STM32+SDIO+FreeRTOS+FATFS在带有DMA和CACHE的平台的调试注意要点

1.前言

此前在没有FreeRTOS操作系统上实现了在STM32H7平台上，连接SD卡，使用DMA传输并使得D-Cache保持回写模式下正常工作时的笔记如下：

STM32+SDIO+FATFS在带有DMA和CACHE的平台的调试注意要点_Fairchild_1947的博客-CSDN博客

此次加入FreeRTOS实时操作系统，并同样实现上述功能。

2.注意事项

        加入FreeRTOS实时操作系统的情况硬件设置同没有操作系统的硬件设置。不过在设置操作系统可使用的堆栈时最好设置的大一些，因为操作系统版本的sd_diskio.h文件中，使用队列进行进程间通信。此处由于STM32H7的内部SRAM非常大，且笔者比较喜欢使用操作系统的内存申请，所以直接给操作系统分配了256KB，内存分配算法选择默认的heap_4即可，这个算法是最优的。

​

        生成代码后，与没有操作系统一样，需要添加使用Cache的宏定义

        然而就在编译之后，若使用C99标准编译会发生报错，因为C99标准定义的变量作用范围是顶定义前的一对括号结束，但是在SD_read方法中，源码在else中没有定义ret，所以需要在else情况添加ret变量的定义。编译即可通过。

具体位置请看如下代码，重要位置已经用中文注释写出：

DRESULT SD_read(BYTE lun, BYTE *buff, DWORD sector, UINT count)
{
  DRESULT res = RES_ERROR;
  uint32_t timer;
#if (osCMSIS < 0x20000U)
  osEvent event;
#else
  uint16_t event;
  osStatus_t status;
#endif
#if (ENABLE_SD_DMA_CACHE_MAINTENANCE == 1)
  uint32_t alignedAddr;
#endif
  /*
  * ensure the SDCard is ready for a new operation
  */

  if (SD_CheckStatusWithTimeout(SD_TIMEOUT) < 0)
  {
    return res;
  }

#if defined(ENABLE_SCRATCH_BUFFER)
  if (!((uint32_t)buff & 0x1F))
  {
#endif
    /* Fast path cause destination buffer is correctly aligned */


    //这里是ret第一次定义的位置，作用范围仅在此if条件成立的区域中
    uint8_t ret = BSP_SD_ReadBlocks_DMA((uint32_t*)buff, (uint32_t)(sector), count);
    

    if (ret == MSD_OK) {
#if (osCMSIS < 0x20000U)
    /* wait for a message from the queue or a timeout */
    event = osMessageGet(SDQueueID, SD_TIMEOUT);

    if (event.status == osEventMessage)
    {
      if (event.value.v == READ_CPLT_MSG)
      {
        timer = osKernelSysTick();
        /* block until SDIO IP is ready or a timeout occur */
        while(osKernelSysTick() - timer <SD_TIMEOUT)
#else
          status = osMessageQueueGet(SDQueueID, (void *)&event, NULL, SD_TIMEOUT);
          if ((status == osOK) && (event == READ_CPLT_MSG))
          {
            timer = osKernelGetTickCount();
            /* block until SDIO IP is ready or a timeout occur */
            while(osKernelGetTickCount() - timer <SD_TIMEOUT)
#endif
            {
              if (BSP_SD_GetCardState() == SD_TRANSFER_OK)
              {
                res = RES_OK;
#if (ENABLE_SD_DMA_CACHE_MAINTENANCE == 1)
                /*
                the SCB_InvalidateDCache_by_Addr() requires a 32-Byte aligned address,
                adjust the address and the D-Cache size to invalidate accordingly.
                */
                alignedAddr = (uint32_t)buff & ~0x1F;
                SCB_InvalidateDCache_by_Addr((uint32_t*)alignedAddr, count*BLOCKSIZE + ((uint32_t)buff - alignedAddr));
#endif
                break;
              }
            }
#if (osCMSIS < 0x20000U)
          }
        }
#else
      }
#endif
    }

#if defined(ENABLE_SCRATCH_BUFFER)
    }
    else
    {
      /* Slow path, fetch each sector a part and memcpy to destination buffer */
      int i;

    //需要在这里添加一个对ret的定义
	uint8_t ret;

      for (i = 0; i < count; i++)
      {
        ret = BSP_SD_ReadBlocks_DMA((uint32_t*)scratch, (uint32_t)sector++, 1);
        if (ret == MSD_OK )
        {
          /* wait until the read is successful or a timeout occurs */
#if (osCMSIS < 0x20000U)
          /* wait for a message from the queue or a timeout */
          event = osMessageGet(SDQueueID, SD_TIMEOUT);

          if (event.status == osEventMessage)
          {
            if (event.value.v == READ_CPLT_MSG)
            {
              timer = osKernelSysTick();
              /* block until SDIO IP is ready or a timeout occur */
              while(osKernelSysTick() - timer <SD_TIMEOUT)
#else
                status = osMessageQueueGet(SDQueueID, (void *)&event, NULL, SD_TIMEOUT);
              if ((status == osOK) && (event == READ_CPLT_MSG))
              {
                timer = osKernelGetTickCount();
                /* block until SDIO IP is ready or a timeout occur */
                ret = MSD_ERROR;
                while(osKernelGetTickCount() - timer < SD_TIMEOUT)
#endif
                {
                  ret = BSP_SD_GetCardState();

                  if (ret == MSD_OK)
                  {
                    break;
                  }
                }

                if (ret != MSD_OK)
                {
                  break;
                }
#if (osCMSIS < 0x20000U)
              }
            }
#else
          }
#endif
#if (ENABLE_SD_DMA_CACHE_MAINTENANCE == 1)
          /*
          *
          * invalidate the scratch buffer before the next read to get the actual data instead of the cached one
          */
          SCB_InvalidateDCache_by_Addr((uint32_t*)scratch, BLOCKSIZE);
#endif
          memcpy(buff, scratch, BLOCKSIZE);
          buff += BLOCKSIZE;
        }
        else
        {
          break;
        }
      }

      if ((i == count) && (ret == MSD_OK ))
        res = RES_OK;
    }
#endif
  return res;
}

3.测试结果

        测试结果同没有操作系统的时候。