Ega
-	cons.Init(80, 25, uintptr(unsafe.Pointer(&fb[0])))
-
-	var vt Vt
-	vt.AttachTo(&cons)
-
-	for specIndex, spec := range specs {
-		vt.SetPosition(spec.inX, spec.inY)
-		if x, y := vt.Position(); x != spec.expX || y != spec.expY {
-			t.Errorf("[spec %d] expected setting position to (%d, %d) to update the position to (%d, %d); got (%d, %d)", specIndex, spec.inX, spec.inY, spec.expX, spec.expY, x, y)
-		}
-	}
-}
-
-func TestWrite(t *testing.T) {
-	fb := make([]uint16, 80*25)
-	var cons console.Ega
-	cons.Init(80, 25, uintptr(unsafe.Pointer(&fb[0])))
-
-	var vt Vt
-	vt.AttachTo(&cons)
-
-	vt.Clear()
-	vt.SetPosition(0, 1)
-	vt.Write([]byte("12\n\t3\n4\r567\b8"))
-
-	// Tab spanning rows
-	vt.SetPosition(78, 4)
-	vt.WriteByte('\t')
-	vt.WriteByte('9')
-
-	// Trigger scroll
-	vt.SetPosition(79, 24)
-	vt.Write([]byte{'!'})
-
-	specs := []struct {
-		x, y    uint16
-		expChar byte
-	}{
-		{0, 0, '1'},
-		{1, 0, '2'},
-		// tabs
-		{0, 1, ' '},
-		{1, 1, ' '},
-		{2, 1, ' '},
-		{3, 1, ' '},
-		{4, 1, '3'},
-		// tab spanning 2 rows
-		{78, 3, ' '},
-		{79, 3, ' '},
-		{0, 4, ' '},
-		{1, 4, ' '},
-		{2, 4, '9'},
-		//
-		{0, 2, '5'},
-		{1, 2, '6'},
-		{2, 2, '8'}, // overwritten by BS
-		{79, 23, '!'},
-	}
-
-	for specIndex, spec := range specs {
-		ch := (byte)(fb[(spec.y*vt.width)+spec.x] & 0xFF)
-		if ch != spec.expChar {
-			t.Errorf("[spec %d] expected char at (%d, %d) to be %c; got %c", specIndex, spec.x, spec.y, spec.expChar, ch)
-		}
-	}
-}

src/gopheros/kernel/driver/video/console/console.go

@@ -1,48 +0,0 @@
-package console
-
-// Attr defines a color attribute.
-type Attr uint16
-
-// The set of attributes that can be passed to Write().
-const (
-	Black Attr = iota
-	Blue
-	Green
-	Cyan
-	Red
-	Magenta
-	Brown
-	LightGrey
-	Grey
-	LightBlue
-	LightGreen
-	LightCyan
-	LightRed
-	LightMagenta
-	LightBrown
-	White
-)
-
-// ScrollDir defines a scroll direction.
-type ScrollDir uint8
-
-// The supported list of scroll directions for the console Scroll() calls.
-const (
-	Up ScrollDir = iota
-	Down
-)
-
-// The Console interface is implemented by objects that can function as physical consoles.
-type Console interface {
-	// Dimensions returns the width and height of the console in characters.
-	Dimensions() (uint16, uint16)
-
-	// Clear clears the specified rectangular region
-	Clear(x, y, width, height uint16)
-
-	// Scroll a particular number of lines to the specified direction.
-	Scroll(dir ScrollDir, lines uint16)
-
-	// Write a char to the specified location.
-	Write(ch byte, attr Attr, x, y uint16)
-}

src/gopheros/kernel/driver/video/console/ega.go

@@ -1,100 +0,0 @@
-package console
-
-import (
-	"reflect"
-	"unsafe"
-)
-
-const (
-	clearColor = Black
-	clearChar  = byte(' ')
-)
-
-// Ega implements an EGA-compatible text console. At the moment, it uses the
-// ega console physical address as its outpucons. After implementing a memory
-// allocator, each console will use its own framebuffer while the active console
-// will periodically sync its internal buffer with the physical screen buffer.
-type Ega struct {
-	width  uint16
-	height uint16
-
-	fb []uint16
-}
-
-// Init sets up the console.
-func (cons *Ega) Init(width, height uint16, fbPhysAddr uintptr) {
-	cons.width = width
-	cons.height = height
-
-	cons.fb = *(*[]uint16)(unsafe.Pointer(&reflect.SliceHeader{
-		Len:  int(cons.width * cons.height),
-		Cap:  int(cons.width * cons.height),
-		Data: fbPhysAddr,
-	}))
-}
-
-// Clear clears the specified rectangular region
-func (cons *Ega) Clear(x, y, width, height uint16) {
-	var (
-		attr                 = uint16((clearColor << 4) | clearColor)
-		clr                  = attr | uint16(clearChar)
-		rowOffset, colOffset uint16
-	)
-
-	// clip rectangle
-	if x >= cons.width {
-		x = cons.width
-	}
-	if y >= cons.height {
-		y = cons.height
-	}
-
-	if x+width > cons.width {
-		width = cons.width - x
-	}
-	if y+height > cons.height {
-		height = cons.height - y
-	}
-
-	rowOffset = (y * cons.width) + x
-	for ; height > 0; height, rowOffset = height-1, rowOffset+cons.width {
-		for colOffset = rowOffset; colOffset < rowOffset+width; colOffset++ {
-			cons.fb[colOffset] = clr
-		}
-	}
-}
-
-// Dimensions returns the console width and height in characters.
-func (cons *Ega) Dimensions() (uint16, uint16) {
-	return cons.width, cons.height
-}
-
-// Scroll a particular number of lines to the specified direction.
-func (cons *Ega) Scroll(dir ScrollDir, lines uint16) {
-	if lines == 0 || lines > cons.height {
-		return
-	}
-
-	var i uint16
-	offset := lines * cons.width
-
-	switch dir {
-	case Up:
-		for ; i < (cons.height-lines)*cons.width; i++ {
-			cons.fb[i] = cons.fb[i+offset]
-		}
-	case Down:
-		for i = cons.height*cons.width - 1; i >= lines*cons.width; i-- {
-			cons.fb[i] = cons.fb[i-offset]
-		}
-	}
-}
-
-// Write a char to the specified location.
-func (cons *Ega) Write(ch byte, attr Attr, x, y uint16) {
-	if x >= cons.width || y >= cons.height {
-		return
-	}
-
-	cons.fb[(y*cons.width)+x] = (uint16(attr) << 8) | uint16(ch)
-}

src/gopheros/kernel/driver/video/console/ega_test.go

@@ -1,212 +0,0 @@
-package console
-
-import (
-	"testing"
-	"unsafe"
-)
-
-func TestEgaInit(t *testing.T) {
-	var cons Ega
-	cons.Init(80, 25, 0xB8000)
-
-	var expWidth uint16 = 80
-	var expHeight uint16 = 25
-
-	if w, h := cons.Dimensions(); w != expWidth || h != expHeight {
-		t.Fatalf("expected console dimensions after Init() to be (%d, %d); got (%d, %d)", expWidth, expHeight, w, h)
-	}
-}
-
-func TestEgaClear(t *testing.T) {
-	specs := []struct {
-		// Input rect
-		x, y, w, h uint16
-
-		// Expected area to be cleared
-		expX, expY, expW, expH uint16
-	}{
-		{
-			0, 0, 500, 500,
-			0, 0, 80, 25,
-		},
-		{
-			10, 10, 11, 50,
-			10, 10, 11, 15,
-		},
-		{
-			10, 10, 110, 1,
-			10, 10, 70, 1,
-		},
-		{
-			70, 20, 20, 20,
-			70, 20, 10, 5,
-		},
-		{
-			90, 25, 20, 20,
-			0, 0, 0, 0,
-		},
-		{
-			12, 12, 5, 6,
-			12, 12, 5, 6,
-		},
-	}
-
-	fb := make([]uint16, 80*25)
-	var cons Ega
-	cons.Init(80, 25, uintptr(unsafe.Pointer(&fb[0])))
-
-	testPat := uint16(0xDEAD)
-	clearPat := (uint16(clearColor) << 8) | uint16(clearChar)
-
-nextSpec:
-	for specIndex, spec := range specs {
-		// Fill FB with test pattern
-		for i := 0; i < len(cons.fb); i++ {
-			fb[i] = testPat
-		}
-
-		cons.Clear(spec.x, spec.y, spec.w, spec.h)
-
-		var x, y uint16
-		for y = 0; y < cons.height; y++ {
-			for x = 0; x < cons.width; x++ {
-				fbVal := fb[(y*cons.width)+x]
-
-				if x < spec.expX || y < spec.expY || x >= spec.expX+spec.expW || y >= spec.expY+spec.expH {
-					if fbVal != testPat {
-						t.Errorf("[spec %d] expected char at (%d, %d) not to be cleared", specIndex, x, y)
-						continue nextSpec
-					}
-				} else {
-					if fbVal != clearPat {
-						t.Errorf("[spec %d] expected char at (%d, %d) to be cleared", specIndex, x, y)
-						continue nextSpec
-					}
-				}
-			}
-		}
-	}
-}
-
-func TestEgaScrollUp(t *testing.T) {
-	specs := []uint16{
-		0,
-		1,
-		2,
-	}
-
-	fb := make([]uint16, 80*25)
-	var cons Ega
-	cons.Init(80, 25, uintptr(unsafe.Pointer(&fb[0])))
-
-nextSpec:
-	for specIndex, lines := range specs {
-		// Fill buffer with test pattern
-		var x, y, index uint16
-		for y = 0; y < cons.height; y++ {
-			for x = 0; x < cons.width; x++ {
-				fb[index] = (y << 8) | x
-				index++
-			}
-		}
-
-		cons.Scroll(Up, lines)
-
-		// Check that rows 1 to (height - lines) have been scrolled up
-		index = 0
-		for y = 0; y < cons.height-lines; y++ {
-			for x = 0; x < cons.width; x++ {
-				expVal := ((y + lines) << 8) | x
-				if fb[index] != expVal {
-					t.Errorf("[spec %d] expected value at (%d, %d) to be %d; got %d", specIndex, x, y, expVal, cons.fb[index])
-					continue nextSpec
-				}
-				index++
-			}
-		}
-	}
-}
-
-func TestEgaScrollDown(t *testing.T) {
-	specs := []uint16{
-		0,
-		1,
-		2,
-	}
-
-	fb := make([]uint16, 80*25)
-	var cons Ega
-	cons.Init(80, 25, uintptr(unsafe.Pointer(&fb[0])))
-
-nextSpec:
-	for specIndex, lines := range specs {
-		// Fill buffer with test pattern
-		var x, y, index uint16
-		for y = 0; y < cons.height; y++ {
-			for x = 0; x < cons.width; x++ {
-				fb[index] = (y << 8) | x
-				index++
-			}
-		}
-
-		cons.Scroll(Down, lines)
-
-		// Check that rows lines to height have been scrolled down
-		index = lines * cons.width
-		for y = lines; y < cons.height-lines; y++ {
-			for x = 0; x < cons.width; x++ {
-				expVal := ((y - lines) << 8) | x
-				if fb[index] != expVal {
-					t.Errorf("[spec %d] expected value at (%d, %d) to be %d; got %d", specIndex, x, y, expVal, cons.fb[index])
-					continue nextSpec
-				}
-				index++
-			}
-		}
-	}
-}
-
-func TestEgaWriteWithOffScreenCoords(t *testing.T) {
-	fb := make([]uint16, 80*25)
-	var cons Ega
-	cons.Init(80, 25, uintptr(unsafe.Pointer(&fb[0])))
-
-	specs := []struct {
-		x, y uint16
-	}{
-		{80, 25},
-		{90, 24},
-		{79, 30},
-		{100, 100},
-	}
-
-nextSpec:
-	for specIndex, spec := range specs {
-		for i := 0; i < len(cons.fb); i++ {
-			fb[i] = 0
-		}
-
-		cons.Write('!', Red, spec.x, spec.y)
-
-		for i := 0; i < len(cons.fb); i++ {
-			if got := fb[i]; got != 0 {
-				t.Errorf("[spec %d] expected Write() with off-screen coords to be a no-op", specIndex)
-				continue nextSpec
-			}
-		}
-	}
-}
-
-func TestEgaWrite(t *testing.T) {
-	fb := make([]uint16, 80*25)
-	var cons Ega
-	cons.Init(80, 25, uintptr(unsafe.Pointer(&fb[0])))
-
-	attr := (Black << 4) | Red
-	cons.Write('!', attr, 0, 0)
-
-	expVal := uint16(attr<<8) | uint16('!')
-	if got := fb[0]; got != expVal {
-		t.Errorf("expected call to Write() to set fb[0] to %d; got %d", expVal, got)
-	}
-}

src/gopheros/kernel/goruntime/bootstrap_test.go

@@ -266,6 +266,7 @@ func TestInit(t *testing.T) {
 		modulesInitFn = modulesInit
 		typeLinksInitFn = typeLinksInit
 		itabsInitFn = itabsInit
+		initGoPackagesFn = initGoPackages
 	}()
 
 	mallocInitFn = func() {}
@@ -273,6 +274,7 @@ func TestInit(t *testing.T) {
 	modulesInitFn = func() {}
 	typeLinksInitFn = func() {}
 	itabsInitFn = func() {}
+	initGoPackagesFn = func() {}
 
 	if err := Init(); err != nil {
 		t.Fatal(t)

src/gopheros/kernel/hal/hal.go

@@ -1,23 +1,67 @@
 package hal
 
 import (
-	"gopheros/kernel/driver/tty"
-	"gopheros/kernel/driver/video/console"
-	"gopheros/kernel/hal/multiboot"
+	"gopheros/device"
+	"gopheros/device/tty"
+	"gopheros/device/video/console"
+	"gopheros/kernel/kfmt"
 )
 
-var (
-	egaConsole = &console.Ega{}
-
-	// ActiveTerminal points to the currently active terminal.
-	ActiveTerminal = &tty.Vt{}
-)
-
-// InitTerminal provides a basic terminal to allow the kernel to emit some output
-// till everything is properly setup
-func InitTerminal() {
-	fbInfo := multiboot.GetFramebufferInfo()
-
-	egaConsole.Init(uint16(fbInfo.Width), uint16(fbInfo.Height), uintptr(fbInfo.PhysAddr))
-	ActiveTerminal.AttachTo(egaConsole)
+// managedDevices contains the devices discovered by the HAL.
+type managedDevices struct {
+	activeConsole console.Device
+	activeTTY     tty.Device
+}
+
+var devices managedDevices
+
+// ActiveTTY returns the currently active TTY
+func ActiveTTY() tty.Device {
+	return devices.activeTTY
+}
+
+// DetectHardware probes for hardware devices and initializes the appropriate
+// drivers.
+func DetectHardware() {
+	consoles := probe(console.HWProbes())
+	if len(consoles) != 0 {
+		devices.activeConsole = consoles[0].(console.Device)
+	}
+
+	ttys := probe(tty.HWProbes())
+	if len(ttys) != 0 {
+		devices.activeTTY = ttys[0].(tty.Device)
+		devices.activeTTY.AttachTo(devices.activeConsole)
+		kfmt.SetOutputSink(devices.activeTTY)
+
+		// Sync terminal contents with console
+		devices.activeTTY.SetState(tty.StateActive)
+	}
+}
+
+// probe executes the supplied hw probe functions and attempts to initialize
+// each detected device. The function returns a list of device drivers that
+// were successfully initialized.
+func probe(hwProbeFns []device.ProbeFn) []device.Driver {
+	var drivers []device.Driver
+
+	for _, probeFn := range hwProbeFns {
+		drv := probeFn()
+		if drv == nil {
+			continue
+		}
+
+		major, minor, patch := drv.DriverVersion()
+
+		kfmt.Printf("[hal] %s(%d.%d.%d): ", drv.DriverName(), major, minor, patch)
+		if err := drv.DriverInit(); err != nil {
+			kfmt.Printf("init failed: %s\n", err.Message)
+			continue
+		}
+
+		drivers = append(drivers, drv)
+		kfmt.Printf("initialized\n")
+	}
+
+	return drivers
 }

src/gopheros/kernel/irq/interrupt_amd64.go

@@ -1,6 +1,6 @@
 package irq
 
-import "gopheros/kernel/kfmt/early"
+import "gopheros/kernel/kfmt"
 
 // Regs contains a snapshot of the register values when an interrupt occurred.
 type Regs struct {
@@ -23,14 +23,14 @@ type Regs struct {
 
 // Print outputs a dump of the register values to the active console.
 func (r *Regs) Print() {
-	early.Printf("RAX = %16x RBX = %16x\n", r.RAX, r.RBX)
-	early.Printf("RCX = %16x RDX = %16x\n", r.RCX, r.RDX)
-	early.Printf("RSI = %16x RDI = %16x\n", r.RSI, r.RDI)
-	early.Printf("RBP = %16x\n", r.RBP)
-	early.Printf("R8  = %16x R9  = %16x\n", r.R8, r.R9)
-	early.Printf("R10 = %16x R11 = %16x\n", r.R10, r.R11)
-	early.Printf("R12 = %16x R13 = %16x\n", r.R12, r.R13)
-	early.Printf("R14 = %16x R15 = %16x\n", r.R14, r.R15)
+	kfmt.Printf("RAX = %16x RBX = %16x\n", r.RAX, r.RBX)
+	kfmt.Printf("RCX = %16x RDX = %16x\n", r.RCX, r.RDX)
+	kfmt.Printf("RSI = %16x RDI = %16x\n", r.RSI, r.RDI)
+	kfmt.Printf("RBP = %16x\n", r.RBP)
+	kfmt.Printf("R8  = %16x R9  = %16x\n", r.R8, r.R9)
+	kfmt.Printf("R10 = %16x R11 = %16x\n", r.R10, r.R11)
+	kfmt.Printf("R12 = %16x R13 = %16x\n", r.R12, r.R13)
+	kfmt.Printf("R14 = %16x R15 = %16x\n", r.R14, r.R15)
 }
 
 // Frame describes an exception frame that is automatically pushed by the CPU
@@ -45,7 +45,7 @@ type Frame struct {
 
 // Print outputs a dump of the exception frame to the active console.
 func (f *Frame) Print() {
-	early.Printf("RIP = %16x CS  = %16x\n", f.RIP, f.CS)
-	early.Printf("RSP = %16x SS  = %16x\n", f.RSP, f.SS)
-	early.Printf("RFL = %16x\n", f.RFlags)
+	kfmt.Printf("RIP = %16x CS  = %16x\n", f.RIP, f.CS)
+	kfmt.Printf("RSP = %16x SS  = %16x\n", f.RSP, f.SS)
+	kfmt.Printf("RFL = %16x\n", f.RFlags)
 }

src/gopheros/kernel/irq/interrupt_amd64_test.go

@@ -2,14 +2,16 @@ package irq
 
 import (
 	"bytes"
-	"gopheros/kernel/driver/video/console"
-	"gopheros/kernel/hal"
+	"gopheros/kernel/kfmt"
 	"testing"
-	"unsafe"
 )
 
 func TestRegsPrint(t *testing.T) {
-	fb := mockTTY()
+	defer func() {
+		kfmt.SetOutputSink(nil)
+	}()
+	var buf bytes.Buffer
+
 	regs := Regs{
 		RAX: 1,
 		RBX: 2,
@@ -29,15 +31,20 @@ func TestRegsPrint(t *testing.T) {
 	}
 	regs.Print()
 
-	exp := "RAX = 0000000000000001 RBX = 0000000000000002\nRCX = 0000000000000003 RDX = 0000000000000004\nRSI = 0000000000000005 RDI = 0000000000000006\nRBP = 0000000000000007\nR8  = 0000000000000008 R9  = 0000000000000009\nR10 = 000000000000000a R11 = 000000000000000b\nR12 = 000000000000000c R13 = 000000000000000d\nR14 = 000000000000000e R15 = 000000000000000f"
+	exp := "RAX = 0000000000000001 RBX = 0000000000000002\nRCX = 0000000000000003 RDX = 0000000000000004\nRSI = 0000000000000005 RDI = 0000000000000006\nRBP = 0000000000000007\nR8  = 0000000000000008 R9  = 0000000000000009\nR10 = 000000000000000a R11 = 000000000000000b\nR12 = 000000000000000c R13 = 000000000000000d\nR14 = 000000000000000e R15 = 000000000000000f\n"
 
-	if got := readTTY(fb); got != exp {
+	kfmt.SetOutputSink(&buf)
+	if got := buf.String(); got != exp {
 		t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
 	}
 }
 
 func TestFramePrint(t *testing.T) {
-	fb := mockTTY()
+	defer func() {
+		kfmt.SetOutputSink(nil)
+	}()
+	var buf bytes.Buffer
+
 	frame := Frame{
 		RIP:    1,
 		CS:     2,
@@ -47,37 +54,11 @@ func TestFramePrint(t *testing.T) {
 	}
 	frame.Print()
 
-	exp := "RIP = 0000000000000001 CS  = 0000000000000002\nRSP = 0000000000000004 SS  = 0000000000000005\nRFL = 0000000000000003"
+	exp := "RIP = 0000000000000001 CS  = 0000000000000002\nRSP = 0000000000000004 SS  = 0000000000000005\nRFL = 0000000000000003\n"
 
-	if got := readTTY(fb); got != exp {
+	kfmt.SetOutputSink(&buf)
+	if got := buf.String(); got != exp {
 		t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
 	}
 
 }
-
-func readTTY(fb []byte) string {
-	var buf bytes.Buffer
-	for i := 0; i < len(fb); i += 2 {
-		ch := fb[i]
-		if ch == 0 {
-			if i+2 < len(fb) && fb[i+2] != 0 {
-				buf.WriteByte('\n')
-			}
-			continue
-		}
-
-		buf.WriteByte(ch)
-	}
-
-	return buf.String()
-}
-
-func mockTTY() []byte {
-	// Mock a tty to handle early.Printf output
-	mockConsoleFb := make([]byte, 160*25)
-	mockConsole := &console.Ega{}
-	mockConsole.Init(80, 25, uintptr(unsafe.Pointer(&mockConsoleFb[0])))
-	hal.ActiveTerminal.AttachTo(mockConsole)
-
-	return mockConsoleFb
-}

src/gopheros/kernel/kfmt/fmt.go

@@ -1,20 +1,48 @@
-package early
+package kfmt
 
-import "gopheros/kernel/hal"
+import (
+	"io"
+	"unsafe"
+)
+
+// maxBufSize defines the buffer size for formatting numbers.
+const maxBufSize = 32
 
 var (
 	errMissingArg   = []byte("(MISSING)")
 	errWrongArgType = []byte("%!(WRONGTYPE)")
 	errNoVerb       = []byte("%!(NOVERB)")
 	errExtraArg     = []byte("%!(EXTRA)")
-	padding         = byte(' ')
 	trueValue       = []byte("true")
 	falseValue      = []byte("false")
+
+	numFmtBuf = []byte("012345678901234567890123456789012")
+
+	// singleByte is used as a shared buffer for passing single characters
+	// to doWrite.
+	singleByte = []byte(" ")
+
+	// earlyPrintBuffer is a ring buffer that stores Printf output before the
+	// console and TTYs are initialized.
+	earlyPrintBuffer ringBuffer
+
+	// outputSink is a io.Writer where Printf will send its output. If set
+	// to nil, then the output will be redirected to the earlyPrintBuffer.
+	outputSink io.Writer
 )
 
-// Printf provides a minimal Printf implementation that can be used before the
-// Go runtime has been properly initialized. This version of printf does not
-// allocate any memory and uses hal.ActiveTerminal for its output.
+// SetOutputSink sets the default target for calls to Printf to w and copies
+// any data accumulated in the earlyPrintBuffer to itt .
+func SetOutputSink(w io.Writer) {
+	outputSink = w
+	if w != nil {
+		io.Copy(w, &earlyPrintBuffer)
+	}
+}
+
+// Printf provides a minimal Printf implementation that can be safely  used
+// before the Go runtime has been properly initialized. This implementation
+// does not allocate any memory.
 //
 // Similar to fmt.Printf, this version of printf supports the following subset
 // of formatting verbs:
@@ -46,7 +74,17 @@ var (
 // starts generating calls to runtime.convT2E (which calls runtime.newobject)
 // when assembling the argument slice which obviously will crash the kernel since
 // memory management is not yet available.
+//
+// The output of Printf is written to the currently active TTY. If no TTY is
+// available, then the output is buffered into a ring-buffer and can be
+// retrieved by a call to FlushRingBuffer.
 func Printf(format string, args ...interface{}) {
+	Fprintf(outputSink, format, args...)
+}
+
+// Fprintf behaves exactly like Printf but it writes the formatted output to
+// the specified io.Writer.
+func Fprintf(w io.Writer, format string, args ...interface{}) {
 	var (
 		nextCh                       byte
 		nextArgIndex                 int
@@ -62,8 +100,11 @@ func Printf(format string, args ...interface{}) {
 		}
 
 		if blockStart < blockEnd {
+			// passing format[blockStart:blockEnd] to doWrite triggers a
+			// memory allocation so we need to do this one byte at a time.
 			for i := blockStart; i < blockEnd; i++ {
-				hal.ActiveTerminal.WriteByte(format[i])
+				singleByte[0] = format[i]
+				doWrite(w, singleByte)
 			}
 		}
 
@@ -75,7 +116,8 @@ func Printf(format string, args ...interface{}) {
 			nextCh = format[blockEnd]
 			switch {
 			case nextCh == '%':
-				hal.ActiveTerminal.Write([]byte{'%'})
+				singleByte[0] = '%'
+				doWrite(w, singleByte)
 				break parseFmt
 			case nextCh >= '0' && nextCh <= '9':
 				padLen = (padLen * 10) + int(nextCh-'0')
@@ -83,21 +125,21 @@ func Printf(format string, args ...interface{}) {
 			case nextCh == 'd' || nextCh == 'x' || nextCh == 'o' || nextCh == 's' || nextCh == 't':
 				// Run out of args to print
 				if nextArgIndex >= len(args) {
-					hal.ActiveTerminal.Write(errMissingArg)
+					doWrite(w, errMissingArg)
 					break parseFmt
 				}
 
 				switch nextCh {
 				case 'o':
-					fmtInt(args[nextArgIndex], 8, padLen)
+					fmtInt(w, args[nextArgIndex], 8, padLen)
 				case 'd':
-					fmtInt(args[nextArgIndex], 10, padLen)
+					fmtInt(w, args[nextArgIndex], 10, padLen)
 				case 'x':
-					fmtInt(args[nextArgIndex], 16, padLen)
+					fmtInt(w, args[nextArgIndex], 16, padLen)
 				case 's':
-					fmtString(args[nextArgIndex], padLen)
+					fmtString(w, args[nextArgIndex], padLen)
 				case 't':
-					fmtBool(args[nextArgIndex])
+					fmtBool(w, args[nextArgIndex])
 				}
 
 				nextArgIndex++
@@ -105,80 +147,87 @@ func Printf(format string, args ...interface{}) {
 			}
 
 			// reached end of formatting string without finding a verb
-			hal.ActiveTerminal.Write(errNoVerb)
+			doWrite(w, errNoVerb)
 		}
 		blockStart, blockEnd = blockEnd+1, blockEnd+1
 	}
 
 	if blockStart != blockEnd {
+		// passing format[blockStart:blockEnd] to doWrite triggers a
+		// memory allocation so we need to do this one byte at a time.
 		for i := blockStart; i < blockEnd; i++ {
-			hal.ActiveTerminal.WriteByte(format[i])
+			singleByte[0] = format[i]
+			doWrite(w, singleByte)
 		}
 	}
 
 	// Check for unused args
 	for ; nextArgIndex < len(args); nextArgIndex++ {
-		hal.ActiveTerminal.Write(errExtraArg)
+		doWrite(w, errExtraArg)
 	}
 }
 
-// fmtBool prints a formatted version of boolean value v using hal.ActiveTerminal
-// for its output.
-func fmtBool(v interface{}) {
+// fmtBool prints a formatted version of boolean value v.
+func fmtBool(w io.Writer, v interface{}) {
 	switch bVal := v.(type) {
 	case bool:
 		switch bVal {
 		case true:
-			hal.ActiveTerminal.Write(trueValue)
+			doWrite(w, trueValue)
 		case false:
-			hal.ActiveTerminal.Write(falseValue)
+			doWrite(w, falseValue)
 		}
 	default:
-		hal.ActiveTerminal.Write(errWrongArgType)
+		doWrite(w, errWrongArgType)
 		return
 	}
 }
 
-// fmtString prints a formatted version of string or []byte value v, applying the
-// padding specified by padLen. This function uses hal.ActiveTerminal for its
-// output.
-func fmtString(v interface{}, padLen int) {
+// fmtString prints a formatted version of string or []byte value v, applying
+// the padding specified by padLen.
+func fmtString(w io.Writer, v interface{}, padLen int) {
 	switch castedVal := v.(type) {
 	case string:
-		fmtRepeat(padding, padLen-len(castedVal))
+		fmtRepeat(w, ' ', padLen-len(castedVal))
+		// converting the string to a byte slice triggers a memory allocation
+		// so we need to do this one byte at a time.
 		for i := 0; i < len(castedVal); i++ {
-			hal.ActiveTerminal.WriteByte(castedVal[i])
+			singleByte[0] = castedVal[i]
+			doWrite(w, singleByte)
 		}
 	case []byte:
-		fmtRepeat(padding, padLen-len(castedVal))
-		hal.ActiveTerminal.Write(castedVal)
+		fmtRepeat(w, ' ', padLen-len(castedVal))
+		doWrite(w, castedVal)
 	default:
-		hal.ActiveTerminal.Write(errWrongArgType)
+		doWrite(w, errWrongArgType)
 	}
 }
 
-// fmtRepeat writes count bytes with value ch to the hal.ActiveTerminal.
-func fmtRepeat(ch byte, count int) {
+// fmtRepeat writes count bytes with value ch.
+func fmtRepeat(w io.Writer, ch byte, count int) {
+	singleByte[0] = ch
 	for i := 0; i < count; i++ {
-		hal.ActiveTerminal.WriteByte(ch)
+		doWrite(w, singleByte)
 	}
 }
 
-// fmtInt prints out a formatted version of v in the requested base, applying the
-// padding specified by padLen. This function uses hal.ActiveTerminal for its
-// output, supports all built-in signed and unsigned integer types and supports
-// base 8, 10 and 16 output.
-func fmtInt(v interface{}, base, padLen int) {
+// fmtInt prints out a formatted version of v in the requested base, applying
+// the padding specified by padLen. This function supports all built-in signed
+// and unsigned integer types and base 8, 10 and 16 output.
+func fmtInt(w io.Writer, v interface{}, base, padLen int) {
 	var (
 		sval             int64
 		uval             uint64
 		divider          uint64
 		remainder        uint64
-		buf              [20]byte
 		padCh            byte
 		left, right, end int
 	)
 
+	if padLen >= maxBufSize {
+		padLen = maxBufSize - 1
+	}
+
 	switch base {
 	case 8:
 		divider = 8
@@ -213,7 +262,7 @@ func fmtInt(v interface{}, base, padLen int) {
 	case int:
 		sval = int64(v.(int))
 	default:
-		hal.ActiveTerminal.Write(errWrongArgType)
+		doWrite(w, errWrongArgType)
 		return
 	}
 
@@ -224,13 +273,13 @@ func fmtInt(v interface{}, base, padLen int) {
 		uval = uint64(sval)
 	}
 
-	for {
+	for right < maxBufSize {
 		remainder = uval % divider
 		if remainder < 10 {
-			buf[right] = byte(remainder) + '0'
+			numFmtBuf[right] = byte(remainder) + '0'
 		} else {
 			// map values from 10 to 15 -> a-f
-			buf[right] = byte(remainder-10) + 'a'
+			numFmtBuf[right] = byte(remainder-10) + 'a'
 		}
 
 		right++
@@ -243,27 +292,55 @@ func fmtInt(v interface{}, base, padLen int) {
 
 	// Apply padding if required
 	for ; right-left < padLen; right++ {
-		buf[right] = padCh
+		numFmtBuf[right] = padCh
 	}
 
 	// Apply negative sign to the rightmost blank character (if using enough padding);
 	// otherwise append the sign as a new char
 	if sval < 0 {
-		for end = right - 1; buf[end] == ' '; end-- {
+		for end = right - 1; numFmtBuf[end] == ' '; end-- {
 		}
 
 		if end == right-1 {
 			right++
 		}
 
-		buf[end+1] = '-'
+		numFmtBuf[end+1] = '-'
 	}
 
 	// Reverse in place
 	end = right
 	for right = right - 1; left < right; left, right = left+1, right-1 {
-		buf[left], buf[right] = buf[right], buf[left]
+		numFmtBuf[left], numFmtBuf[right] = numFmtBuf[right], numFmtBuf[left]
 	}
 
-	hal.ActiveTerminal.Write(buf[0:end])
+	doWrite(w, numFmtBuf[0:end])
+}
+
+// doWrite is a proxy that uses the runtime.noescape hack to hide p from the
+// compiler's escape analysis. Without this hack, the compiler cannot properly
+// detect that p does not escape (due to the call to the yet unknown outputSink
+// io.Writer) and plays it safe by flagging it as escaping. This causes all
+// calls to Printf to call runtime.convT2E which triggers a memory allocation
+// causing the kernel to crash if a call to Printf is made before the Go
+// allocator is initialized.
+func doWrite(w io.Writer, p []byte) {
+	doRealWrite(w, noEscape(unsafe.Pointer(&p)))
+}
+
+func doRealWrite(w io.Writer, bufPtr unsafe.Pointer) {
+	p := *(*[]byte)(bufPtr)
+	if w != nil {
+		w.Write(p)
+	} else {
+		earlyPrintBuffer.Write(p)
+	}
+}
+
+// noEscape hides a pointer from escape analysis. This function is copied over
+// from runtime/stubs.go
+//go:nosplit
+func noEscape(p unsafe.Pointer) unsafe.Pointer {
+	x := uintptr(p)
+	return unsafe.Pointer(x ^ 0)
 }

src/gopheros/kernel/kfmt/fmt_test.go

@@ -1,31 +1,20 @@
-package early
+package kfmt
 
 import (
 	"bytes"
-	"gopheros/kernel/driver/tty"
-	"gopheros/kernel/driver/video/console"
-	"gopheros/kernel/hal"
+	"fmt"
+	"strings"
 	"testing"
-	"unsafe"
 )
 
 func TestPrintf(t *testing.T) {
-	origTerm := hal.ActiveTerminal
 	defer func() {
-		hal.ActiveTerminal = origTerm
+		outputSink = nil
 	}()
 
 	// mute vet warnings about malformed printf formatting strings
 	printfn := Printf
 
-	ega := &console.Ega{}
-	fb := make([]uint8, 160*25)
-	ega.Init(80, 25, uintptr(unsafe.Pointer(&fb[0])))
-
-	vt := &tty.Vt{}
-	vt.AttachTo(ega)
-	hal.ActiveTerminal = vt
-
 	specs := []struct {
 		fn        func()
 		expOutput string
@@ -124,6 +113,10 @@ func TestPrintf(t *testing.T) {
 			func() { printfn("int arg longer than padding: '%5x'", int(-0xbadf00d)) },
 			"int arg longer than padding: '-badf00d'",
 		},
+		{
+			func() { printfn("padding longer than maxBufSize '%128x'", int(-0xbadf00d)) },
+			fmt.Sprintf("padding longer than maxBufSize '-%sbadf00d'", strings.Repeat("0", maxBufSize-8)),
+		},
 		// multiple arguments
 		{
 			func() { printfn("%%%s%d%t", "foo", 123, true) },
@@ -156,25 +149,42 @@ func TestPrintf(t *testing.T) {
 		},
 	}
 
-	for specIndex, spec := range specs {
-		for index := 0; index < len(fb); index++ {
-			fb[index] = 0
-		}
-		vt.SetPosition(0, 0)
+	var buf bytes.Buffer
+	SetOutputSink(&buf)
 
+	for specIndex, spec := range specs {
+		buf.Reset()
 		spec.fn()
 
-		var buf bytes.Buffer
-		for index := 0; ; index += 2 {
-			if fb[index] == 0 {
-				break
-			}
-
-			buf.WriteByte(fb[index])
-		}
-
 		if got := buf.String(); got != spec.expOutput {
-			t.Errorf("[spec %d] expected to get %q; got %q", specIndex, spec.expOutput, got)
+			t.Errorf("[spec %d] expected to get\n%q\ngot:\n%q", specIndex, spec.expOutput, got)
 		}
 	}
 }
+
+func TestPrintfToRingBuffer(t *testing.T) {
+	defer func() {
+		outputSink = nil
+	}()
+
+	exp := "hello world"
+	Printf(exp)
+
+	var buf bytes.Buffer
+	SetOutputSink(&buf)
+
+	if got := buf.String(); got != exp {
+		t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
+	}
+}
+
+func TestFprintf(t *testing.T) {
+	var buf bytes.Buffer
+
+	exp := "hello world"
+	Fprintf(&buf, exp)
+
+	if got := buf.String(); got != exp {
+		t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
+	}
+}

src/gopheros/kernel/kfmt/panic.go

@@ -1,15 +1,15 @@
-package kernel
+package kfmt
 
 import (
+	"gopheros/kernel"
 	"gopheros/kernel/cpu"
-	"gopheros/kernel/kfmt/early"
 )
 
 var (
 	// cpuHaltFn is mocked by tests and is automatically inlined by the compiler.
 	cpuHaltFn = cpu.Halt
 
-	errRuntimePanic = &Error{Module: "rt", Message: "unknown cause"}
+	errRuntimePanic = &kernel.Error{Module: "rt", Message: "unknown cause"}
 )
 
 // Panic outputs the supplied error (if not nil) to the console and halts the
@@ -17,10 +17,10 @@ var (
 // for calls to panic() (resolved via runtime.gopanic)
 //go:redirect-from runtime.gopanic
 func Panic(e interface{}) {
-	var err *Error
+	var err *kernel.Error
 
 	switch t := e.(type) {
-	case *Error:
+	case *kernel.Error:
 		err = t
 	case string:
 		panicString(t)
@@ -30,12 +30,12 @@ func Panic(e interface{}) {
 		err = errRuntimePanic
 	}
 
-	early.Printf("\n-----------------------------------\n")
+	Printf("\n-----------------------------------\n")
 	if err != nil {
-		early.Printf("[%s] unrecoverable error: %s\n", err.Module, err.Message)
+		Printf("[%s] unrecoverable error: %s\n", err.Module, err.Message)
 	}
-	early.Printf("*** kernel panic: system halted ***")
-	early.Printf("\n-----------------------------------\n")
+	Printf("*** kernel panic: system halted ***")
+	Printf("\n-----------------------------------\n")
 
 	cpuHaltFn()
 }

src/gopheros/kernel/kfmt/panic_test.go

@@ -1,20 +1,22 @@
-package kernel
+package kfmt
 
 import (
 	"bytes"
 	"errors"
+	"gopheros/kernel"
 	"gopheros/kernel/cpu"
-	"gopheros/kernel/driver/video/console"
-	"gopheros/kernel/hal"
 	"testing"
-	"unsafe"
 )
 
 func TestPanic(t *testing.T) {
 	defer func() {
 		cpuHaltFn = cpu.Halt
+		SetOutputSink(nil)
 	}()
 
+	var buf bytes.Buffer
+	SetOutputSink(&buf)
+
 	var cpuHaltCalled bool
 	cpuHaltFn = func() {
 		cpuHaltCalled = true
@@ -22,14 +24,14 @@ func TestPanic(t *testing.T) {
 
 	t.Run("with *kernel.Error", func(t *testing.T) {
 		cpuHaltCalled = false
-		fb := mockTTY()
-		err := &Error{Module: "test", Message: "panic test"}
+		buf.Reset()
+		err := &kernel.Error{Module: "test", Message: "panic test"}
 
 		Panic(err)
 
-		exp := "\n-----------------------------------\n[test] unrecoverable error: panic test\n*** kernel panic: system halted ***\n-----------------------------------"
+		exp := "\n-----------------------------------\n[test] unrecoverable error: panic test\n*** kernel panic: system halted ***\n-----------------------------------\n"
 
-		if got := readTTY(fb); got != exp {
+		if got := buf.String(); got != exp {
 			t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
 		}
 
@@ -40,14 +42,14 @@ func TestPanic(t *testing.T) {
 
 	t.Run("with error", func(t *testing.T) {
 		cpuHaltCalled = false
-		fb := mockTTY()
+		buf.Reset()
 		err := errors.New("go error")
 
 		Panic(err)
 
-		exp := "\n-----------------------------------\n[rt] unrecoverable error: go error\n*** kernel panic: system halted ***\n-----------------------------------"
+		exp := "\n-----------------------------------\n[rt] unrecoverable error: go error\n*** kernel panic: system halted ***\n-----------------------------------\n"
 
-		if got := readTTY(fb); got != exp {
+		if got := buf.String(); got != exp {
 			t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
 		}
 
@@ -58,14 +60,14 @@ func TestPanic(t *testing.T) {
 
 	t.Run("with string", func(t *testing.T) {
 		cpuHaltCalled = false
-		fb := mockTTY()
+		buf.Reset()
 		err := "string error"
 
 		Panic(err)
 
-		exp := "\n-----------------------------------\n[rt] unrecoverable error: string error\n*** kernel panic: system halted ***\n-----------------------------------"
+		exp := "\n-----------------------------------\n[rt] unrecoverable error: string error\n*** kernel panic: system halted ***\n-----------------------------------\n"
 
-		if got := readTTY(fb); got != exp {
+		if got := buf.String(); got != exp {
 			t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
 		}
 
@@ -76,13 +78,13 @@ func TestPanic(t *testing.T) {
 
 	t.Run("without error", func(t *testing.T) {
 		cpuHaltCalled = false
-		fb := mockTTY()
+		buf.Reset()
 
 		Panic(nil)
 
-		exp := "\n-----------------------------------\n*** kernel panic: system halted ***\n-----------------------------------"
+		exp := "\n-----------------------------------\n*** kernel panic: system halted ***\n-----------------------------------\n"
 
-		if got := readTTY(fb); got != exp {
+		if got := buf.String(); got != exp {
 			t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
 		}
 
@@ -91,30 +93,3 @@ func TestPanic(t *testing.T) {
 		}
 	})
 }
-
-func readTTY(fb []byte) string {
-	var buf bytes.Buffer
-	for i := 0; i < len(fb); i += 2 {
-		ch := fb[i]
-		if ch == 0 {
-			if i+2 < len(fb) && fb[i+2] != 0 {
-				buf.WriteByte('\n')
-			}
-			continue
-		}
-
-		buf.WriteByte(ch)
-	}
-
-	return buf.String()
-}
-
-func mockTTY() []byte {
-	// Mock a tty to handle early.Printf output
-	mockConsoleFb := make([]byte, 160*25)
-	mockConsole := &console.Ega{}
-	mockConsole.Init(80, 25, uintptr(unsafe.Pointer(&mockConsoleFb[0])))
-	hal.ActiveTerminal.AttachTo(mockConsole)
-
-	return mockConsoleFb
-}

src/gopheros/kernel/kfmt/ringbuf.go

@@ -0,0 +1,65 @@
+package kfmt
+
+import "io"
+
+// ringBufferSize defines size of the ring buffer that buffers early Printf
+// output. Its default size is selected so it can buffer the contents of a
+// standard 80*25 text-mode console. The ring buffer size must always be a
+// power of 2.
+const ringBufferSize = 2048
+
+// ringBuffer models a ring buffer of size ringBufferSize. This buffer is used
+// for capturing the output of Printf before the tty and console systems are
+// initialized.
+type ringBuffer struct {
+	buffer         [ringBufferSize]byte
+	rIndex, wIndex int
+}
+
+// Write writes len(p) bytes from p to the ringBuffer.
+func (rb *ringBuffer) Write(p []byte) (int, error) {
+	for _, b := range p {
+		rb.buffer[rb.wIndex] = b
+		rb.wIndex = (rb.wIndex + 1) & (ringBufferSize - 1)
+		if rb.rIndex == rb.wIndex {
+			rb.rIndex = (rb.rIndex + 1) & (ringBufferSize - 1)
+		}
+	}
+
+	return len(p), nil
+}
+
+// Read reads up to len(p) bytes into p. It returns the number of bytes read (0
+// <= n <= len(p)) and any error encountered.
+func (rb *ringBuffer) Read(p []byte) (n int, err error) {
+	switch {
+	case rb.rIndex < rb.wIndex:
+		// read up to min(wIndex - rIndex, len(p)) bytes
+		n = rb.wIndex - rb.rIndex
+		if pLen := len(p); pLen < n {
+			n = pLen
+		}
+
+		copy(p, rb.buffer[rb.rIndex:rb.rIndex+n])
+		rb.rIndex += n
+
+		return n, nil
+	case rb.rIndex > rb.wIndex:
+		// Read up to min(len(buf) - rIndex, len(p)) bytes
+		n = len(rb.buffer) - rb.rIndex
+		if pLen := len(p); pLen < n {
+			n = pLen
+		}
+
+		copy(p, rb.buffer[rb.rIndex:rb.rIndex+n])
+		rb.rIndex += n
+
+		if rb.rIndex == len(rb.buffer) {
+			rb.rIndex = 0
+		}
+
+		return n, nil
+	default: // rIndex == wIndex
+		return 0, io.EOF
+	}
+}

src/gopheros/kernel/kfmt/ringbuf_test.go

@@ -0,0 +1,96 @@
+package kfmt
+
+import (
+	"bytes"
+	"io"
+	"testing"
+)
+
+func TestRingBuffer(t *testing.T) {
+	var (
+		buf    bytes.Buffer
+		expStr = "the big brown fox jumped over the lazy dog"
+		rb     ringBuffer
+	)
+
+	t.Run("read/write", func(t *testing.T) {
+		rb.wIndex = 0
+		rb.rIndex = 0
+		n, err := rb.Write([]byte(expStr))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if n != len(expStr) {
+			t.Fatalf("expected to write %d bytes; wrote %d", len(expStr), n)
+		}
+
+		if got := readByteByByte(&buf, &rb); got != expStr {
+			t.Fatalf("expected to read %q; got %q", expStr, got)
+		}
+	})
+
+	t.Run("write moves read pointer", func(t *testing.T) {
+		rb.wIndex = ringBufferSize - 1
+		rb.rIndex = 0
+		_, err := rb.Write([]byte{'!'})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if exp := 1; rb.rIndex != exp {
+			t.Fatalf("expected write to push rIndex to %d; got %d", exp, rb.rIndex)
+		}
+	})
+
+	t.Run("wIndex < rIndex", func(t *testing.T) {
+		rb.wIndex = ringBufferSize - 2
+		rb.rIndex = ringBufferSize - 2
+		n, err := rb.Write([]byte(expStr))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if n != len(expStr) {
+			t.Fatalf("expected to write %d bytes; wrote %d", len(expStr), n)
+		}
+
+		if got := readByteByByte(&buf, &rb); got != expStr {
+			t.Fatalf("expected to read %q; got %q", expStr, got)
+		}
+	})
+
+	t.Run("with io.WriteTo", func(t *testing.T) {
+		rb.wIndex = ringBufferSize - 2
+		rb.rIndex = ringBufferSize - 2
+		n, err := rb.Write([]byte(expStr))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if n != len(expStr) {
+			t.Fatalf("expected to write %d bytes; wrote %d", len(expStr), n)
+		}
+
+		var buf bytes.Buffer
+		io.Copy(&buf, &rb)
+
+		if got := buf.String(); got != expStr {
+			t.Fatalf("expected to read %q; got %q", expStr, got)
+		}
+	})
+}
+
+func readByteByByte(buf *bytes.Buffer, r io.Reader) string {
+	buf.Reset()
+	var b = make([]byte, 1)
+	for {
+		_, err := r.Read(b)
+		if err == io.EOF {
+			break
+		}
+
+		buf.Write(b)
+	}
+	return buf.String()
+}

src/gopheros/kernel/kmain/kmain.go

@@ -5,6 +5,7 @@ import (
 	"gopheros/kernel/goruntime"
 	"gopheros/kernel/hal"
 	"gopheros/kernel/hal/multiboot"
+	"gopheros/kernel/kfmt"
 	"gopheros/kernel/mem/pmm/allocator"
 	"gopheros/kernel/mem/vmm"
 )
@@ -27,9 +28,6 @@ var (
 func Kmain(multibootInfoPtr, kernelStart, kernelEnd uintptr) {
 	multiboot.SetInfoPtr(multibootInfoPtr)
 
-	hal.InitTerminal()
-	hal.ActiveTerminal.Clear()
-
 	var err *kernel.Error
 	if err = allocator.Init(kernelStart, kernelEnd); err != nil {
 		panic(err)
@@ -39,7 +37,10 @@ func Kmain(multibootInfoPtr, kernelStart, kernelEnd uintptr) {
 		panic(err)
 	}
 
-	// Use kernel.Panic instead of panic to prevent the compiler from
+	// Detect and initialize hardware
+	hal.DetectHardware()
+
+	// Use kfmt.Panic instead of panic to prevent the compiler from
 	// treating kernel.Panic as dead-code and eliminating it.
-	kernel.Panic(errKmainReturned)
+	kfmt.Panic(errKmainReturned)
 }

src/gopheros/kernel/mem/pmm/allocator/bitmap_allocator.go

@@ -3,7 +3,7 @@ package allocator
 import (
 	"gopheros/kernel"
 	"gopheros/kernel/hal/multiboot"
-	"gopheros/kernel/kfmt/early"
+	"gopheros/kernel/kfmt"
 	"gopheros/kernel/mem"
 	"gopheros/kernel/mem/pmm"
 	"gopheros/kernel/mem/vmm"
@@ -234,7 +234,7 @@ func (alloc *BitmapAllocator) reserveEarlyAllocatorFrames() {
 }
 
 func (alloc *BitmapAllocator) printStats() {
-	early.Printf(
+	kfmt.Printf(
 		"[bitmap_alloc] page stats: free: %d/%d (%d reserved)\n",
 		alloc.totalPages-alloc.reservedPages,
 		alloc.totalPages,

src/gopheros/kernel/mem/pmm/allocator/bitmap_allocator_test.go

@@ -406,7 +406,6 @@ func TestAllocatorPackageInit(t *testing.T) {
 			return uintptr(unsafe.Pointer(&physMem[0])), nil
 		}
 
-		mockTTY()
 		if err := Init(0x100000, 0x1fa7c8); err != nil {
 			t.Fatal(err)
 		}

src/gopheros/kernel/mem/pmm/allocator/bootmem.go

@@ -3,7 +3,7 @@ package allocator
 import (
 	"gopheros/kernel"
 	"gopheros/kernel/hal/multiboot"
-	"gopheros/kernel/kfmt/early"
+	"gopheros/kernel/kfmt"
 	"gopheros/kernel/mem"
 	"gopheros/kernel/mem/pmm"
 )
@@ -117,19 +117,19 @@ func (alloc *bootMemAllocator) AllocFrame() (pmm.Frame, *kernel.Error) {
 // printMemoryMap scans the memory region information provided by the
 // bootloader and prints out the system's memory map.
 func (alloc *bootMemAllocator) printMemoryMap() {
-	early.Printf("[boot_mem_alloc] system memory map:\n")
+	kfmt.Printf("[boot_mem_alloc] system memory map:\n")
 	var totalFree mem.Size
 	multiboot.VisitMemRegions(func(region *multiboot.MemoryMapEntry) bool {
-		early.Printf("\t[0x%10x - 0x%10x], size: %10d, type: %s\n", region.PhysAddress, region.PhysAddress+region.Length, region.Length, region.Type.String())
+		kfmt.Printf("\t[0x%10x - 0x%10x], size: %10d, type: %s\n", region.PhysAddress, region.PhysAddress+region.Length, region.Length, region.Type.String())
 
 		if region.Type == multiboot.MemAvailable {
 			totalFree += mem.Size(region.Length)
 		}
 		return true
 	})
-	early.Printf("[boot_mem_alloc] available memory: %dKb\n", uint64(totalFree/mem.Kb))
-	early.Printf("[boot_mem_alloc] kernel loaded at 0x%x - 0x%x\n", alloc.kernelStartAddr, alloc.kernelEndAddr)
-	early.Printf("[boot_mem_alloc] size: %d bytes, reserved pages: %d\n",
+	kfmt.Printf("[boot_mem_alloc] available memory: %dKb\n", uint64(totalFree/mem.Kb))
+	kfmt.Printf("[boot_mem_alloc] kernel loaded at 0x%x - 0x%x\n", alloc.kernelStartAddr, alloc.kernelEndAddr)
+	kfmt.Printf("[boot_mem_alloc] size: %d bytes, reserved pages: %d\n",
 		uint64(alloc.kernelEndAddr-alloc.kernelStartAddr),
 		uint64(alloc.kernelEndFrame-alloc.kernelStartFrame+1),
 	)

src/gopheros/kernel/mem/pmm/allocator/bootmem_test.go

@@ -1,8 +1,6 @@
 package allocator
 
 import (
-	"gopheros/kernel/driver/video/console"
-	"gopheros/kernel/hal"
 	"gopheros/kernel/hal/multiboot"
 	"testing"
 	"unsafe"
@@ -118,13 +116,3 @@ var (
 		24, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 	}
 )
-
-func mockTTY() []byte {
-	// Mock a tty to handle early.Printf output
-	mockConsoleFb := make([]byte, 160*25)
-	mockConsole := &console.Ega{}
-	mockConsole.Init(80, 25, uintptr(unsafe.Pointer(&mockConsoleFb[0])))
-	hal.ActiveTerminal.AttachTo(mockConsole)
-
-	return mockConsoleFb
-}

src/gopheros/kernel/mem/vmm/translate_test.go

@@ -61,12 +61,3 @@ func TestTranslateAmd64(t *testing.T) {
 		}
 	}
 }
-
-/*
-	phys, err := vmm.Translate(uintptr(100 * mem.Mb))
-	if err != nil {
-		early.Printf("err: %s\n", err.Error())
-	} else {
-		early.Printf("phys: 0x%x\n", phys)
-	}
-*/

src/gopheros/kernel/mem/vmm/vmm.go

@@ -4,7 +4,7 @@ import (
 	"gopheros/kernel"
 	"gopheros/kernel/cpu"
 	"gopheros/kernel/irq"
-	"gopheros/kernel/kfmt/early"
+	"gopheros/kernel/kfmt"
 	"gopheros/kernel/mem"
 	"gopheros/kernel/mem/pmm"
 )
@@ -83,27 +83,27 @@ func pageFaultHandler(errorCode uint64, frame *irq.Frame, regs *irq.Regs) {
 }
 
 func nonRecoverablePageFault(faultAddress uintptr, errorCode uint64, frame *irq.Frame, regs *irq.Regs, err *kernel.Error) {
-	early.Printf("\nPage fault while accessing address: 0x%16x\nReason: ", faultAddress)
+	kfmt.Printf("\nPage fault while accessing address: 0x%16x\nReason: ", faultAddress)
 	switch {
 	case errorCode == 0:
-		early.Printf("read from non-present page")
+		kfmt.Printf("read from non-present page")
 	case errorCode == 1:
-		early.Printf("page protection violation (read)")
+		kfmt.Printf("page protection violation (read)")
 	case errorCode == 2:
-		early.Printf("write to non-present page")
+		kfmt.Printf("write to non-present page")
 	case errorCode == 3:
-		early.Printf("page protection violation (write)")
+		kfmt.Printf("page protection violation (write)")
 	case errorCode == 4:
-		early.Printf("page-fault in user-mode")
+		kfmt.Printf("page-fault in user-mode")
 	case errorCode == 8:
-		early.Printf("page table has reserved bit set")
+		kfmt.Printf("page table has reserved bit set")
 	case errorCode == 16:
-		early.Printf("instruction fetch")
+		kfmt.Printf("instruction fetch")
 	default:
-		early.Printf("unknown")
+		kfmt.Printf("unknown")
 	}
 
-	early.Printf("\n\nRegisters:\n")
+	kfmt.Printf("\n\nRegisters:\n")
 	regs.Print()
 	frame.Print()
 
@@ -112,8 +112,8 @@ func nonRecoverablePageFault(faultAddress uintptr, errorCode uint64, frame *irq.
 }
 
 func generalProtectionFaultHandler(_ uint64, frame *irq.Frame, regs *irq.Regs) {
-	early.Printf("\nGeneral protection fault while accessing address: 0x%x\n", readCR2Fn())
-	early.Printf("Registers:\n")
+	kfmt.Printf("\nGeneral protection fault while accessing address: 0x%x\n", readCR2Fn())
+	kfmt.Printf("Registers:\n")
 	regs.Print()
 	frame.Print()
 

src/gopheros/kernel/mem/vmm/vmm_test.go

@@ -5,9 +5,8 @@ import (
 	"fmt"
 	"gopheros/kernel"
 	"gopheros/kernel/cpu"
-	"gopheros/kernel/driver/video/console"
-	"gopheros/kernel/hal"
 	"gopheros/kernel/irq"
+	"gopheros/kernel/kfmt"
 	"gopheros/kernel/mem"
 	"gopheros/kernel/mem/pmm"
 	"strings"
@@ -54,8 +53,6 @@ func TestRecoverablePageFault(t *testing.T) {
 		{FlagPresent | FlagCopyOnWrite, nil, nil, false},
 	}
 
-	mockTTY()
-
 	ptePtrFn = func(entry uintptr) unsafe.Pointer { return unsafe.Pointer(&pageEntry) }
 	readCR2Fn = func() uint64 { return uint64(uintptr(unsafe.Pointer(&origPage[0]))) }
 	unmapFn = func(_ Page) *kernel.Error { return nil }
@@ -102,6 +99,10 @@ func TestRecoverablePageFault(t *testing.T) {
 }
 
 func TestNonRecoverablePageFault(t *testing.T) {
+	defer func() {
+		kfmt.SetOutputSink(nil)
+	}()
+
 	specs := []struct {
 		errCode   uint64
 		expReason string
@@ -143,19 +144,21 @@ func TestNonRecoverablePageFault(t *testing.T) {
 	var (
 		regs  irq.Regs
 		frame irq.Frame
+		buf   bytes.Buffer
 	)
 
+	kfmt.SetOutputSink(&buf)
 	for specIndex, spec := range specs {
 		t.Run(fmt.Sprint(specIndex), func(t *testing.T) {
+			buf.Reset()
 			defer func() {
 				if err := recover(); err != errUnrecoverableFault {
 					t.Errorf("expected a panic with errUnrecoverableFault; got %v", err)
 				}
 			}()
-			fb := mockTTY()
 
 			nonRecoverablePageFault(0xbadf00d000, spec.errCode, &frame, &regs, errUnrecoverableFault)
-			if got := readTTY(fb); !strings.Contains(got, spec.expReason) {
+			if got := buf.String(); !strings.Contains(got, spec.expReason) {
 				t.Errorf("expected reason %q; got output:\n%q", spec.expReason, got)
 			}
 		})
@@ -182,7 +185,6 @@ func TestGPtHandler(t *testing.T) {
 		}
 	}()
 
-	mockTTY()
 	generalProtectionFaultHandler(0, &frame, &regs)
 }
 
@@ -252,30 +254,3 @@ func TestInit(t *testing.T) {
 		}
 	})
 }
-
-func readTTY(fb []byte) string {
-	var buf bytes.Buffer
-	for i := 0; i < len(fb); i += 2 {
-		ch := fb[i]
-		if ch == 0 {
-			if i+2 < len(fb) && fb[i+2] != 0 {
-				buf.WriteByte('\n')
-			}
-			continue
-		}
-
-		buf.WriteByte(ch)
-	}
-
-	return buf.String()
-}
-
-func mockTTY() []byte {
-	// Mock a tty to handle early.Printf output
-	mockConsoleFb := make([]byte, 160*25)
-	mockConsole := &console.Ega{}
-	mockConsole.Init(80, 25, uintptr(unsafe.Pointer(&mockConsoleFb[0])))
-	hal.ActiveTerminal.AttachTo(mockConsole)
-
-	return mockConsoleFb
-}