Updated Master MOS versions

[tom_seddon]

I've put together some updated versions of the Master MOS, with bug fixes, and code rearrangement to simplify MegaROM setup. For more info about the changes, and download links, see here: https://github.com/tom-seddon/acorn_mos ... refresh.md

Getting this working will involve some DIY! The releases include a 16 KB MOS ROM and an associated 16 KB utils ROM for bank 15, but putting together a full ROM image is up to you (as is actually getting it working in your Master). And it's also highly experimental, which is a polite way of saying that there will almost certainly be bugs. Hopefully not bad ones, but I make no promises. But, ukwebb, james and I have been using it our Masters, and nothing awful has happened yet...

Ongoing goals for this project:

1. fix any obvious MOS bugs: crash, hang, behaviour not matching documentation, stuff fixed in a later version, that sort of thing
2. improve performance where possible
3. retain compatibility with existing MOS versions

Ongoing non-goals for this project:

1. add new stuff

Goal 3 and non-goal 1 are related. I figure the MOS is well designed enough that the sideways ROM mechanism offers enough options here, so I've got no plans to add new APIs, or change the existing ones, or add any new features. (If I'm feeling particularly bold, I might backport something from a newer Acorn version to an older one. MOS 3.20 could do with built-in SRAM utils, for example, and MOS 5.11i has a couple of tweaks that it wouldn't hurt to include.)

Any feedback welcome. And I'll post in this thread when I release further versions of this.

--Tom

P.S. this is an offshoot of my Master MOS disassembly project: https://www.stardot.org.uk/forums/viewtopic.php?t=27904