STM32L4R9I-DISCO USB Virtual COM Port - "Unknown Device" Issues

[DerekR]

PCB Silkscreen: MB1311C (No revision number visible)

IDE: Keil uVision 5.16a

FW: STM32Cube_FW_L4_V1.14.0

STM32CubeMX Version: 5.3.0

PC OS: WIndows 7 Ultimate 64-bit

ST VCP Driver Version: 1.5.0

I am experiencing two issues related to this error. If I need to create separate posts for each, please let me know and I apologize in advance. I am new to this processor so bear with me. Let me preface by saying that I have been able to successfully get the VCP functionality working on my devkit, but I am still experiencing intermittent issues.

Issue A. USB low-power must be enabled for USB to work. Why is this? Is this an error with STM32CubeMX?

Steps to reproduce:

1. Open STM32CubeMX and create a project by selecting the STM32L4R9I-DISCO board.
2. It will ask you to initialize all peripherals to default. Select "Yes".
3. Under Pinout & Configuration -> Connectivity -> USB_OTG_FS, set the mode to Device Only. DO NOT enable "Low power" in the "Parameter Settings" tab.
4. Under Pinout & Configuration -> Middleware -> USB_DEVICE, set "Class For FS IP" to "Communications Device Class (Virtual Port Com)".
5. Click the "Project Manager" tab, configure the project with a stack and heap size of 0x1000 for MDK-ARM V5.
6. Generate the code, build and run the project.
7. Plug in the USB cable and wait. You receive "Unknown Device"
8. Now repeat steps 1-6, and be sure to ENABLE "Low power" mode in step 3.
9. Plug in the USB cable. Device is immediately recognized as a virtual COM port device.

After comparing the two projects created in the above steps, I see the following key differences:

I. The "Low power" project sets up the USB interrupt (below), whereas the non-low-power variant doesn't in usbd_conf.c.

/* Peripheral interrupt init */
    HAL_NVIC_SetPriority(OTG_FS_IRQn, 0, 0);
    HAL_NVIC_EnableIRQ(OTG_FS_IRQn);
    if(pcdHandle->Init.low_power_enable == 1)
    {
      /* Enable EXTI Line 17 for USB wakeup */
      __HAL_USB_OTG_FS_WAKEUP_EXTI_ENABLE_IT();
    }

II. OTG_FS_IRQHandler() is declared in stm32l4xx_it.c (below) in the "Low-power" variant while not being declared in the non-low-power variant.

/**
  * @brief This function handles USB OTG FS global interrupt.
  */
void OTG_FS_IRQHandler(void)
{
  /* USER CODE BEGIN OTG_FS_IRQn 0 */
 
  /* USER CODE END OTG_FS_IRQn 0 */
  HAL_PCD_IRQHandler(&hpcd_USB_OTG_FS);
  /* USER CODE BEGIN OTG_FS_IRQn 1 */
 
  /* USER CODE END OTG_FS_IRQn 1 */
}

Any thoughts, comments, or feedback on this? Again I am new to USB on the STM32, so this might be a silly question :).

Issue B. Unplugging and plugging the USB cable into the PC multiple (5-10) times eventually results in "Unknown Device" within Device Manager.

Steps to reproduce:

1. Create a "Low-power" USB project using STM32CubeMX as mentioned above in step 8.
2. Load and run the code on the devkit and wait for the PC to properly recognize the virtual COM port.
3. Unplug the USB cable and wait for the device to disappear from device manager.
4. Plug the USB cable back into the PC and wait for it to be properly recognized as a virtual COM port.
5. Repeat steps 3 and 4 ten times. During this time, the device will stop being recognized and will appear as an "Unknown Device". Unplugging and re-plugging the USB cable does not resolve the problem and the firmware appears to have locked up.

Thoughts, comments, or feedback?

Thanks for any help or insight received!

Derek