10 years, 3 months ago.

<<quote>>but to add support for FAT16 on an SPI Flash chip is...<</quote>> Extremely easy :D

Well maybe not extremely, but it is definately doable. When that is done it should be doable to port the program which uses an SD card to your SPI flash. First a question though: Sure you don't want to use an SD card?

Strangely I can't seem to find examples where it is done. I have done something close myself once, since I don't want to spend too much time searching, lets use that example: http://mbed.org/users/Sissors/code/S25FL216K_USBFileSystem/. Instead of USBFileSystem you get FATFileSystem (http://mbed.org/teams/mbed-official/code/FATFileSystem/). You need to implement the following functions in your library:

    virtual int disk_initialize() { return 0; }
    virtual int disk_status() { return 0; }
    virtual int disk_read(uint8_t * buffer, uint64_t sector, uint8_t count) = 0;
    virtual int disk_write(const uint8_t * buffer, uint64_t sector, uint8_t count) = 0;
    virtual int disk_sync() { return 0; }
    virtual uint64_t disk_sectors() = 0;

Most are straightforward, stuff like disk_sync is from another era and you can just ignore it. The read, write and numbder of sectors you have to implement, the others you may implement. Done that? Well now you are finished, you have a FATFileSystem running on your flash chip.

One little detail which is irritating: The default sector size for a FATFileSystem is 512B. I believe you can change the sector size that FATFileSystem uses, but that you would need to look up yourself. In the linked example IIRC the minimum erase size of the flash IC was 4kB, and in the end I just did the easy solution (since it is mainly a proof of concept for the USBFileSystem lib), and only used 512B of each 4kB sector. But that is of course not very area efficient. If you find a flash IC with a minimum erase size of 512B you are set, otherwise you either need to work around the issue (for example copying data to RAM), or you need to get the file system lib to use different sector size, or you need to accept that you don't use your entire memory.