STM32H745XIHX entering bootloader in code: Switch USB from VCP to DFU on User Input

[ilikeCODINGbutitdoesntlikeME]

Hi all,

I am a newer STM32 programmer, and I have been working on the STM32H745 Discovery board for the last few months. Something that I would like to do is be able to switch into USB DFU Mode within a UI that I have made for this board. I took inspiration from this post and changed the address to the appropriate one for the STM32H745. I would like to prerequisite that the USB port is initially configured as a VCP/CDC device. Here is the code that I have:

void (*SysMemBootJump) (void);

void USB_BootloaderInit()
{
	volatile uint32_t addr = 0x1FFF9800;	//from AN2606

	__disable_irq();

	// Reset USB OTG_FS

	// Disable caches
	SCB_DisableICache();
	SCB_DisableDCache();

	// Remap vector table
	HAL_RCC_DeInit();		//Reset the system clock
	SysTick->CTRL = 0;		//Reset the  SysTick Timer
	SysTick->LOAD = 0;
	SysTick->VAL  = 0;
	SysMemBootJump = (void (*)(void)) (*((uint32_t *)(addr + 4)));	//Point the PC to the System Memory reset vector
	__set_MSP(*(uint32_t *)addr);	//Set the Main Stack Pointer

	SysMemBootJump();				//Run our virtual function defined above that sets the PC

	while(1);
}

 Now, to test this code, I am simply calling it at the very beginning of main as such:

int main(void)
{

  /* USER CODE BEGIN 1 */
USB_BootloaderInit();


  /* USER CODE END 1 */
/* USER CODE BEGIN Boot_Mode_Sequence_0 */
  int32_t timeout;
/* USER CODE END Boot_Mode_Sequence_0 */

  /* MPU Configuration--------------------------------------------------------*/
  MPU_Config();

/* USER CODE BEGIN Boot_Mode_Sequence_1 */
  /* Wait until CPU2 boots and enters in stop mode or timeout*/
  timeout = 0xFFFF;
  while((__HAL_RCC_GET_FLAG(RCC_FLAG_D2CKRDY) != RESET) && (timeout-- > 0));
  if ( timeout < 0 )
  {
  Error_Handler();
  }

But, when I get on STM32Cube Programmer, I do not see the device. I have tried using the debugger, but I think I am running into different issues because of the dual core nature of this. I would get errors from random things. The one that particularly stumped me is this line:
SysMemBootJump = (void (*)(void)) (*((uint32_t *)(addr + 4))); //Point the PC to the System Memory reset vector

would consistently trigger a hard fault error (IMPRECISSER)

I have looked around the forum posts that exist and I do not think I have found something quite like my issue.

Thank you for your time!

[FBL · Accepted solution]

Hi @ilikeCODINGbutitdoesntlikeME 

DFU and CDC are different USB protocols. You need to implement a composite device for your application to switch to DFU mode.

Here is an article on how to implement the USB device composite class USB DFU + HID. You can follow the same principle to implement your CDC application.

[ilikeCODINGbutitdoesntlikeME]

I've determined it has something to do with the stuff being initialized on startup, so I ended up just having a check flag that is written in a RAM section that does not get overwritten. Then, on reset, the assembly code forces the STM32H745 into the bootloader. This has been a very repeatable way to do this, although I am unsure if CubeIDE/CubeMX overwrite this file yet.

Thank you all for your help!