STM32H743 USB Host MSC + FATFS f_opendir() Deadlock Issue in Bootloader

Hello Everyone,

I am working on a custom USB bootloader project on STM32H743 using:

• USB Host MSC
• FATFS
• External QSPI Flash
• Internal Flash update
• IAR Workbench
• HAL drivers

My bootloader detects USB pendrive successfully and I can see:

• Appli_state == APPLICATION_READY
• f_mount() returns FR_OK

But the system gets stuck / deadlocked when calling:

DIR dir;

if(f_opendir(&dir, "0:/") != FR_OK)
{
 return UPDATE_NONE;
}

The MCU hangs inside f_opendir() and never returns.

Current flow:

MX_USB_HOST_Init();

while(1)
{
 MX_USB_HOST_Process();

 if(Appli_state == APPLICATION_READY)
 {
 HAL_Delay(500);

 update_flags = ver_check();

 break;
 }
}

Inside ver_check():

if(f_mount(&USB_FatFs, USBHPath, 0) != FR_OK)
{
 return UPDATE_NONE;
}

if(f_opendir(&dir, USBHPath) != FR_OK)
{
 return UPDATE_NONE;
}

Additional Information:

• USB Host MSC works until f_opendir()
• No FreeRTOS used
• USB drive detected properly
• f_mount() succeeds
• Deadlock occurs specifically at f_opendir()
• Tried both "0:/" and USBHPath
• Tried adding delays after APPLICATION_READY

    Has anyone faced f_opendir() blocking forever on H7?

Any guidance would be greatly appreciated.

Thank you.