Bug STM32F405 USB HOST CDC

[vekli]

STM32CubeMX v6.5.0 

STM32Cube FW_F4 V1.27.0

USB_FS HOST CDC

usbh_cdc.h

function static void CDC_ProcessReception(USBH_HandleTypeDef *phost)

line 767

 if (((CDC_Handle->RxDataLength - length) > 0U) && (length > CDC_Handle->DataItf.InEpSize))

fix:

 if (((CDC_Handle->RxDataLength - length) > 0U) && (CDC_Handle->RxDataLength > CDC_Handle->DataItf.InEpSize))

[Pavel A.]

This is this line:

https://github.com/STMicroelectronics/stm32_mw_usb_host/blob/e9cbb348511bda0e04cf1ce586534a96212903e4/Class/CDC/Src/usbh_cdc.c#L754

or https://github.com/STMicroelectronics/STM32CubeF4/blob/3d6be4bd406f275728e0a321cc371c62a3100533/Middlewares/ST/STM32_USB_Host_Library/Class/CDC/Src/usbh_cdc.c#L754

Can you explain a bit more, please, why there is a bug?

[vekli]

Yes. You are right line 754.

Error because length = USBH_LL_GetLastXferSize(phost, CDC_Handle->DataItf.InPipe);

and then we compare length > CDC_Handle->DataItf.InEpSize It never happens because max length is InEpSize, readings stops after first read, if you run USBH_CDC_Receive with buffer size bigger then max endpoint packet size then it will read only first packet and then reading will be stopped..

I guess that comparison needed for analyze how many bytes left for read CDC_Handle->RxDataLength

Becasue USB wok on packet basis we will continue reading if number of left bytes bigger then maximum packet size in other case we should stop reading.

[Pavel A.]

Ah, I see. length is the last received size, and it cannot be > endpoint size.

But it can be less than the EP size, this means a short packet or ZLP, which ends the transfer.

So probably should be:

 if (((CDC_Handle->RxDataLength - length) > 0U) && (length == CDC_Handle->DataItf.InEpSize))
{
  //continue receiving
}
else
{
   // end transfer
}

@Hana Slimi​  what do you think?

[vekli]

I just shared my experience. In my project bug fixed with if (((CDC_Handle->RxDataLength - length) > 0U) && (CDC_Handle->RxDataLength > CDC_Handle->DataItf.InEpSize))

If you will use length == CDC_Handle->DataItf.InEpSize then you will continue reading even if requested length == InEpSize but reading should be stopped it that case.

[KDJEM.1]

Hello @vekli​,

I reported this issue internally. 

I will get back to you with more details as soon as possible.

Thank you for your contribution.

Internal ticket number: 137249 (This is an internal tracking number and is not accessible or usable by customers).

Kaouthar