Well, the 6502 in general. It's an extremely important processor in history. People want to emulate NES, Commodore, Atari 8-bit, Apple II - so an accurate 6502 emulator has a HUGE base of nostalgic geeks to improve it.
Yes, and we have freely available, cycle accurate 6502 emulation code bodies along with full coverage tests that include both the official opcodes and many illegal ones. Mostly the ones people used such as LAX, which can get the same value into both registers on a single read.
I just had a fleeting thought right now related to that behavior:
Basically, that opcode works because of how simple the design is. Electrically, wiring both registers up does the trick. And many parts of the chip can work together like that even though none or it was intended.
I wonder what a revisit, that takes these now well understood behaviors
into consideration, would look like!
Zeroing all or multiple registers, same with bit ops, maybe inc, dec...
Many new, efficient instructions are possible. Would be a fun programming exercize and design one too.
Well, the 6502 in general. It's an extremely important processor in history. People want to emulate NES, Commodore, Atari 8-bit, Apple II - so an accurate 6502 emulator has a HUGE base of nostalgic geeks to improve it.