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Graduate
December 21, 2025
Question

USB-PD attention callback never get's triggered?

  • December 21, 2025
  • 2 replies
  • 63 views

Problem 

When i call 

* USBPD_PE_SVDM_RequestAttention

I get a OK message response but the callback never gets called.  

* USBPD_VDM_SendAttention

 

Curious to know if there's any good way to debug this? 

 

Current debugging steps

I have a STM32G0-Disco board setup to capture the messages over USB-PD and display them with ST's USB-PD monitoring software.  So i know the attention pin is not currently activating.  I have a breakpoint to make sure that USBPD_PE_SVDM_RequestAttention is being called.  If i wait a few seconds and then trigger it to call USBPD_PE_SVDM_RequestAttention again i get a BUSY error.  So i figure it's trying to send it, it just can't?

 

 

My project

I'm using this as my base with a stm32G071- nucleo board.  I grab the CC lines from usb with a breakout board that passes the USB datalines through.  

https://github.com/STMicroelectronics/STM32CubeG0/tree/master/Projects/STM32G081B-EVAL/Applications/USB-PD/USB-PD_Consumer_1port

And i'm migrating all the USB-PD calls that relate to Display Port/VDM  over from this project

https://github.com/STMicroelectronics/STM32CubeG0/tree/master/Projects/STM32G081B-EVAL/Demonstrations/DemoUCPD

 

PD captures

 

Current2.png

 

Current capture.png

 

 

 

Screenshot 2025-12-21 at 10.12.14 AM.png

Screenshot 2025-12-21 at 10.01.39 AM.png

    This topic has been closed for replies.

    2 replies

    Technical Moderator
    December 24, 2025

    Hello @Brenden_PLUS 

    Thank you for your feedback!

    Would you check if the callbacks are properly implemented as in G0 demo?

    Graduate
    December 26, 2025

    So i call the function USBPD_PE_SVDM_RequestAttention.

     

    But it never fires the callback USBPD_VDM_SendAttention.  

    https://github.com/STMicroelectronics/STM32CubeG0/blob/24d13255ffa4eca73d133561a3df72f7df90d302/Projects/STM32G0C1E-EV/Demonstrations/Modules/ucpd/usbpd_vdm_user.c#L550

     

     

    I thank you for your support, but i'll be on vacation till January 15.  @FBL you been a huge help for me to figure out USB PD with the stm32.  

     

    Technical Moderator
    December 30, 2025

    Thank you @Brenden_PLUS  It 's a pleasure to support you ! Enjoy your vacation.

    Attention message can only be sent after a successful USB PD explicit contract and after entering the DisplayPort Alternate Mode. When HPD pin is low, and mode is not entered, the stack may silently ignore or queue the Attention message without sending. 

    I found also according to USB Type-C™ and Power Delivery DisplayPort Alternate Mode, section 4.6, an Attention message with IRQ set to 1 marks the end of USB PD DP Alternate Mode communication and the
    beginning of standard DP operation, when all the DP signals are mapped to the Type-C connections.

    An internal ticket 224463 is submitted to dedicated team for any insights into internal precompiled library management of USBPD_PE_SVDM_RequestAttention.