STM32U595 bootloader resets when no peripheral is connected

[christophe.durand]

Here is my main and jump to bootloader :

int main(void)
{
    HAL_Init();
    SystemPower_Config();
    SystemClock_Config();

    HAL_Delay(500); // Catch bootloader constantly resetting

    jump_to_bootloader();
    while (1)
    {
        HAL_Delay(50);
    }
}

#define BOOTLOADER_ADDR			(0x0BF90000UL)

HAL_StatusTypeDef jump_to_bootloader(void)
{
	__disable_irq();

	HAL_RCC_DeInit(); // Must be run before disabling systick because it depends on it
	HAL_DeInit();

	SysTick->CTRL = 0U; // Disable systick
	SysTick->LOAD = 0U;
    SysTick->VAL  = 0U;

	int count = sizeof(NVIC->ICER)/sizeof(NVIC->ICER[0]);
	for (int i = 0; i < count; i++)
	{	// Clear pending interrupts
		NVIC->ICER[i]=0xFFFFFFFFUL;
		NVIC->ICPR[i]=0xFFFFFFFFUL;
	}

	void (*jump_to_bootloader_fptr)(void);
	jump_to_bootloader_fptr = (void (*)(void)) (*((uint32_t *) ((BOOTLOADER_ADDR + 4))));

	__enable_irq();

	__set_MSP(*(uint32_t *)BOOTLOADER_ADDR);
	jump_to_bootloader_fptr();

	return HAL_ERROR; // Should never get there because of jump
}

 

When manually debugging using gdb, when breaking at jump_to_bootloader_fptr(); , I use step instruction to step into the code, I can see that the addresses of instructions being executed are in the bootloader’s address range.

Here’s some gdb debugging output :

Breakpoint 3, jump_to_bootloader () at /home/src/bsp/bsp_bootloader.c:53
53		jump_to_bootloader_fptr();
(gdb) si
0x08000636	53		jump_to_bootloader_fptr();
(gdb) si
0x0bf98c38 in ?? ()
(gdb) 
0x0bf98c3a in ?? ()
(gdb) 
0x0bf98a10 in ?? ()
(gdb) 
0x0bf98a12 in ?? ()

I can execute ‘stepi’ (step instructions) for a long time and it will stay in the bootloader’s address range. 

But when I execute 'continue' command, the program restarts at the user code's address range.

0x0bf90cf6 in ?? ()
(gdb) 
0x0bf90cee in ?? ()
(gdb) c
Continuing.

Breakpoint 1, main () at /home/src/main.c:36
36	    HAL_Init();

So it means that the bootloader resets after some condition is met. However, reading Figure 125 of AN2606, the bootloader should be 'stuck' in a loop of checking for peripheral detection and should not reset.

My option bytes : TZEN=0, nSWBOOT0=0 nBOOT0=1

So my question : is it expected that the bootloader resets when no peripheral is connected, or is there something wrong with my setup ?