It finally occurred to me that my 6502 instruction database is unhelpful for writing an emulator: it records that certain instructions can take a variable number of cycles, but not the cause of the variation. As a result, it can't represent things like "an Absolute Indexed With X addressing mode takes an extra cycle for crossing a page boundary, unless the instruction writes a value, unless it reads *and* writes, unless it's INC or DEC". That information would have to be hard-coded into the emulator, and that undermines the values of having a machine-readable reference.

So I'm going to have to expand it to report more detail about the variable cycles, instead of just adding them up.

https://gitlab.com/Screwtapello/isa65xx

WDC sells the W65C02SXB single board computer with a brand new 6502 CPU and a bunch of support chips, at a very reasonable price, for people who want to learn about 6502 programming. Unfortunately, according to the documentation on the website, actually using this thing requires their proprietary Windows IDE to assemble your source code and flash the device.

Is that actually true? Has anyone else bought one of these and developed for it under Linux? I'm hoping for something like "assemble your code, producing something like a ROM image, flash it to the device, hit the reset button, watch the light blink".

https://wdc65xx.com/Single-Board-Computers/w65c02sxb/

The mystery computer from yesterday was… **drumroll**

A Micro-Professor II (1982/83)!

“A what?”

A Micro-Professor II, or MPF-II—made by Multitech, the company that eventually became Acer.

“... Oh?”

Yeah, I’d never heard of it either! There's not much online about it. So it will be interesting to learn about. A few games came with it too, which should be interesting if I can get it going!

https://en.wikipedia.org/wiki/Microprofessor_II

"A curated list of original and reverse-engineered vintage 6502 game sourcecode."

https://github.com/realdmx/retrore

"Second Reality" demo for the #CommanderX16 !
This demo was released at VCF Midwest 2024. It is a re-creation of the famous demo by Future Crew that was originally released at Assembly '93. Only this time, instead of running on a 486 CPU, it is running on a #MOS6502. The music was originally a "Mod-Tracker" type format, but has been reimagined for the Yamaha YM2151 and Vera sound available on the X16.
#retrocomputing #demoscene
https://www.youtube.com/watch?v=_67sF4onNQM

Attempting a rewrite of my 8-bit multi-platform, multi-ISA, assembler's instruction parser. #v80 uses a static tree for mapping instructions into opcodes (2nd image) which is very fast and efficient but hairy to write.

The new approach (1st image), uses an alphabetical list of instructions with a byte to state how many chars of the previous entry are re-used since alphabetically, the left-most chars repeat the most.

There's no guarantee this will even save space (#Z80 ISA is currently 4KB, #MOS6502 is about 1.7KB) and it will likely be slower as more lines will need to be skipped vs. a char-by-char branching approach, but it may help for very large ISAs, the size of which can balloon drastically with lots of shared prefixes, something I'm worried about with adding #eZ80 support. The alternative is adding 'macro' characters for shared-prefixes, but that bloats the native code that needs to be ported between architectures.

I have updated the 6502 Instruction Set Database I made a couple of weeks ago:

https://gitlab.com/Screwtapello/isa65xx

New in this version:

- Now has all the instructions, addressing modes and cycle timings of the 65C02 (the base model, not including extensions added by Rockwell and WDC)
- Represents instructions with the same mnemonic but different behaviour, like the way BIT's immediate mode is different from the others, and indirect JMP is more like an instruction than an addressing mode
- Represents the number of potential extra cycles for each instruction, in addition to the minimum cycle count

As usual, the thing I'm most proud of is the citations and explanations - over 50% of the source file is comments! If you're learning about the 6502 and want something more verifiable than bare assertions on a random website, take a look!