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by Mask of Destiny
Sat Dec 01, 2018 4:13 am
Forum: Exodus
Topic: Genesis 68K bus timing
Replies: 6
Views: 292

Re: Genesis 68K bus timing

Here's a small collection of captures of various types of bus interactions. They are in Open Logic Sniffer Project format. Explanations below: direct_color_dma.olp - Capture of the start of 68K->VDP DMA from one of Chilly WIlly's Direct Color DMA samples (note that !CAS and !RAS here refer to VRAM !...
by Mask of Destiny
Fri Nov 30, 2018 6:33 pm
Forum: Exodus
Topic: Genesis 68K bus timing
Replies: 6
Views: 292

Re: Genesis 68K bus timing

I am searching hardware level information about the interface with the 68K. Do you know if anybody performed logic analyzer traces showing the timing of the clock and the bus control signals? Yes. 68K clock is always the master clock/7 (unless you count the Teradrive which can also run the CPU at 1...
by Mask of Destiny
Tue Nov 20, 2018 7:30 pm
Forum: Megadrive/Genesis
Topic: Looping access from 68K and Z80
Replies: 25
Views: 1024

Re: Looping access from 68K and Z80

My breakout boards cam it but sadly the pads for the pins on the chip were just a tad too short. New boards ordered but with the US holiday coming up it’ll be 10-14 days before I get them back. In the meantime, I found a semiconductor seller that had some genesis chips in stock so I picked up a cou...
by Mask of Destiny
Thu Oct 11, 2018 7:12 pm
Forum: Megadrive/Genesis
Topic: Bus Arbiter and IO Chip Access
Replies: 25
Views: 1521

Re: Bus Arbiter and IO Chip Access

It would be interesting to verify is there are any differences regarding EDCLK between MD VA1 and late rmodels since it seems VA1 (and likely VA0) is using an earlier version of 315-5345 chip (see 315-5339 description here: http://www.tmeeco.eu/SMD/MD1VA1_315-5339.jpg) which does not use VCLK (and ...
by Mask of Destiny
Thu Oct 11, 2018 7:18 am
Forum: Megadrive/Genesis
Topic: Bus Arbiter and IO Chip Access
Replies: 25
Views: 1521

Re: Bus Arbiter and IO Chip Access

EDCLK: This signal is 0/floating (wasnt a very clean 0) when /SRES, /M3 or /HSYNC are asserted(0). Otherwise it seems to be MCLK/4. (I tested with a 5k signal. Got a 1.25K out. I thought this this should /5, maybe it doesn't like the slow speed?) Does not seem to be affected by anything else. It sh...
by Mask of Destiny
Wed Oct 10, 2018 6:42 pm
Forum: Megadrive/Genesis
Topic: Bus Arbiter and IO Chip Access
Replies: 25
Views: 1521

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: 26
Views: 2197

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: 3262

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: 11
Views: 1081

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: 1054

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: 1054

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: 1035

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: 1035

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: 991

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: 4180

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.