Baseband Bootrom Protocol

This is the protocol used to talk to the old, and probably the new baseband, at the bootrom level. The old bootrom didn't have a sig checking, the new one does.

Protocol

AT
0x30
2 byte length
n byte data
2 byte checksum
sends A5 on success, 5A on failure

3G

On the iPhone 3G bootrom, the "protocol" section is pretty much identical, besides the last line, which is instead this:

sends 01 on success, FF on failure

Implementations

bootrom.h in gbootloader

The modem chipset that provides cellular capabilities to a device

The first significant code that runs on an iOS device

The bootloader on iOS devices and some later iPods, or a general name for the pre-kernel boot process