Post Reply 
Peculiarities in HP supplied S/SX and G/GX ROM dumps
03-26-2019, 05:32 PM (This post was last modified: 07-28-2020 09:56 AM by Giuseppe Donnini.)
Post: #3
RE: Peculiarities in HP supplied S/SX and G/GX ROM dumps
You're absolutely right! Some time ago, when I wrote my own HP-48 decompiler/disassembler to study the ROM (especially the hidden parts of it), I stumbled over the same problem. At first, I believed I had found 64 nibbles of hidden ROM underneath the MMIO device. After all, the region below the bankswitcher (#7F000h-#7FFFFh) is not entirely empty either, so it was not completely unreasonable to think this was genuine ROM code. But soon enough I found out that I was wrong in my assumption and I ended up patching zeros over the area #00100h - #0013Fh to avoid getting strange results while disassembling in the vicinity of that region.

I could never make sense of it, but I think you came up with a clever explanation. At least there can be little doubt that the nibbles stem from an actual MMIO chip, because, if I remember correctly, the suspicious successions of 3's exactly correspond to the default positions of write-only hardware registers.
Find all posts by this user
Quote this message in a reply
Post Reply 


Messages In This Thread
RE: Peculiarities in HP supplied S/SX and G/GX ROM dumps - Giuseppe Donnini - 03-26-2019 05:32 PM



User(s) browsing this thread: 1 Guest(s)