STM32L4 USBD CDC-MSC Combination Device Class CDCtransmit-FS() Sending Issue

1350280419 · ‎2024-03-11

The STM32USB library calls the function CDC TransmitFS, which can only be sent in the CDC ReceiveFS loop and data in the main. The cdc ->TxState flag has always been 1, so only the USBD_cDC SetTxBuffer was successfully called. However, the USBD_cDC TransmitPacket, USBD_cDC DataIn, and subsequent CDC TransmitCplt cannot be called.

There are two solutions to watching the forum: 1. Place it in an interrupt with the same priority as USB and call CDC TransmitFS to send it. Only the call succeeds 2. 'Call this function EP0_RxReady before sending. But both methods can cause the program to freeze.

Both CDC_Receive_FS and CDC_Transmit_FS are implemented in usbd_cdc_if. c. Calling CDC_Receive_FS in CDC_Receive_FS can send and receive messages in a normal loopback.

The following is the implementation of two functions：

FBL · ‎2024-03-12

Hello @1350280419

Would you please share your project to reproduce the issue? Which L4 board are you using?

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1350280419 · ‎2024-03-12

Thanks,I am developing STM32L4R7VIT6 on my circuit board.How can I deliver this whole project to you.

Now, I am using USBD_LL_Transmit() instead of CDC_Transmit_FS() to send messages,it works.

I'm not sure if there are any issues with directly using the lower sending function, but the fact is that it can work normally.