Reverse Engineering the PROM for the SGI O2
Since the early 2000s, the potential for upgrading the CPU in the Silicon Graphics O2 with a 900 MHz RM7900 has been blocked by the inability to modify the PROM firmware. To that end, I built ip32prom-decompiler, a program that decompiles the PROM into sources that can be reassembled into a bit-identical image. The decompiler goes to great lengths to produce assembly that is understandable and modifiable by replacing known constants, recognizing and replacing memory addresses with labels, inserting comments and function descriptions, marking function bounds, and many other niceties. In this article I'll describe the process of reverse engineering the structure and contents of the PROM so that I could build the decompiler.
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