Search found 615 matches

by Mask of Destiny
Wed Oct 10, 2018 6:42 pm
Forum: Megadrive/Genesis
Topic: Bus Arbiter and IO Chip Access
Replies: 28
Views: 37852

Re: Bus Arbiter and IO Chip Access

Did some probing on my model 1 va2. It has a 5308 arbiter, a 5309 IO chip and a 5345. For what it's worth, we have the schematics for the VA3 . Main difference from your VA2 is that the 5345 (EDCLK generator, probably just a PAL or GAL) has been integrated into the bus arbiter (5308) and given the ...
by Mask of Destiny
Tue Oct 09, 2018 11:48 pm
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 70
Views: 130212

Re: Cart Design Questions

When writing 8Bit numbers to even addresses, is pin B28 (lower byte write) taken low and pin B29 left high, and for odd addresses B28 is left high and B29 is taken low? Or visa versa? Or does it work differently? !LDSW (B28) goes low (which is the "active" level) for writes to odd addresses and !UD...
by Mask of Destiny
Fri Oct 05, 2018 8:37 pm
Forum: Megadrive/Genesis
Topic: Aggregating Community Research
Replies: 12
Views: 14382

Re: Aggregating Community Research

Bumping this as I've added a number of additional links to the OP. I'm sure there's stuff I've missed, so feel free to suggest additions here.
by Mask of Destiny
Mon Sep 24, 2018 8:18 pm
Forum: Megadrive/Genesis
Topic: 68k edge case: btst dN,#immed
Replies: 12
Views: 16697

Re: 68k edge case: btst dN,#immed

I then checked Galibert's microcode dump (see here , or here for all data he has) and confirmed the same thing. Oooh, I didn't realize he had gotten that far with decoding the microcode. I'll definitely have to check that out when I get time. The TL;DR version is: "btst dN,#immed8" shares microcode...
by Mask of Destiny
Wed Sep 19, 2018 11:25 pm
Forum: Sound
Topic: Regarding the YM3438 on the Mega Drive...
Replies: 11
Views: 16228

Re: Regarding the YM3438 on the Mega Drive...

l_oliveira wrote:
Wed Sep 19, 2018 9:11 pm
If it is not done that way, the YM3438 actually fails to work on a lot of games.
Which games? I haven't heard of widespread compatibility issues with the Teradrive (which as I previously mentioned has a discrete YM3438), but I'd happy to test some if you know specific games that have problems.
by Mask of Destiny
Sun Sep 16, 2018 4:34 pm
Forum: Sound
Topic: Regarding the YM3438 on the Mega Drive...
Replies: 11
Views: 16228

Re: Regarding the YM3438 on the Mega Drive...

Sik wrote:
Sun Sep 16, 2018 4:06 pm
This reminds me, the Mega Drive never had a discrete YM3438 (somebody pointed it out to me last night after I had posted >.>).
The Teradrive has an actual YM3438.
by Mask of Destiny
Thu Aug 09, 2018 8:16 pm
Forum: Megadrive/Genesis
Topic: Teradrive Hardware Info
Replies: 3
Views: 8229

Re: Teradrive Hardware Info

Wow, good job with this! Thanks! I always wanted to investigate this hardware more, but never found the time. Still quite a few unknowns if you suddenly find yourself with a bunch of free time :wink: Happy to share test code and/or IDA disassembly projects if that happens (though I know how hard fr...
by Mask of Destiny
Thu May 31, 2018 5:17 pm
Forum: Megadrive/Genesis
Topic: Teradrive Hardware Info
Replies: 3
Views: 8229

Teradrive Hardware Info

First, let me start with a big thanks to Nemesis and piroxilin for providing Teradrive disk images and firmware images respectively. Having easy access to software/firmware to reverse was a big help. Now for the info I've figured out: M68K Memory Map (standard MD hardware omitted) 000000 - ??????: B...
by Mask of Destiny
Fri Apr 27, 2018 6:16 pm
Forum: Megadrive/Genesis
Topic: Struct maros/syntax and naming conventions
Replies: 6
Views: 8767

Re: Struct maros/syntax and naming conventions

You should put a non-zero number after the rs.b/rs.w/rs.l as that's the number of elements of that size you're allocating. Not sure if that's causing your syntax error, but you definitely won't get the right results with zero.
by Mask of Destiny
Thu Mar 01, 2018 7:46 pm
Forum: Megadrive/Genesis
Topic: Where do I start? I'm seeking technical documents.
Replies: 40
Views: 27411

Re: Where do I start? I'm seeking technical documents.

sverx wrote:
Tue Feb 27, 2018 2:57 pm
Where can I read more details about this? (yeah, I know it's an advanced topic, but I'm curious :lol: )
Check out this thread and the linked documentation.
by Mask of Destiny
Mon Feb 26, 2018 6:45 pm
Forum: Megadrive/Genesis
Topic: Where do I start? I'm seeking technical documents.
Replies: 40
Views: 27411

Re: Where do I start? I'm seeking technical documents.

I wonder if the last line is correct - I mean, I can't display color 0 of any of the 4 palettes even if I use the tiles in a background? It is correct; however, the backdrop color (i.e. what's drawn in the borders or if all the layers above it are transparent) can be any of the 64 CRAM entries, inc...
by Mask of Destiny
Wed Jan 10, 2018 8:03 am
Forum: Controls
Topic: IO Support Header Values
Replies: 1
Views: 8099

IO Support Header Values

I was wondering what values were legal for the IO support field in the standard Sega ROM header so I poked around a bit. This page from the official docs gives quite a few of them, but omits newer peripherals. Looking at the games in my collection I was able to fill in a few gaps and come up with th...
by Mask of Destiny
Tue Nov 21, 2017 9:25 pm
Forum: Megadrive/Genesis
Topic: Sprite List Code Messed Up
Replies: 28
Views: 17723

Re: Sprite List Code Messed Up

Hm. I wonder if anyone ever transcribed the whole microcode portion of US4325121... having it as a searchable document would be a lot better, as well as less error prone because of how bad the scan is. I've got just shy of 100 transcribed which is pretty far from complete, though it probably covers...
by Mask of Destiny
Tue Oct 24, 2017 8:38 pm
Forum: Controls
Topic: XE-1AP
Replies: 4
Views: 79995

Re: XE-1AP

Interesting. The comment does seem to be in line with what the code does (saves the 12 nibbles as 12 bytes in the buffer and pulls the A,B,A',B' state from the 11th byte rather than the 12th). Though it also suggests that A,B,C,D comes in the first nibble with E1,E2,Start,Select in the second. It lo...
by Mask of Destiny
Tue Oct 24, 2017 7:12 am
Forum: Controls
Topic: XE-1AP
Replies: 4
Views: 79995

XE-1AP

So I managed to find an XE-1AP while I was in Japan recently and I wrote a little test ROM to better characterize its behavior. First off, big thanks to Eke for emulating this peripheral in Genesis Plus GX as having some idea how this peripheral was supposed to work was a huge time saver when writin...