Thanks for the great tips! Ill be going over these in detail and make the recommended changes. Exactly the review I was looking for, thanks guys!

Ill be working on porting this to the supercpu for the C64 and C128. Very impressive work!

Hey folks, Im working on a clone of the Atari 2600 pacman (the one everyone hated, but was the most selling game for the console). Why? Well, why not. And the 128 doesnt have a lot of native games for it.

Anyway, I wanted to share the code and see if anyone had any thoughts on improving it ...

If any Commodore 128 users (or VICE) would like to see what Im working on:

https://github.com/Commodore64128/ataripac128

Movement is still a bit wrong.. its taking me some time to figure things out.

Correct. Subtracting an 8 bit number from a 16.

Looking at your examples, i think i see my issue. Im putzing around with the carry flag, doing a SEC before the SBC, etc. Seems your code works without worrying about the carry.

Im still scratching my head though trying to understand why subtracting ...

Hey guys, this is likely a noob question, but Ive seen some other 16 bit subtractions that dont seem to take into account a rollover. What I mean is:

C000: 01 FF


If I subtract $05, and the carry is set, then i know I can DEC $C001. But if its zero, I cant. So my subtraction code is no good, since ...

Hey folks, Ive mashed up a few things and have come up with an emulated 65816 computer with 16MB of ram, running on bare metal raspberry pi 4 or 400. Im working on a ROM as well, and was thinking to use BDD's monitor.

Anyway, if anyone is interested in playing with this, i can put the code up on gi ...

Of the top of head, so untested I'm afraid - but I think you can do it in a pretty small loop without temporary storage:

loop:
lsr
beq done
bcc loop
eor #1
jmp loop
done:

The result is in the carry flag, it will be set if the number of bits was odd, and clear if it was even.


That's ...

hey folks. In working through this emulator, I ran into the P bit in the 8086 processor flag register. This one is a 1 if there are an even number of bits on after a calculation. A zero is there if its odd.

Here's an implementation I put together. Im not keen on the number of cycles it will take ...

Thanks for all the responses.

MicroCoreLabs - I sent you a PM. Very interested in your work there. I neeeeed a pcjr board for sure. And Id like to see a 65816 replacement as well, if it could somehow mirror ram as the supercpu does.

Im working on a simple 8086 emulator for the 65816 (supercpu on the c64/128). right now, the opcodes are just a bunch of statements such as:

jsr fetch_op
cmp #$xx
beq doXX
cmp #$xy
beq doXY
...
...

I dont care for this. For one, im pretty sure im going to have problems with the short branches. and ...

Its a little confusing...

The SCPU has its own RAM on board (and you can add up to 16mb).

Bank $00, $01, $f8-$ff are found in all SuperCPUs, with or without expansion RAM. Bank $00 and $01 are built-in static RAM, and banks $F8-$FF are used by or reserved for system ROM (SuperCPU ROM, not c64 ROM ...

a question for OP. docs say:

What determines when parameters are passed on the stack vs registers?

The safest is to look at the generated code. What it does is to scan the parameter list left to right and bind registers in a given order. First it uses the CPU register(s) for a single parameter ...

Please consider at least running a github if only for your example code and updated binaries so that we can post issues. Since this appears to be the only place to talk with you and provide feedback, I have no choice but to post a long message.

Im creating a c64 target (for the supercpu), but ...

a question for OP. docs say:


18.3 Calling convention
The calling convention is fairly complex in all its details, but for most common situations it is reasonable
simple.
If parameters are passed on the stack the caller is responsible for doing any cleanup. The called function can
use any ...