innomatic

STM32Cube framework provides very similar interface for FatFS as USB MSC we have seen before. Again the same argument applies to this case about the basic unit of read/write operation on a flash memory. In this case, the sector size and the cluster size should be equal to the sector size of flash memory, namely 4KB. This can be set in the file ffconf.h , in which a lot of customization can be done by changing the definitions. In particular, following definitions should be set. In the file user_diskio.c, USER_read and USER_write functions can be implemented as the same way as before. Here we assume that the count is always one for the simplicity. In reality this can be bigger than one if you call f_read() with the buffer size larger than the sector size (4096). However given the limited memory capacity, that is not realistic. By similar token, pdrv variable can be ignored. If ioctl is to be used, then  FatFs allows users to not only read and write files but also to ...

USB Mass Storage Class framework implements bulk-only-transfer (BOT) with SCSI protocol. USB packets from the host eventually converted SCSI transport commands by the middleware, in which data is exchanged (read / write) in the unit of logical block, typically 512 bytes. This SCSI commands works well with SD card system where a dedicated controller does the job of managing the actual memory elements. If you want to use a FLASH chip as a memory unit instead, you need to handle read / write operation directly. Fortunately, most of flash memory support 4KB block erase. This makes the 4096 bytes as a natural choice for the size of the logical block in the file usbd_storage_if.c. In this case, 8Mbit Flash memory was used. During initial enumeration, this information is registered to the host. The middleware maintains one logical block size of buffer and handles USB transaction where each payload is only 64 bytes. It then calls SCSI requests to store / retrieve data to / from physical...