STM32 USB CDC some data lost with Win 10

Question

I use USB device - STMicroelectronics development board. Use firmware, that support usb hardware. Its works as USB serial port.

On host PC (win10 21H1) i use serial terminal ("Tera Term") for get data from my device. I use standart windows usbserial driver.

My device sending data. If data flow is small (1-2-5 kByte/s) - all work fine. But if i speed up (flow about 100 kByte/s or more) - i see data loss.

I communicated with STMicroelectronics support. We checked issue. We saw USB communication with USB analyzer. We think, than it's windows side problem.

Also, I use a custom port read utility. Data integrity problem persists.

In received data i saw lost 64 or 128... multiple of 64 bytes. 64bytes - endpoint size in my case. See linked data for more information.

I create USB_test project in CubeMx. And add simple code for sending data to PC. Loop data sending if previous CDC transmit complete. Adding delays is unacceptable: firstly, it is not 100% elimination of losses; secondly, it has a bad effect on the bandwidth of the channel.

//in main() function 

uint8_t is_transmit = 0;

HAL_Delay(5000);
uint8_t Buf[2048];
uint8_t k = 48;
// fill the array with printable characters
for(uint16_t i=0; i<sizeof(Buf)-2; i++){
    if(k > 100) {
        k = 48;
    }
    Buf[i] = k++;
}
// array - is a one string line
Buf[sizeof(Buf)-2] = '\r';
Buf[sizeof(Buf)-1] = '\n';
        
    
while (1)
{
    if(is_transmit == 0){
        is_transmit = 1;
        //HAL_Delay(1); // add delay on 1 ms reduces the likelihood of losses by an order of magnitude
        CDC_Transmit_FS(Buf, sizeof(Buf));
    }
}

In CDC_TransmitCplt_FS() i flash is_transmit.

static int8_t CDC_TransmitCplt_FS(uint8_t *Buf, uint32_t *Len, uint8_t epnum)
{
    ---
    extern uint8_t is_transmit;
    is_transmit = 0;
    ---

  return result;
}

Information from ST support communication and USB analyzer log file. https://drive.google.com/drive/folders/1CvTPfaFGmcFxD4V5zTvsVE6U26DNwG2v?usp=sharing

How i fix this issue? I need data flow from device to host 500 kB/s or more.

Best regards, Andrey.

Answer 1

According to https://wiki.segger.com/CDC, there is a bug in Windows 10 that causes loss of some data packets over CDC-ACM. Nowadays, I am able to reproduce the issue with full-speed USB device and Windows 10 Pro (22H2). I can see (via an external USB analyzer) the missing data were successfully transferred to WIN10.