---
title: Debugging STM32 USB Mass Storage Class Device with eMMC
author: peter
date: 2024-06-23 22:25:56 +0800
categories: [Electronics] # Blogging | Electronics | Programming | Mechanical
tags: [electronics, emmc, embedded] # systems | embedded | rf | microwave | electronics | solidworks | automation
# image: assets/img/2024-06-23-Debugging-STM32-USB-/preview.png
---

Summary of my thought process when troubleshooting a board containing eMMC and USB mass storage class device on the STM32L476.

Download Wireshark and the USB pcap plugin.

TLDR: Minimum configuration you should try for troubleshooting is:

- High clock divider (try 4 or 8 or even larger values)
- 1 bit wide MMC bus
- Don't initialize MMC peripheral in the USB MSC initialization function.

## 1. USB connects but then disconnects after a few seconds. The device shows momentarily in the tray, but is not assigned a driver letter.

This also shows in wireshark when the response from the device is a `GET MAX LUN Response[Malformed Packet]` packet.

![wireshark packet capture with malformed packet](/assets/img/2024-06-23-Debugging-STM32-USB-/wireshark.png)

Try return `USBD_OK` for the all functions except `STORAGE_GetMaxLun_FS`. It should show up in explorer with a drive letter and should not disconnect.

This means the functions interacting with the storage device are not working.

---

Make sure you are not re-initializing the MMC peripheral in the `STORAGE_Init_FS` function. This is because in the initialization of the MMC peripheral, `HAL_Delay` is called twice. The use of `HAL_Delay` while the USB device is active appears to cause issues with mounting the device.

<!-- ### 1.1 Try disable eMMC or SD card first

In my board I had eMMC, by commenting out code I isolated the issue to the `SDMMC_PowerState_ON` function which is called during the device initialization. When this code was not called the drive showed up with a drive leter, but when the code was called the drive was not mounted.

```c
(void)SDMMC_PowerState_ON(hmmc->Instance);
```

From this I concluded that any calls to `HAL_Delay` were causing the USB stack to break.

Commenting out the `HAL_Delay` in the `SDMMC_PowerState_ON` function and the one to wait 74 cycles (`HAL_Delay(1U + (74U * 1000U / (sdmmc_clk)))`) caused it to mount properly. I still have to think about what is happening since obviously the delays appear to have good reasons for existing. -->

## 2. "This request is not supported" when formatting drive, files not readable

Try changing the clock division to something larger like `4` or greater. Once it is stable try decreasing the divider to maximize speed. When I used lower values, the bus was unstable and I could not retrieve files or perform format operations.

```c
hmmc1.Init.ClockDiv = 4;
```

## 3. Random files appearing when formatting AND using 4-bit mode

When a drive has already been formatted in 1-bit mode and you try to reformat it, the format fails and there appears to be random files in the apparently formatted drive

The format fails with:

> Windows was unable to complete the format

I guess my board doesn't work in 4-bit mode so I just compromised with 1-bit mode and it worked again.

## 4. DMA not working on STM32L476RET6 STM32L476

Make sure to switch the DMA direction each for RX and TX

Since we are doing bi-directional transfer just use the SDMMC1 DMA request type. Don't use SDMMC1_TX and SDMMC1_RX simulatneously since you need to switch the direction each transfer anyways.

![dma config for sdmmc1](/assets/img/2024-06-23-Debugging-STM32-USB-/dma_settings.png)

Also make sure the preemption priority of the USB is higher than the DMA and SDMMC peripherals and to enable the SDMMC global interrupt.

In my case I am using:

| NVIC interrupt table                                     | Preemption Priority | Sub Priority |
| -------------------------------------------------------- | ------------------- | ------------ |
| SDMMC1 global interrupt                                  | 0                   | 0            |
| DMA2 channel4 global interrupt (Use your DMA controller) | 1                   | 0            |
| USB OTG FS global interrupt                              | 3                   | 0            |

![nvic priority table](/assets/img/2024-06-23-Debugging-STM32-USB-/nvic_settings.png)

## Performance with DMA

Kind of terrible but I am using 1-bit bus width since 4-bit isn't working for me.

![crystaldiskmark performance](/assets/img/2024-06-23-Debugging-STM32-USB-/crystaldiskmark.png)

## Sample code for eMMC and USB mass storage class device

### `main.c`

```c
static void MX_SDMMC1_MMC_Init(void)
{

  /* USER CODE BEGIN SDMMC1_Init 0 */

  /* USER CODE END SDMMC1_Init 0 */

  /* USER CODE BEGIN SDMMC1_Init 1 */

  /* USER CODE END SDMMC1_Init 1 */
  hmmc1.Instance = SDMMC1;
  hmmc1.Init.ClockEdge = SDMMC_CLOCK_EDGE_RISING;
  hmmc1.Init.ClockBypass = SDMMC_CLOCK_BYPASS_DISABLE;
  hmmc1.Init.ClockPowerSave = SDMMC_CLOCK_POWER_SAVE_DISABLE;
  hmmc1.Init.BusWide = SDMMC_BUS_WIDE_1B;
  hmmc1.Init.HardwareFlowControl = SDMMC_HARDWARE_FLOW_CONTROL_DISABLE;
  hmmc1.Init.ClockDiv = 2; // MODIFY THIS AS APPROPRIATE
  if (HAL_MMC_Init(&hmmc1) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_MMC_ConfigWideBusOperation(&hmmc1, SDMMC_BUS_WIDE_1B) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN SDMMC1_Init 2 */
  /* USER CODE END SDMMC1_Init 2 */
}
```

### `usbd_storage_if.c`

```c
int8_t STORAGE_Init_FS(uint8_t lun)
{
  /* USER CODE BEGIN 2 */
  // ALREADY INITIALIZED IN `MX_SDMMC1_MMC_Init` FUNCTION.
  return USBD_OK;
  /* USER CODE END 2 */
}

int8_t STORAGE_GetCapacity_FS(uint8_t lun, uint32_t *block_num, uint16_t *block_size)
{
  /* USER CODE BEGIN 3 */
  HAL_MMC_CardInfoTypeDef card_info;
  HAL_StatusTypeDef status = HAL_MMC_GetCardInfo(&hmmc1, &card_info);
  *block_num = card_info.LogBlockNbr - 1;
  *block_size = card_info.LogBlockSize;
  return status;
  /* USER CODE END 3 */
}

int8_t STORAGE_IsReady_FS(uint8_t lun)
{
  /* USER CODE BEGIN 4 */
  // eMMC IS ALWAYS CONNECTED TO THE BOARD AND IS ALWAYS READY SINCE IT IS
  // INITIALIZED AT THE START.
  return USBD_OK;
  /* USER CODE END 4 */
}

int8_t STORAGE_IsWriteProtected_FS(uint8_t lun)
{
  /* USER CODE BEGIN 5 */
  // ASSUME eMMC IS NEVER WRITE PROTECTED ON THIS PARTICULAR BOARD
  // WRITE PROTECT FEATURE IS NOT USED.
  return USBD_OK;
  /* USER CODE END 5 */
}

int8_t STORAGE_Read_FS(uint8_t lun, uint8_t *buf, uint32_t blk_addr, uint16_t blk_len)
{
  /* USER CODE BEGIN 6 */
  // TODO: USE DMA TRANSFER LATER
  int8_t status = HAL_MMC_ReadBlocks(&hmmc1, buf, blk_addr, (uint32_t)blk_len, TIMEOUT);
  while (HAL_MMC_GetCardState(&hmmc1) != HAL_MMC_CARD_TRANSFER)
    ;
  return status;

  /* USER CODE END 6 */
}

int8_t STORAGE_Write_FS(uint8_t lun, uint8_t *buf, uint32_t blk_addr, uint16_t blk_len)
{
  /* USER CODE BEGIN 7 */
  // TODO: USE DMA TRANSFER LATER
  int8_t status = HAL_MMC_WriteBlocks(&hmmc1, buf, blk_addr, (uint32_t)blk_len, TIMEOUT);
  while (HAL_MMC_GetCardState(&hmmc1) != HAL_MMC_CARD_TRANSFER)
    ;
  return status;
  /* USER CODE END 7 */
}

```

## Sample code DMA version

### `usbd_storage_if.c`

```c
volatile uint8_t mmc_rx_done = 1;
volatile uint8_t mmc_tx_done = 1;

void HAL_MMC_RxCpltCallback(MMC_HandleTypeDef *hmmc)
{
  mmc_rx_done = 1;
}

void HAL_MMC_TxCpltCallback(MMC_HandleTypeDef *hmmc)
{
  mmc_tx_done = 1;
}

// CHANGE DMA DIRECTION
HAL_StatusTypeDef MMC_DMA_direction(uint32_t direction)
{
  HAL_StatusTypeDef status = HAL_OK;
  hdma_sdmmc1.Init.Direction = direction;
  HAL_DMA_Abort(&hdma_sdmmc1);
  HAL_DMA_DeInit(&hdma_sdmmc1);
  return HAL_DMA_Init(&hdma_sdmmc1);
}

//
// [...]
//

/**
 * @brief  Initializes over USB FS IP
 * @param  lun:
 * @retval USBD_OK if all operations are OK else USBD_FAIL
 */
int8_t STORAGE_Init_FS(uint8_t lun)
{
  /* USER CODE BEGIN 2 */
  // ALREADY INITIALIZED IN `MX_SDMMC1_MMC_Init` FUNCTION.
  return USBD_OK;
  /* USER CODE END 2 */
}

/**
 * @brief  .
 * @param  lun: .
 * @param  block_num: .
 * @param  block_size: .
 * @retval USBD_OK if all operations are OK else USBD_FAIL
 */
int8_t STORAGE_GetCapacity_FS(uint8_t lun, uint32_t *block_num, uint16_t *block_size)
{
  /* USER CODE BEGIN 3 */
  HAL_MMC_CardInfoTypeDef card_info;
  HAL_StatusTypeDef status = HAL_MMC_GetCardInfo(&hmmc1, &card_info);
  *block_num = card_info.LogBlockNbr - 1;
  *block_size = card_info.LogBlockSize;
  return status;
  /* USER CODE END 3 */
}

/**
 * @brief  .
 * @param  lun: .
 * @retval USBD_OK if all operations are OK else USBD_FAIL
 */
int8_t STORAGE_IsReady_FS(uint8_t lun)
{
  /* USER CODE BEGIN 4 */
  // if (HAL_MMC_GetState(&hmmc1) == HAL_MMC_STATE_BUSY || HAL_MMC_GetCardState(&hmmc1) != HAL_MMC_CARD_TRANSFER)
  //   return USBD_FAIL;
  return USBD_OK;
  /* USER CODE END 4 */
}

/**
 * @brief  .
 * @param  lun: .
 * @retval USBD_OK if all operations are OK else USBD_FAIL
 */
int8_t STORAGE_IsWriteProtected_FS(uint8_t lun)
{
  /* USER CODE BEGIN 5 */
  // ASSUME eMMC IS NEVER WRITE PROTECTED ON THIS PARTICULAR BOARD
  // WRITE PROTECT FEATURE IS NOT USED.
  return USBD_OK;
  /* USER CODE END 5 */
}

/**
 * @brief  .
 * @param  lun: .
 * @retval USBD_OK if all operations are OK else USBD_FAIL
 */
int8_t STORAGE_Read_FS(uint8_t lun, uint8_t *buf, uint32_t blk_addr, uint16_t blk_len)
{
  /* USER CODE BEGIN 6 */
  mmc_rx_done = 0;
  if (MMC_DMA_direction(DMA_PERIPH_TO_MEMORY) != HAL_OK)
    return USBD_FAIL;
  if (HAL_MMC_ReadBlocks_DMA(&hmmc1, buf, blk_addr, blk_len) != HAL_OK)
    return USBD_FAIL;
  while (!mmc_rx_done)
    ;
  while (HAL_MMC_GetCardState(&hmmc1) != HAL_MMC_CARD_TRANSFER)
    ; // FIXME: IMPLEMENT TIMEOUT FAILSAFE
  return USBD_OK;
  /* USER CODE END 6 */
}

/**
 * @brief  .
 * @param  lun: .
 * @retval USBD_OK if all operations are OK else USBD_FAIL
 */
int8_t STORAGE_Write_FS(uint8_t lun, uint8_t *buf, uint32_t blk_addr, uint16_t blk_len)
{
  /* USER CODE BEGIN 7 */
  mmc_tx_done = 0;
  if (MMC_DMA_direction(DMA_MEMORY_TO_PERIPH) != HAL_OK)
    return USBD_FAIL;
  if (HAL_MMC_WriteBlocks_DMA(&hmmc1, buf, blk_addr, blk_len) != HAL_OK)
    return USBD_FAIL;
  while (!mmc_tx_done)
    ;
  while (HAL_MMC_GetCardState(&hmmc1) != HAL_MMC_CARD_TRANSFER)
    ; // FIXME: IMPLEMENT TIMEOUT FAILSAFE
  return USBD_OK;
  /* USER CODE END 7 */
}

/**
 * @brief  .
 * @param  None
 * @retval .
 */
int8_t STORAGE_GetMaxLun_FS(void)
{
  /* USER CODE BEGIN 8 */
  return STORAGE_LUN_NBR - 1;
  /* USER CODE END 8 */
}
```

## Conclusion

I will update this post with more cases as I run into them. Comment on your experiences debugging USB on STM32 and I'll quote them in the article.