Make LCD button input more efficient

gen/genlookup.c

@@ -0,0 +1,107 @@
+/*
+ * Copyright (C) 2012 Southern Storm Software, Pty Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+// Utility for generating the button mapping table in FreetronicsLCD.cpp.
+
+#include <stdio.h>
+
+#define LCD_BUTTON_NONE         0
+#define LCD_BUTTON_LEFT         1
+#define LCD_BUTTON_RIGHT        2
+#define LCD_BUTTON_UP           3
+#define LCD_BUTTON_DOWN         4
+#define LCD_BUTTON_SELECT       5
+
+#define LCD_BUTTON_VALUE_GAP    10
+#define LCD_BUTTON_RIGHT_VALUE  0
+#define LCD_BUTTON_UP_VALUE     145
+#define LCD_BUTTON_DOWN_VALUE   329
+#define LCD_BUTTON_LEFT_VALUE   505
+#define LCD_BUTTON_SELECT_VALUE 741
+
+int main(int argc, char *argv[])
+{
+    char rawTest[1024];
+    int value, value2, value3, bits;
+    char button;
+
+    // Determine the actual values for each of the 1024 inputs.
+    for (value = 0; value < 1024; ++value) {
+        if (value < (LCD_BUTTON_RIGHT_VALUE + LCD_BUTTON_VALUE_GAP))
+            button = LCD_BUTTON_RIGHT;
+        else if (value >= (LCD_BUTTON_UP_VALUE - LCD_BUTTON_VALUE_GAP) &&
+                 value <= (LCD_BUTTON_UP_VALUE + LCD_BUTTON_VALUE_GAP))
+            button = LCD_BUTTON_UP;
+        else if (value >= (LCD_BUTTON_DOWN_VALUE - LCD_BUTTON_VALUE_GAP) &&
+                 value <= (LCD_BUTTON_DOWN_VALUE + LCD_BUTTON_VALUE_GAP))
+            button = LCD_BUTTON_DOWN;
+        else if (value >= (LCD_BUTTON_LEFT_VALUE - LCD_BUTTON_VALUE_GAP) &&
+                 value <= (LCD_BUTTON_LEFT_VALUE + LCD_BUTTON_VALUE_GAP))
+            button = LCD_BUTTON_LEFT;
+        else if (value >= (LCD_BUTTON_SELECT_VALUE - LCD_BUTTON_VALUE_GAP) &&
+                 value <= (LCD_BUTTON_SELECT_VALUE + LCD_BUTTON_VALUE_GAP))
+            button = LCD_BUTTON_SELECT;
+        else
+            button = LCD_BUTTON_NONE;
+        rawTest[value] = button;
+    }
+
+    // Dump the accuracy of different bit truncations.
+    for (bits = 4; bits < 10; ++bits) {
+        int count = 0;
+        for (value = 0; value < 1024; ++value) {
+            value2 = value & (((1 << bits) - 1) << (10 - bits));
+            if (rawTest[value] == rawTest[value2])
+                ++count;
+        }
+        printf("bits = %d, accuracy = %g%%\n", bits, 100.0 * count / 1024.0);
+    }
+    printf("\n");
+
+    // Dump the button mapping table for the selected bit count.
+    bits = 5;
+    printf("static prog_uint8_t const buttonMappings[] PROGMEM = {\n");
+    for (value2 = 0; value2 < (1 << bits); ++value2) {
+        value = value2 << (10 - bits);
+        value3 = value + (1 << (10 - bits)) - 1;
+        button = 0;
+        while (!button && value <= value3) {
+            button = rawTest[value];
+            ++value;
+        }
+        if ((value2 & 0x0F) != 0)
+            printf(", ");
+        else
+            printf("    ");
+        printf("%d", button);
+        if ((value2 & 0x0F) == 0x0F) {
+            if (value2 < ((1 << bits - 1)))
+                printf(",\n");
+            else
+                printf("\n");
+        }
+    }
+    printf("};\n");
+    printf("#define mapButton(value) (pgm_read_byte(&(buttonMappings[(value) >> %d])))\n", 10 - bits);
+
+    return 0;
+}

libraries/FreetronicsLCD/FreetronicsLCD.cpp

@@ -21,18 +21,12 @@
  */
 
 #include "FreetronicsLCD.h"
+#include <avr/pgmspace.h>
 #include <WProgram.h>
 
 #define LCD_BACK_LIGHT          3        // LCD backlight is on D3
 #define LCD_BUTTON_PIN          A0       // Button state is on A0
 
-#define LCD_BUTTON_VALUE_GAP    10
-#define LCD_BUTTON_RIGHT_VALUE  0
-#define LCD_BUTTON_UP_VALUE     145
-#define LCD_BUTTON_DOWN_VALUE   329
-#define LCD_BUTTON_LEFT_VALUE   505
-#define LCD_BUTTON_SELECT_VALUE 741
-
 #define DEBOUNCE_DELAY          10      // Delay in ms to debounce buttons
 
 /**
@@ -261,6 +255,13 @@ void FreetronicsLCD::disableScreenSaver()
  * \sa enableScreenSaver()
  */
 
+// Button mapping table generated by genlookup.c
+static prog_uint8_t const buttonMappings[] PROGMEM = {
+    2, 0, 0, 0, 3, 0, 0, 0, 0, 4, 4, 0, 0, 0, 0, 1,
+    1, 0, 0, 0, 0, 0, 5, 5, 0, 0, 0, 0, 0, 0, 0, 0
+};
+#define mapButton(value) (pgm_read_byte(&(buttonMappings[(value) >> 5])))
+
 /**
  * \brief Gets the next button press, release, or idle event.
  *
@@ -289,24 +290,7 @@ void FreetronicsLCD::disableScreenSaver()
 int FreetronicsLCD::getButton()
 {
     // Read the currently pressed button.
-    int value = analogRead(LCD_BUTTON_PIN);
+    int button = mapButton(analogRead(LCD_BUTTON_PIN));
-    int button;
-    if (value < (LCD_BUTTON_RIGHT_VALUE + LCD_BUTTON_VALUE_GAP))
-        button = LCD_BUTTON_RIGHT;
-    else if (value >= (LCD_BUTTON_UP_VALUE - LCD_BUTTON_VALUE_GAP) &&
-             value <= (LCD_BUTTON_UP_VALUE + LCD_BUTTON_VALUE_GAP))
-        button = LCD_BUTTON_UP;
-    else if (value >= (LCD_BUTTON_DOWN_VALUE - LCD_BUTTON_VALUE_GAP) &&
-             value <= (LCD_BUTTON_DOWN_VALUE + LCD_BUTTON_VALUE_GAP))
-        button = LCD_BUTTON_DOWN;
-    else if (value >= (LCD_BUTTON_LEFT_VALUE - LCD_BUTTON_VALUE_GAP) &&
-             value <= (LCD_BUTTON_LEFT_VALUE + LCD_BUTTON_VALUE_GAP))
-        button = LCD_BUTTON_LEFT;
-    else if (value >= (LCD_BUTTON_SELECT_VALUE - LCD_BUTTON_VALUE_GAP) &&
-             value <= (LCD_BUTTON_SELECT_VALUE + LCD_BUTTON_VALUE_GAP))
-        button = LCD_BUTTON_SELECT;
-    else
-        button = LCD_BUTTON_NONE;
 
     // Debounce the button state.
     unsigned long currentTime = millis();