STM32 Enter DFU from VCP

[McNickel]

Hello,

I have an application where I would like to switch the STM32G431KB into the built-in bootloader (using USB DFU) by sending a specific byte through the CDC Virtual COM port. I was able to get the unit into DFU mode by running the "USB_BootloaderInit" function below when a button is pressed, however when I try running the function upon reception of data from the CDC port, Windows either does not see the device or gives me a "Device Descriptor Request Failed" notification.

I get the feeling the USB port is still doing some work or there are interrupts still running, but I am not sure how to go about checking what is going on or properly clearing any pending interrupts, or what exactly is going on and I wanted to see if anyone could help point me in the right direction.

This is the function that allows me to enter into the bootloader:

void USB_BootloaderInit()
{
	volatile uint32_t addr = 0x1FFF0000;
	SysMemBootJump = (void (*)(void)) (*((uint32_t *)(addr + 4)));	//Point the PC to the System Memory reset vector
 
	HAL_RCC_DeInit();		//Reset the system clock
	SysTick->CTRL = 0;		//Reset the SysTick Timer
	SysTick->LOAD = 0;
	SysTick->VAL = 0;
 
	__set_MSP(*(uint32_t *)addr);
 
	SysMemBootJump();
 
	while(1);
}

It is being called when the correct character is received through the CDC_Receive_FS function as part of the CubeIDE USB Device Middleware.

Currently, I have tried running the USBD_DeInit and USBD_Stop functions before the USB_BootloaderInit function, along with putting some delay (5ms - 1Second using timers) between the DeInit/Stop and BootloaderInit functions, with no avail.

Any help is appreciated

[Uwe Bonnes]

You need to set VTOR an SYSCFG MEMMODE. But better is to have a switch in early startup code to check for some magicnumber in RAM that you set just before reset when DFU is requested.

[McNickel]

Thank you Uwe Bonnes,

I had been thinking about putting a statement in early startup, but I wasn't sure how to go about it so I was avoiding it, but it worked flawlessly.

For anyone who is reading this in the future, here is what I did:

When the correct character is received on the serial port, I run the following function:

void USB_TriggerBootloader()
{
	SYSCFG->MEMRMP &= 0xFFFFFFF9;		//Remap the memory (may not be necessary)
	SYSCFG->MEMRMP |= 1;
	switchToBootloader = 0x11;			//Set the noinit variable to be read by startup code
	NVIC_SystemReset();					//Reset the system
}

the switchToBootloader variable is defined as:

uint8_t switchToBootloader __attribute__ ((section (".noinit")));

The ".noinit" prevents the variable from being re-initialized upon a reset.

After a reset, the first lines of code in the main function are an if statement which checks switchToBootloader and, if it is equal to 0x11, runs the following function:

void (*SysMemBootJump) (void);
 
void USB_BootloaderInit()
{
	switchToBootloader = 0x00;	//Reset the variable to prevent being stuck in the bootloader (since a device reset wont change it)
	volatile uint32_t addr = 0x1FFF0000;	//The STM32G431KB system memory start address
	SysMemBootJump = (void (*)(void)) (*((uint32_t *)(addr + 4)));	//Point the PC to the System Memory reset vector
 
	HAL_RCC_DeInit();		//Reset the system clock
	SysTick->CTRL = 0;		//Reset the SysTick Timer
	SysTick->LOAD = 0;
	SysTick->VAL = 0;
 
	__set_MSP(*(uint32_t *)addr);	//Set the Main Stack Pointer
 
	SysMemBootJump();				//Run our virtual function defined above that sets the PC
 
	while(1);
}

And it works reliably!

EDIT: I added the declaration for SysMemBootJump.

[Davorin]

How did you define SysMemBootJump?

Otherwise gives me:

error: called object 'SysMemBootJump' is not a function or function pointer

 Update: Never mind...fund it (o;

[TDK]

You can reset the USB peripheral using code similar to:

 // disable USB
 __HAL_RCC_USB_OTG_FS_CLK_ENABLE();
 __HAL_RCC_OTGFS_FORCE_RESET();
 __HAL_RCC_OTGFS_RELEASE_RESET();