byuu says:
Changelog:
- new md/bus/ module for bus reads/writes
- abstracts byte/word accesses wherever possible (everything but
RAM; forces all but I/O to word, I/O to byte)
- holds the system RAM since that's technically not part of the
CPU anyway
- added md/controller and md/system/peripherals
- added emulation of gamepads
- added stub PSG audio output (silent) to cap the framerate at 60fps
with audio sync enabled
- fixed VSRAM reads for plane vertical scrolling (two bugs here: add
instead of sub; interlave plane A/B)
- mask nametable read offsets (can't exceed 8192-byte nametables
apparently)
- emulated VRAM/VSRAM/CRAM reads from VDP data port
- fixed sprite width/height size calculations
- added partial emulation of 40-tile per scanline limitation (enough
to fix Sonic's title screen)
- fixed off-by-one sprite range testing
- fixed sprite tile indexing
- Vblank happens at Y=224 with overscan disabled
- unsure what happens when you toggle it between Y=224 and Y=240
... probably bad things
- fixed reading of address register for ADDA, CMPA, SUBA
- fixed sign extension for MOVEA effect address reads
- updated MOVEM to increment the read addresses (but not writeback)
for (aN) mode
With all of that out of the way, we finally have Sonic the Hedgehog
(fully?) playable. I played to stage 1-2 and through the special stage,
at least. EDIT: yeah, we probably need HIRQs for Labyrinth Zone.
Not much else works, of course. Most games hang waiting on the Z80, and
those that don't (like Altered Beast) are still royally screwed. Tons of
features still missing; including all of the Z80/PSG/YM2612.
A note on the perihperals this time around: the Mega Drive EXT port is
basically identical to the regular controller ports. So unlike with the
Famicom and Super Famicom, I'm inheriting the exension port from the
controller class.
byuu says:
Changelog:
- 68K: fixed NEG/NEGX operand order
- 68K: fixed bug in disassembler that was breaking trace logging
- VDP: improved sprite rendering (still 100% broken)
- VDP: added horizontal/vertical scrolling (90% broken)
Forgot:
- 68K: fix extension word sign bit on indexed modes for disassembler
as well
- 68K: emulate STOP properly (use r.stop flag; clear on IRQs firing)
I'm really wearing out fast here. The Genesis documentation is somehow
even worse than Game Boy documentation, but this is a far more complex
system.
It's a massive time sink to sit here banging away at every possible
combination of how things could work, only to see no positive
improvements. Nothing I do seems to get sprites to do a goddamn thing.
squee says the sprite Y field is 10-bits, X field is 9-bits. genvdp says
they're both 10-bits. BlastEm treats them like they're both 10-bits,
then masks off the upper bit so it's effectively 9-bits anyway.
Nothing ever bothers to tell you whether the horizontal scroll values
are supposed to add or subtract from the current X position. Probably
the most basic detail you could imagine for explaining horizontal
scrolling and yet ... nope. Nothing.
I can't even begin to understand how the VDP FIFO functionality works,
or what the fuck is meant by "slots".
I'm completely at a loss as how how in the holy hell the 68K works with
8-bit accesses. I don't know whether I need byte/word handlers for every
device, or if I can just hook it right into the 68K core itself. This
one's probably the most major design detail. I need to know this before
I go and implement the PSG/YM2612/IO ports-\>gamepads/Z80/etc.
Trying to debug the 68K is murder because basically every game likes to
start with a 20,000,000-instruction reset phase of checksumming entire
games, and clearing out the memory as agonizingly slowly as humanly
possible. And like the ARM, there's too many registers so I'd need three
widescreen monitors to comfortably view the entire debugger output lines
onscreen.
I can't get any test ROMs to debug functionality outside of full games
because every **goddamned** test ROM coder thinks it's acceptable to tell
people to go fetch some toolchain from a link that died in the late '90s
and only works on MS-DOS 6.22 to build their fucking shit, because god
forbid you include a 32KiB assembled ROM image in your fucking archives.
... I may have to take a break for a while. We'll see.
byuu says:
Sorry, two WIPs in one day. Got excited and couldn't wait.
Changelog:
- ADDQ, SUBQ shouldn't update flags when targeting an address register
- ADDA should sign extend effective address reads
- JSR was pushing the PC too early
- some improvements to 8-bit register reads on the VDP (still needs
work)
- added H/V counter reads to the VDP IO port region
- icarus: added support for importing Master System and Game Gear ROMs
- tomoko: added library sub-menus for each manufacturer
- still need to sort Game Gear after Mega Drive somehow ...
The sub-menu system actually isn't all that bad. It is indeed a bit more
annoying, but not as annoying as I thought it was going to be. However,
it looks a hell of a lot nicer now.
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