I’m using the STM32L476 discovery kit to test an application where a battery-powered product powers up a USB memory stick, connects to it, writes some data, and then shuts the stick down again, removing power. I've used the STM32 Cube to generate the code and I have the application largely working, data writes fine when I am single-stepping in the debugger, however, if I let it free-run it looks like the power to the stick is being removed prematurely, as the file system on the USB memory stick is being corrupted. Is there a correct way to check if all transfers have been completed on the USB and the stick is idle, before stopping USB? I am using USBH_MSC_IsReady, but it seems to not be sufficient.
For now, simply adding a 1 second delay before USBH_Stop seems to solve the problem, however, this isn't ideal in a product, and I have no idea if this is long enough.
Code below
void writeToStick(void)
{
uint32_t i;
uint8_t success = TRUE;
/* Init host Library, add supported class and start the library. */
MX_USB_HOST_Init();
while (USBH_MSC_IsReady(&hUsbHostFS) == 0)
{
MX_USB_HOST_Process();
}
//initialise FAT file system
MX_FATFS_Init();
MX_USB_HOST_Process();
fileError = f_mount(&USBHFatFS, (TCHAR const*)USBHPath, 0);
MX_USB_HOST_Process();
fileError = f_open(&MyFile, "STM32.TXT", FA_CREATE_ALWAYS | FA_WRITE);
if (fileError == FR_OK)
{
//write our 100-byte buffer until we have 1 Mb of data
for (i=0; i < (1024*10); i++)
{
if(f_write(&MyFile, wtext, sizeof(wtext)-1, (void *)&wbytes) != FR_OK)
{
success = FALSE;
}
}
//an f_ close should do an f_sync as well, flushing file buffers
f_close(&MyFile);
//wait for USB buffers to flush
while (USBH_MSC_IsReady(&hUsbHostFS) == 0)
{
MX_USB_HOST_Process();
}
}
//unmount file system
fileError = f_mount(NULL, (TCHAR const*)USBHPath, 1);
MX_USB_HOST_Process();
//wait again, in case some more buffers need flushing
while (USBH_MSC_IsReady(&hUsbHostFS) == 0)
{
MX_USB_HOST_Process();
}
//unlink driver
MX_FATFS_DeInit();
MX_USB_HOST_Process();
//and wait again, just in case
while (USBH_MSC_IsReady(&hUsbHostFS) == 0)
{
MX_USB_HOST_Process();
}
//stop the USB, and remove power
USBH_Stop(&hUsbHostFS);
/* De-Init */
USBH_DeInit(&hUsbHostFS);
}
