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https://github.com/taigrr/arduinolibs
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Save the RNG seed to flash memory on the Due
This commit is contained in:
Rhys Weatherley
parent
c0470980de
commit
2e64f4bec9
@ -153,13 +153,13 @@ Because the device may be restarted before the first hour expires, there
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is a special case in the code: the first time that the entropy pool
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fills up, a save will be automatically forced.
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\note The Arduino Due does not have EEPROM so it cannot save the random
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number seed across system restarts. Instead the \link RNGClass RNG\endlink
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class will mix in data from the CPU's built-in True Random Number
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Generator (TRNG). Assuming that the CPU's TRNG is trustworthy,
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this should be sufficient to properly seed the random number generator.
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It is recommended to also mix in data from other noise sources just in
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case the CPU's TRNG is not trustworthy.
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The Arduino Due does not have EEPROM so RNG saves the seed into
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the last page of system flash memory instead. The RNG class will also
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mix in data from the CPU's built-in True Random Number Generator (TRNG).
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Assuming that the CPU's TRNG is trustworthy, this should be sufficient
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to properly seed the random number generator. It is recommended to
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also mix in data from other noise sources just in case the CPU's TRNG
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is not trustworthy.
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To use the random number generator properly, there are some regular tasks
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that must be performed every time around the application's main loop().
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@ -28,10 +28,10 @@
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#include <Arduino.h>
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#if defined (__arm__) && defined (__SAM3X8E__)
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// The Arduino Due does not have any EEPROM natively on the main chip.
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// However, it does have a TRNG so seed saving is not as critical.
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#define RNG_NO_EEPROM 1
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#define RNG_DUE_TRNG 1
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// However, it does have a TRNG and flash memory.
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#define RNG_DUE_TRNG 1
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#else
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#define RNG_EEPROM 1
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#include <avr/eeprom.h>
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#endif
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#include <string.h>
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@ -113,9 +113,9 @@
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* conditions programmatically, then it may make sense to force a save()
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* of the seed upon shutdown.
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*
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* \note The Arduino Due does not have EEPROM so it cannot save the random
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* number seed across system restarts. Instead the RNG class will mix
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* in data from the CPU's built-in True Random Number Generator (TRNG).
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* The Arduino Due does not have EEPROM so RNG saves the seed into
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* the last page of system flash memory instead. The RNG class will also
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* mix in data from the CPU's built-in True Random Number Generator (TRNG).
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* Assuming that the CPU's TRNG is trustworthy, this should be sufficient
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* to properly seed the random number generator. It is recommended to
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* also mix in data from other noise sources just in case the CPU's TRNG
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@ -205,6 +205,31 @@ RNGClass::~RNGClass()
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#if defined(RNG_DUE_TRNG)
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// Find the flash memory of interest. Allow for the possibility
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// of other SAM-based Arduino variants in the future.
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#if defined(IFLASH1_ADDR)
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#define RNG_FLASH_ADDR IFLASH1_ADDR
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#define RNG_FLASH_SIZE IFLASH1_SIZE
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#define RNG_FLASH_PAGE_SIZE IFLASH1_PAGE_SIZE
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#define RNG_EFC EFC1
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#elif defined(IFLASH0_ADDR)
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#define RNG_FLASH_ADDR IFLASH0_ADDR
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#define RNG_FLASH_SIZE IFLASH0_SIZE
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#define RNG_FLASH_PAGE_SIZE IFLASH0_PAGE_SIZE
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#define RNG_EFC EFC0
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#else
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#define RNG_FLASH_ADDR IFLASH_ADDR
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#define RNG_FLASH_SIZE IFLASH_SIZE
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#define RNG_FLASH_PAGE_SIZE IFLASH_PAGE_SIZE
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#define RNG_EFC EFC
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#endif
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// Address of the flash page to use for saving the seed on the Due.
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// All SAM variants have a page size of 256 bytes or greater so there is
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// plenty of room for the 48 byte seed in the last page of flash memory.
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#define RNG_SEED_ADDR (RNG_FLASH_ADDR + RNG_FLASH_SIZE - RNG_FLASH_PAGE_SIZE)
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#define RNG_SEED_PAGE ((RNG_FLASH_SIZE / RNG_FLASH_PAGE_SIZE) - 1)
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// Stir in the unique identifier for the Arduino Due's CPU.
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// This function must be in RAM because programs running out of
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// flash memory are not allowed to access the unique identifier.
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@ -215,25 +240,38 @@ static void stirUniqueIdentifier(void)
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uint32_t id[4];
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// Start Read Unique Identifier.
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EFC1->EEFC_FCR = (0x5A << 24) | EFC_FCMD_STUI;
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while ((EFC1->EEFC_FSR & EEFC_FSR_FRDY) != 0)
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RNG_EFC->EEFC_FCR = (0x5A << 24) | EFC_FCMD_STUI;
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while ((RNG_EFC->EEFC_FSR & EEFC_FSR_FRDY) != 0)
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; // do nothing until FRDY falls.
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// Read the identifier.
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id[0] = *((const uint32_t *)IFLASH1_ADDR);
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id[1] = *((const uint32_t *)(IFLASH1_ADDR + 4));
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id[2] = *((const uint32_t *)(IFLASH1_ADDR + 8));
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id[3] = *((const uint32_t *)(IFLASH1_ADDR + 12));
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id[0] = *((const uint32_t *)RNG_FLASH_ADDR);
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id[1] = *((const uint32_t *)(RNG_FLASH_ADDR + 4));
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id[2] = *((const uint32_t *)(RNG_FLASH_ADDR + 8));
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id[3] = *((const uint32_t *)(RNG_FLASH_ADDR + 12));
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// Stop Read Unique Identifier.
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EFC1->EEFC_FCR = (0x5A << 24) | EFC_FCMD_SPUI;
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while ((EFC1->EEFC_FSR & EEFC_FSR_FRDY) == 0)
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RNG_EFC->EEFC_FCR = (0x5A << 24) | EFC_FCMD_SPUI;
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while ((RNG_EFC->EEFC_FSR & EEFC_FSR_FRDY) == 0)
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; // do nothing until FRDY rises.
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// Stir the unique identifier into the entropy pool.
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RNG.stir((uint8_t *)id, sizeof(id));
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}
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// Erases the flash page containing the seed and then writes the new seed.
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// It is assumed the seed has already been loaded into the latch registers.
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__attribute__((section(".ramfunc")))
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static void eraseAndWriteSeed()
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{
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// Execute the "Erase and Write Page" command.
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RNG_EFC->EEFC_FCR = (0x5A << 24) | (RNG_SEED_PAGE << 8) | EFC_FCMD_EWP;
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// Wait for the FRDY bit to be raised.
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while ((RNG_EFC->EEFC_FSR & EEFC_FSR_FRDY) == 0)
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; // do nothing until FRDY rises.
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}
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#endif
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/**
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@ -250,6 +288,9 @@ static void stirUniqueIdentifier(void)
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* This function should be followed by calls to addNoiseSource() to
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* register the application's noise sources.
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*
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* The \a eepromAddress is ignored on the Arduino Due. The seed is instead
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* stored in the last page of system flash memory.
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*
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* \sa addNoiseSource(), stir(), save()
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*/
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void RNGClass::begin(const char *tag, int eepromAddress)
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@ -260,7 +301,7 @@ void RNGClass::begin(const char *tag, int eepromAddress)
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// Initialize the ChaCha20 input block from the saved seed.
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memcpy_P(block, tagRNG, sizeof(tagRNG));
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memcpy_P(block + 4, initRNG, sizeof(initRNG));
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#if !defined(RNG_NO_EEPROM)
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#if defined(RNG_EEPROM)
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if (eeprom_read_byte((const uint8_t *)address) == 'S') {
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// We have a saved seed: XOR it with the initialization block.
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for (int posn = 0; posn < 12; ++posn) {
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@ -269,9 +310,17 @@ void RNGClass::begin(const char *tag, int eepromAddress)
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}
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}
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#elif defined(RNG_DUE_TRNG)
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// The Arduino Due does not have EEPROM so we instead XOR the
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// initialization block with some output from the CPU's TRNG.
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// Do we have a seed saved in the last page of flash memory on the Due?
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int posn, counter;
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if (((const uint32_t *)RNG_SEED_ADDR)[0] == 'S') {
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// XOR the saved seed with the initialization block.
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for (posn = 0; posn < 12; ++posn)
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block[posn + 4] ^= ((const uint32_t *)RNG_SEED_ADDR)[posn + 1];
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}
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// If the device has just been reprogrammed, there will be no saved seed.
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// XOR the initialization block with some output from the CPU's TRNG
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// to permute the state in a first boot situation after reprogramming.
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pmc_enable_periph_clk(ID_TRNG);
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REG_TRNG_CR = TRNG_CR_KEY(0x524E47) | TRNG_CR_ENABLE;
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REG_TRNG_IDR = TRNG_IDR_DATRDY; // Disable interrupts - we will poll.
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@ -559,11 +608,19 @@ void RNGClass::save()
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{
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// Generate random data from the current state and save
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// that as the seed. Then force a rekey.
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#if !defined(RNG_NO_EEPROM)
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++(block[12]);
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ChaCha::hashCore(stream, block, RNG_ROUNDS);
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#if defined(RNG_EEPROM)
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eeprom_write_block(stream, (void *)(address + 1), 48);
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eeprom_update_byte((uint8_t *)address, 'S');
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#elif defined(RNG_DUE_TRNG)
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unsigned posn;
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((uint32_t *)(RNG_SEED_ADDR))[0] = 'S';
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for (posn = 0; posn < 12; ++posn)
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((uint32_t *)(RNG_SEED_ADDR))[posn + 1] = stream[posn];
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for (posn = 13; posn < (RNG_FLASH_PAGE_SIZE / 4); ++posn)
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((uint32_t *)(RNG_SEED_ADDR))[posn + 13] = 0xFFFFFFFF;
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eraseAndWriteSeed();
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#endif
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rekey();
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timer = millis();
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@ -642,9 +699,13 @@ void RNGClass::destroy()
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{
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clean(block);
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clean(stream);
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#if !defined(RNG_NO_EEPROM)
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#if defined(RNG_EEPROM)
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for (int posn = 0; posn < SEED_SIZE; ++posn)
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eeprom_write_byte((uint8_t *)(address + posn), 0xFF);
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#elif defined(RNG_DUE_TRNG)
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for (unsigned posn = 0; posn < (RNG_FLASH_PAGE_SIZE / 4); ++posn)
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((uint32_t *)(RNG_SEED_ADDR))[posn] = 0xFFFFFFFF;
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eraseAndWriteSeed();
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#endif
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}
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