Originally posted by dentman42
@TDB: So the 2500a has a backup copy of 2100 firmware? Or does this safe mode just get it running enough to accept a flash and to report itself to the system as a 2100, but not enough to actually read or write discs?
The 2x00 series drives are all basically the same, they have a 1MB Flash ROM, and the binary upload is a large portion of that. In the front portion of the ROM is a boot loader that has an extremely small command subset. Enough to report what it is and flash the drive and that's about it. The boot loader checks the integrity of the primary firmware and executes that if the checksum is correct, otherwise it drops into safe mode. The only problem occurs if you checksum a firmware which crashes before it gets to the command processing subroutine, or crashes within it. If this happens you have a brick, software can't get it back, perhaps there is a JTAG port or test points for incircuit programming.
Checking the boot loader the name it reports is
_NEC DVD+RW ND-2100A 0.06 03091600
The front of the ROM also includes calibration data, serial numbers, product identification (2500 vs 2100) and regioning information.
The DOS flasher was written by analysing the boot loader.