Forcing bootloader startup through program

[tolis81]

Hello,
I am trying to find out if it is possible to trigger programmatically the double-tap on reset button function, implemented in modified version of Atmel's SAM-BA bootloader. In case this is not possible using the stock board setup, if this can be achieved by hardware or bootloader modifications.

[MartinL]

Hi tolis81,

Here's some code that will programmatically place the board into bootloader mode after a system reset:

Code: [Select]

// Code to programmatically initiate bootloader mode after reset
#define BOOT_DOUBLE_TAP_ADDRESS           (0x20007FFCul)
#define BOOT_DOUBLE_TAP_DATA              (*((volatile uint32_t *) BOOT_DOUBLE_TAP_ADDRESS))
#define DOUBLE_TAP_MAGIC 0x07738135

void setup()
{
  pinMode(LED_BUILTIN, OUTPUT);               // Initialise the LED as an OUTPUT
}

void loop()
{
  for (uint8_t i = 0; i < 5; i++)             // Blink the built-in LED for 5 seconds before reset
  {
    digitalWrite(LED_BUILTIN, HIGH);          // Turn LED on
    delay(500);                               // Wait half a second
    digitalWrite(LED_BUILTIN, LOW);           // turn the LED off by making the voltage LOW
    delay(500);                               // Wait for a second
  }
  BOOT_DOUBLE_TAP_DATA = DOUBLE_TAP_MAGIC;    // Start in bootloader mode after reset
  NVIC_SystemReset();                         // Reset the microcontroller
}

[qniens]

For (Adafruit) SAMD51 devices (Feather M4, ItsyBitsy M4, etc) the 'magic' code is:

Code: [Select]

#define DOUBLE_TAP_MAGIC 0xf01669efUL
#define BOOT_DOUBLE_TAP_ADDRESS     (HSRAM_ADDR + HSRAM_SIZE - 4)

unsigned long *a = (unsigned long *)BOOT_DOUBLE_TAP_ADDRESS;
*a = DOUBLE_TAP_MAGIC;
NVIC_SystemReset();

[MartinL]

Hi qniens,

Thanks, good to know that the magic works on the SAMD51 as well.

MartinL

[tolis81]

Hi MartinL and qniens. Thank you both for the answers. Hopefully I'll get my board this week for testing. The post delays are awful.

tolis81