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A
akorsich
Associate
April 25, 2025
Solved

STM32F4 USBX CDC-ACM Bulk IN endpoint Stall

  • April 25, 2025
  • 1 reply
  • 554 views

I am looking for help solving a CDC-ACM problem with Azure Rtos ThreadX, and the USBX Middleware for STM32F4.

My device is an STM32F427VGTx.

I currently have a project that uses the USBX host library. I am connecting up to 4x CDC-ACM devices through an off-the-shelf USB Hub.

I had problems connecting multiple devices through the hub, but I have solved that after following the solution to update the USBX core bsp from the stm32-mw-usbx repo. (STM32H7 and USB2514 Continued Problems)

 

I can connect to all 4x CDC-ACM devices (data class instance and control class instance enumerate successfully on all devices).

I can send commands to all devices using the control interface by sending a transfer request to the control endpoint.

I can read from up to two CDC-ACM devices, but the third and fourth device will timeout after calling ux_host_class_cdc_acm_read. The function returns a transfer-request-timeout after failing to retrieve the ux_host_semaphore. The status of ux_host_semaphore_get is always TX_NO_INSTANCE and is set by tx_semaphore_cleanup() after semaphore timeout in a thread.

I am calling ux_host_class_cdc_acm_read inside a thread. It works for up to two devices. The first two still work while the third and fourth don't.

Best answer by akorsich

I have resolved the problem by reducing the amount of endpoints used in each CDC-ACM device.

 

For anyone struggling with a similar problem, count how many endpoints you are using.

The STM32 USB Peripheral has up to 8 endpoints. After reducing to two endpoints each (BULK IN, CMD OUT) I am able to succesfully connect and communicate with 4 CDC-ACM devices.

Our CDC-ACM devices was built using STM32G4 and the initial example used 4 endpoints (BULK IN, BULK OUT, CMD OUT, ISOCHRONOUS). That was why I could only connect to two devices before.

 

Thank you @FBL for the advice.

1 reply

F
FBL
Technical Moderator
May 7, 2025

Hi @akorsich 

Are you interfacing low speed devices? You may need to check this limitation section 2.14.2 Host packet transmission may hang when connecting through a hub to a low-speed device.

To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.Best regards,FBL
A
akorsichAuthorAnswer
Associate
May 7, 2025

I have resolved the problem by reducing the amount of endpoints used in each CDC-ACM device.

 

For anyone struggling with a similar problem, count how many endpoints you are using.

The STM32 USB Peripheral has up to 8 endpoints. After reducing to two endpoints each (BULK IN, CMD OUT) I am able to succesfully connect and communicate with 4 CDC-ACM devices.

Our CDC-ACM devices was built using STM32G4 and the initial example used 4 endpoints (BULK IN, BULK OUT, CMD OUT, ISOCHRONOUS). That was why I could only connect to two devices before.

 

Thank you @FBL for the advice.

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