The disk_read function reads sector(s) from the storage device.
DRESULT disk_read ( BYTE pdrv, /* [IN] Physical drive number */ BYTE* buff, /* [OUT] Pointer to the read data buffer */ DWORD sector, /* [IN] Start sector number */ UINT count /* [IN] Number of sectros to read */ );
The memory address specified by buff is not that always aligned to word boundary because the type of argument is defined as BYTE*. The misaligned read/write request can occure at direct transfer. If the bus architecture, especially DMA controller, does not allow misaligned memory access, it should be solved in this function. There are some workarounds described below to avoid this issue.
Generally, a multiple sector transfer request must not be split into single sector transactions to the storage device, or you will not get good read throughput.