So I hacked on cc65 instead, making some large, obvious improvements. (Note: the maintainer of cc65 did not accept them).

Can you elaborate on what they did and why they were not accepted?


* Static parameter passing (enabled with --static-params): uses fixed memory locations for parameter ...

A straightforward approach would be to treat the 6502 like a 16-bit RISC with a large, uniform register file, implemented as zero page memory. This allows a standard register allocator to be used. Ideally, the register allocation would be global (i.e. whole program) to make best use of the ...

It's possible to use garbage collection with C, although it's a hack. Basically the garbage collector looks for anything that might be a pointer to allocated memory, although it has no way of knowing that it actually is a pointer, so you get some false positives. More dangerously, if a pointer is ...

In all honesty, though, implementing LAS won't offer a significant time advantage to XBA/LDA, since the 6502 has only a single bus inside it.

You don't have to physically move data from one register to another; you can just rename the accumulator. That's why I used the word "toggle", because I ...

Thankfully, what you illustrated above is not toggling, but rather is clearly a "data stack" in the Forth processor parlance. You have, simply, a 2-deep stack.

There's no difference between an exchange of A and B, followed by LDA, and a transfer from A to B, followed by LDA.

However, this, too ...

I was thinking it might be good if LDA toggled between A and B. As in:

lda #1 ; A = 1, B = ?
lda #2 ; A = 2, B = 1
lda #3 ; A = 3, B = 2

The advantage is that you don't need an LDB instruction.

For VBR's original question - what small delta would you make to 65c02 - I'd start with the '816's B accumulator, and then I'd take some other goodies from the '816. I'd prefer separate opcodes for 16-bit operations, if there were any. I don't much like the modes.

A "B" register isn't a bad idea ...

Some other random instruction ideas:

sti #imm, zp
sti #imm, abs
cmpeq #imm, rel8
cmpne #imm, rel8
add #imm (without carry)
sub #imm (without borrow)
lda (ind), #
sta (ind), #
push zp
push abs
push #

Also the HuC6280 has swap instructions, useful or not?

sax
say
sxy

----------------------

What ...

Regarding "memory is super cheap now"...when it was a struggle to fit a CPU on a chip, it might have made sense to waste memory in exchange for a simpler CPU. But when the entire system, including memory, is on a single chip, it makes no sense to waste memory, since memory is the biggest cost.

Look ...

What are the simplest, most useful improvements you could make, taking the WDC65C02 as a base?

1) 24-bit program counter

This would allow 16MB of ROM code without bank switching. RAM, I/O, and ROM data would be located in the lower 64K.

jsr/jmp/rts/rti redefined for 24-bit operation.

New opcodes ...

The Terminator (1984 model)

Bravo. Well done.

Do you know what other famous robot has the same 'brain'?

I'll be back later to check your answer.

What's the exciting project? There's no shortage of C/C++ 6502 emulators...

Are you writing a linker also or just going straight to executable?

Just what the world needs, another 6502 assembler.

I'm not trying to spoil your fun, but there are so many already, it's hard to believe that none are suitable. Did you try ca65, for example?