UCPD sink on STM32G4

[RMas]

Is it possible to implement UCPD sink on a stm32G4 without RTOS. What all does that entail? What are the pros and cons?

[FBL]

Hi @RMas 

The following wiki application is based on FreeRTOS STM32StepByStep:Getting started with USB-Power Delivery Sink - stm32mcu and here is the associated example using G4 x-cube-tcpp/Projects/NUCLEO-G474RE/Applications/USB_PD/SNK1M1_Sink at main · STMicroelectronics/x-cube-tcpp (github.com)

Without an RTOS, you would typically have a main loop that continuously polls various functions and manages state transitions manually. 

void USBPD_DPM_Run(void)
{
    // The following code is executed in an infinite loop
    do {
        // Call the Type-C and USB PD stack to handle any CAD (Cable Attachment Detection) events
        (void)USBPD_CAD_Process();

        // Check if the time elapsed since the last Policy Engine (PE) process run is greater than the defined sleep time
        if ((HAL_GetTick() - DPM_Sleep_start[USB_PD_PORT_0]) > DPM_Sleep_time[USB_PD_PORT_0]) {
            // Depending on the role of the device (DRP, Source, or Sink), run the appropriate PE state machine

            USBPD_PE_StateMachine_SNK(USB_PD_PORT_0);

            // Update the start time for the next PE process run
            DPM_Sleep_start[USB_PD_PORT_0] = HAL_GetTick();
        }

        // Execute user-defined code, which could include handling application-specific logic
        USBPD_DPM_UserExecute(NULL);

        // Process any pending USB PD trace data for transmission
        (void)USBPD_TRACE_TX_Process();

    // Continue looping indefinitely
    } while (1u == 1u);
}

Caution: LIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY may need to be adjusted as it may causes the code execution to get stuck in the vPortValidateInterruptPriority function due to overlapping interrupt priorities with kernel operations.

[FBL · Accepted solution]

Hi @RMas 

However, consider that we do not recommend building applications without RTOS in case full compliance with USB PD and Type-C specifications is required. And the code should be 

for (port = 0; port < USBPD_PORT_COUNT; port++)
    {
      if ((HAL_GetTick() - DPM_Sleep_start[port]) >= DPM_Sleep_time[port])
      {
        DPM_Sleep_time[port] =
#ifdef _DRP
          USBPD_PE_StateMachine_DRP(port);
#elif _SRC
          USBPD_PE_StateMachine_SRC(port);
#elif _SNK
          USBPD_PE_StateMachine_SNK(port);
#endif /* _DRP */
        DPM_Sleep_start[port] = HAL_GetTick() + 1;
      }
    }