8085 undocumented instructions are missing

[RetroAND]

Intel microprocessor has two undocumented flags in their documentation and a series of instructions both to work with those flags, 16 bit operations and even a software interrupt. All 8085 have those instructions even if they weren't documented by the designers. As GHidra follows the original Intel documentation the instruction set is incomplete.

I would have implemented the missing parts, however my skills with sleigh is null. For this reason I would like to ask if more experienced GHidra developers would help having this part completed.

Personally I use GHidra to help documenting old computer systems and unfortunately I found a system that uses this set of undocumented instructions. If someone could help, it would be greatly appreciated.

Thanks in advance

[GhidorahRex]

Can you provide any documentation on the instructions?

[RetroAND]

Of course. The instructions were tested across batches and found to be working on all them. They were present in memos etc. but nobody knows why Intel decided to keep them a secret.

UnDoc85.pdf
Undoc_8085.pdf

The mnemonics used for this small set of instructions is the one from the second document (JNK, RSTV, etc.) but left the other for reference.

[hjanetzek]

This case is also discussed here #2299 with some preliminary you could try @RetroAND
1577081

For a thorough analysis how these flags are implemented:
http://www.righto.com/2013/02/looking-at-silicon-to-understanding.html

[RetroAND]

Hello @hjanetzek ,

The truth is while I would want to do it myself I don't have neither the knowledge in Sleight nor the time to implement the routines. I am designing spare parts for the machine whose code I'm studying and this plus the hardware reverse engineering take up my entire time. Sorry if that's a disapointment, but I'm constrained at this point.

In any case thanks for your intervention.

[hjanetzek]

Hi @RetroAND, no problem :) Just wanted to add some pointers - I'm a hobbyist reverse-engineer myself, specializing on mid-80s home organs.
In case you considered to use MAME for development (it has quite a lot RC2014 parts implemented and is generally a great reference to understand (old) hardware) I've started work on a plugin to link MAME debugger with Ghidra - without this tool some things would have been impossible for me to figure out https://github.com/orgs/mamedev/discussions/54#discussioncomment-8573209

I'll probably get back to a 8085 device soon and then could try to bring the undocumented instruction code into shape for a PR.