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Jump-to-user-code.md

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Jump-to-user-code

stm32 Custom Bootloaders always requires you this little peice of code snippet for jumping from your bootloader code to the application code.

BOOTLOADER CODE

WHAT CODE DOES?

1.pointing the function pointer to the reset handler of the user application.

	uint32_t reset_handler_add = *((volatile uint32_t *) (FLASH_SECTOR2_BASE_ADDRESS+4)); 
	void (*app_reset_handler)(void) = (void*) reset_handler_add;

2.Disable RCC, set it to default (after reset) settings Internal clock, no PLL, etc

	HAL_RCC_DeInit();
	HAL_DeInit();

3.Disabling Systick timer and loading it with the default values.

	SysTick->CTRL = 0x0;
	SysTick->LOAD=0;
	SysTick->VAL=0;
  1. Remapping the vector table offset

SCB->VTOR = FLASH_SECTOR2_BASE_ADDRESS;

  1. Setting the MSP value and calling the reset handler of the the user-application.
	uint32_t msp_value = *((volatile uint32_t *)FLASH_SECTOR2_BASE_ADDRESS);
	__set_MSP(msp_value);
	app_reset_handler();

#define FLASH_SECTOR2_BASE_ADDRESS 0x08008000

void jump_to_user_app1(void)
{
    
	uint32_t reset_handler_add = *((volatile uint32_t *) (FLASH_SECTOR2_BASE_ADDRESS+4)); 
	void (*app_reset_handler)(void) = (void*) reset_handler_add;
	HAL_RCC_DeInit();
	HAL_DeInit();
	SysTick->CTRL = 0x0;
	SysTick->LOAD=0;
	SysTick->VAL=0;
	SCB->VTOR = FLASH_SECTOR2_BASE_ADDRESS;
	uint32_t msp_value = *((volatile uint32_t *)FLASH_SECTOR2_BASE_ADDRESS);
	__set_MSP(msp_value);
	app_reset_handler();
	
}

USER-APPLICATION CODE

  1. Change the Vector Table base offset field in the system_stm32f4xx.c file with the first 2 bytes of the new flash sector.

#define VECT_TAB_OFFSET 0x8000

  1. Change the origin address flash memory in the linker script of your user-application priject.

FLASH (rx) : ORIGIN = 0x08008000, LENGTH = 512K

This snippet is for STM32's M0+ families, It worked 🎉 fine for me on stm32f411.

I will update the code for other family aswell.