Page 1 of 6
Gameboy on 32X
Posted: Wed Jan 21, 2009 10:37 am
by mic_
Here's something I've been tinkering with a bit lately:
It's dog slow right now, because the code is all plain C that hasn't been optimized or tweaked for the 32X. There's also some weird bug that seems to corrupt the ROM if I add a .gb file larger than 128kB (this doesn't happen with the PC version).
Posted: Wed Jan 21, 2009 11:19 am
by ob1
Hey ! Looks interesting.
;)
Any way to look into your sources ?
Posted: Wed Jan 21, 2009 11:47 am
by mic_
Perhaps after I've cleaned it up a bit and fixed some bugs. Right now it's quite useless.
Posted: Wed Jan 21, 2009 2:06 pm
by TmEE co.(TM)
wow, this is awesome Ö
Posted: Wed Jan 21, 2009 6:57 pm
by AamirM
Dude, that is just so cool and awesome!!
Posted: Wed Jan 21, 2009 9:05 pm
by Jorge Nuno
W00t!
Doesn't the gameboy have the Z80 as a CPU? maybe it could be ran "almost" natively on the megadrive.
Posted: Wed Jan 21, 2009 9:12 pm
by Shiru
Jorge Nuno wrote:Doesn't the gameboy have the Z80 as a CPU?
Not, it has it's own unique CPU, something between 8080 and Z80, partially compatible.
Posted: Wed Jan 21, 2009 9:16 pm
by Jorge Nuno
Well what if the 68k supervises the code for z80 unknown instructions and handle them, while it feeds the z80 with pure code. I don't know if it is possible to do that fast enough, doing the address translation at the same time.
Posted: Thu Jan 22, 2009 5:17 pm
by mic_
I've looked at the SH2 assembly that gcc generates (I'm compiling with -O2) for my emulator, and it's a real piece of crap compared to what even an SH novice like me could accomplish. To achieve any kind of decent speed - especially for the CPU emulation - it'd probably be necessary to write the whole thing from scratch in assembly.
Posted: Thu Jan 22, 2009 5:22 pm
by mic_
Just as an example; a function that contains only "return 0;" gets compiled into:
Code: Select all
mov.l r14,@-r15
mov #0,r0
mov r15,r14
mov r14,r15
rts
mov.l @r15+,r14
Plain awesomeness..
That could be reduced by 67%. And it just goes on like that.
Posted: Thu Jan 22, 2009 8:36 pm
by TMorita
mic_ wrote:Just as an example; a function that contains only "return 0;" gets compiled into:
Code: Select all
mov.l r14,@-r15
mov #0,r0
mov r15,r14
mov r14,r15
rts
mov.l @r15+,r14
Plain awesomeness..
That could be reduced by 67%. And it just goes on like that.
GCC is creating a stack frame. You need to use -fomit-frame-pointer to disable this.
Toshi
Posted: Thu Jan 22, 2009 8:43 pm
by mic_
GCC is creating a stack frame.
Yes, I know, it's the same on most processors. That was just an example of the overall (lack of) quality of the code.
Posted: Thu Jan 22, 2009 10:15 pm
by Chilly Willy
mic_ wrote:GCC is creating a stack frame.
Yes, I know, it's the same on most processors. That was just an example of the overall (lack of) quality of the code.
Except that IS quality code... for code with a stack frame. It's not gcc's fault you made no use of the stack frame when you told it to make one. I'm not saying a compiler can beat hand-done assembly, but the code produced is much better than you're saying.
Posted: Fri Jan 23, 2009 7:56 am
by tomaitheous
Awesome project
Let's hope you can get GBC cpu core running full speed as well.
Posted: Fri Jan 23, 2009 8:36 am
by mic_
Code: Select all
Let's hope you can get GBC cpu core running full speed as well.
The CPU is the same, it just runs at twice the clock frequency. I don't see a system with an 8MHz gb-z80 being emulated at full speed on the 32X. Even at normal frequency it's very far from full speed.