Posted on March 10, 2018 at 08:38
The follow code snippet is generated in sd_diskio.c by CubeMX (4.0) when using FreeRTOS (STM32Cube_FW_F7_V1.9.0):
/**
* @brief Gets Disk Status
* @param lun : not used
* @retval DSTATUS: Operation status
*/
DSTATUS SD_status(BYTE lun)
{
return SD_CheckStatus(lun);
}
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and SD_status is passed to FatFs as the disk_status function. Internally FatFs uses a semaphore to prevent reentrant filesystem API calls to the same drive, but the disk_status function is called BEFORE the lock is acquired. As a result, when FatFs is used with FreeRTOS with the SD card as the disk subsystem, the SD_status function may easily be called by one task while another task is the middle of a FatFs API call and actively performing a disk operation.
The upshot is that SD_status must be reentrant, but calls to the SD_CheckStatus functionhave to beserialized and so SD_status may wrongly return STA_NOINIT because an I/O operation is in progress. In other words, it's fine that SD disk operation is in progress; the disk_status function just wants to know if the SD card is 'ok'.
The workaround is to modify SD_status in the preceding user block as follows:
// Workaround for non-thread-safe version of SD_status implemented below.
// FatFs calls SD_status (via disk_status if ff.c) BEFORE it locks the
// file pointer. As a result, SD_status must be reentrant. For our purposes,
// FatFs only checks for STA_NOINIT and this cannot change after successful
// initialization unless the media is removed.
// See: https://community.st.com/external-link.jspa?url=http%3A%2F%2Felm-chan.org%2Ffsw%2Fff%2Fdoc%2Fdstat.html
DSTATUS SD_status(BYTE lun)
{
return Stat;
}
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#define SD_status SD_status_not_thread_safe
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