byuu says:
Added VDP sprite rendering. Can't get any games far enough in to see if
it actually works. So in other words, it doesn't work at all and is 100%
completely broken.
Also added 68K exceptions and interrupts. So far only the VDP interrupt
is present. It definitely seems to be firing in commercial games, so
that's promising. But the implementation is almost certainly completely
wrong. There is fuck all of nothing for documentation on how interrupts
actually work. I had to find out the interrupt vector numbers from
reading the comments from the Sonic the Hedgehog disassembly. I have
literally no fucking clue what I0-I2 (3-bit integer priority value in
the status register) is supposed to do. I know that Vblank=6, Hblank=4,
Ext(gamepad)=2. I know that at reset, SR.I=7. I don't know if I'm
supposed to block interrupts when I is >, >=, <, <= to the interrupt
level. I don't know what level CPU exceptions are supposed to be.
Also implemented VDP regular DMA. No idea if it works correctly since
none of the commercial games run far enough to use it. So again, it's
horribly broken for usre.
Also improved VDP fill mode. But I don't understand how it takes
byte-lengths when the bus is 16-bit. The transfer times indicate it's
actually transferring at the same speed as the 68K->VDP copy, strongly
suggesting it's actually doing 16-bit transfers at a time. In which case,
what happens when you set an odd transfer length?
Also, both DMA modes can now target VRAM, VSRAM, CRAM. Supposedly there's
all kinds of weird shit going on when you target VSRAM, CRAM with VDP
fill/copy modes, but whatever. Get to that later.
Also implemented a very lazy preliminary wait mechanism to to stall out
a processor while another processor exerts control over the bus. This
one's going to be a major work in progress. For one, it totally breaks
the model I use to do save states with libco. For another, I don't
know if a 68K->VDP DMA instantly locks the CPU, or if it the CPU could
actually keep running if it was executing out of RAM when it started
the DMA transfer from ROM (eg it's a bus busy stall, not a hard chip
stall.) That'll greatly change how I handle the waiting.
Also, the OSS driver now supports Audio::Latency. Sound should be
even lower latency now. On FreeBSD when set to 0ms, it's absolutely
incredible. Cannot detect latency whatsoever. The Mario jump sound seems
to happen at the very instant I hear my cherry blue keyswitch activate.
byuu says:
Changelog:
- 68K: fixed bug that affected BSR return address
- VDP: added very preliminary emulation of planes A, B, W (W is
entirely broken though)
- VDP: added command/address stuff so you can write to VRAM, CRAM,
VSRAM
- VDP: added VRAM fill DMA
I would be really surprised if any commercial games showed anything at
all, so I'd probably recommend against wasting your time trying, unless
you're really bored :P
Also, I wanted to add: I am accepting patches\! So if anyone wants to
look over the 68K core for bugs, that would save me untold amounts of
time in the near future :D
byuu says:
Changelog:
- pulled the (u)intN type aliases into higan instead of leaving them
in nall
- added 68K LINEA, LINEF hooks for illegal instructions
- filled the rest of the 68K lambda table with generic instance of
ILLEGAL
- completed the 68K disassembler effective addressing modes
- still unsure whether I should use An to decode absolute
addresses or not
- pro: way easier to read where accesses are taking place
- con: requires An to be valid; so as a disassembler it does a
poor job
- making it optional: too much work; ick
- added I/O decoding for the VDP command-port registers
- added skeleton timing to all five processor cores
- output at 1280x480 (needed for mixed 256/320 widths; and to handle
interlace modes)
The VDP, PSG, Z80, YM2612 are all stepping one clock at a time and
syncing; which is the pathological worst case for libco. But they also
have no logic inside of them. With all the above, I'm averaging around
250fps with just the 68K core actually functional, and the VDP doing a
dumb "draw white pixels" loop. Still way too early to tell how this
emulator is going to perform.
Also, the 320x240 mode of the Genesis means that we don't need an aspect
correction ratio. But we do need to ensure the output window is a
multiple 320x240 so that the scale values work correctly. I was
hard-coding aspect correction to stretch the window an additional \*8/7.
But that won't work anymore so ... the main higan window is now 640x480,
960x720, or 1280x960. Toggling aspect correction only changes the video
width inside the window.
It's a bit jarring ... the window is a lot wider, more black space now
for most modes. But for now, it is what it is.
Tim Allen