Posted on August 08, 2013 at 18:04For it to work the routines you substitute will need to have equivalent function. The READ will be relatively easy, and something you should test/validate outside the USB MSC first.
WRITE will be more problematic to emulate on the NAND because you will need to read the original NAND erasable unit, erase the NAND, insert the blocks you need to update/change, then write the whole new unit to the NAND. This is a technique often referred to as deblocking.
The blocks the MSC works on are likely 512 bytes (sector), the minimum erase unit/block on the NAND is likely 128 Kbytes, your code will need to deal with this disparity, and perhaps cache and lazy-write blocks back to the NAND so you don't destroy it with unnecessary erase/write cycles. ie the MSC gets 256 single block writes to different locations within the same NAND erase unit.
The MSC interface is also going to want to know/report the capacity of the NAND device.
A search of the SD functions and structures used should be illustrative of what the MSC interface requires.
