This is the beginnings of an RS232 based bootloader for PIC32MX devices, intended to be used with my HobbyOS project.

The Bootloader FSM looks like this:

This command will return a version code.
Send: 'V'
Response: 4 byte version

This command will return an error code corresponding to the application verificaiton failure, if any.
Send: 'R' Response: 8 character string (not null terminated).

This command will erase a page of memory starting at the address passed.
Send: 'E' + 4 byte address
Response: 'e' when erase is complete if a valid address, 'f' otherwise

This command will program a row starting at the address specified.
Send: 'P' + 4 byte address
Response: 'p'
Then, send 512 bytes + 4 byte CRC32
Response: 'q' if the CRC failed, 'r' otherwise

This command will stop communication, and attempt to boot the applicaiton.
Send: 'B'
Response: 'b'

If a 500 ms timeout occurs while waiting for data, a 't' will be sent.
If a command is not recognized, a '?' will be sent.