Search found 599 matches

by Mask of Destiny
Wed Mar 10, 2021 1:15 am
Forum: Video Display Processor
Topic: VDP 128Kb Extended VRAM mode
Replies: 44
Views: 43723

Re: VDP 128Kb Extended VRAM mode

BlastEm is the only emulator to (partially ?) emulate it so be sure to use this emulator which is the most accurate by far when you are testing obscures things like that :) Yeah, my support is fairly minimal at the moment. I emulate 128KB mode's impact on the FIFO, but I don't support actually havi...
by Mask of Destiny
Tue Feb 16, 2021 6:25 pm
Forum: Megadrive/Genesis
Topic: Version Register
Replies: 6
Views: 1832

Re: Version Register

Right, 315-5402 is special, it shows no TMSS when in JP mode, while TMSS is shown in EN mode. I did notice the freezing problem with TMSS as I tried to dump the ROM when accessing the banking register... Interesting. Were systems with the 315-5402 were actually released outside of Japan, or is this...
by Mask of Destiny
Mon Feb 15, 2021 11:00 pm
Forum: Megadrive/Genesis
Topic: Version Register
Replies: 6
Views: 1832

Re: Version Register

Yeah, it's zero on a 315-5309 IO chip and 1 on the 315-5402 (integrated IO chip and arbiter on a VA5) and all later IO chip versions. The 315-5402 doesn't have a full TMSS implementation though. Attempting to bank in the TMSS ROM will lock the machine (assuming because !DTACK is not being asserted f...
by Mask of Destiny
Wed Feb 10, 2021 6:41 am
Forum: Megadrive/Genesis
Topic: 68K Memory access
Replies: 9
Views: 2251

Re: 68K Memory access

In what sequence does it? 1) Address + 0 2) Address + 2 Or 1) Address + 2 2) Address + 0 It depends. Reads are always done the first way. Writes are usually done the first way as well, but the destination of a move instruction is written the second way UNLESS it's using the predecrement addressing ...
by Mask of Destiny
Thu Jan 21, 2021 6:57 pm
Forum: Megadrive/Genesis
Topic: 68K Memory access
Replies: 9
Views: 2251

Re: 68K Memory access

The cart can't stop the hardware in the console from responding, so it is generally not proper to respond to a read from an address that the console already does. If you want to be compatible with the Sega CD and 32X, you also need to avoid the address ranges they use. The Teradrive additionally use...
by Mask of Destiny
Wed Sep 02, 2020 2:30 am
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 9131

Re: List of every detectable difference in Mega Drive revisions?

That's something I didn't know, I mainly only commented among the actual consoles (except MD2 VA2, which I would like to get and a VA0 MD1). Discrete YM3438 has longer busy bit cycle from what I remember reading from nukeYKT core notes, compared to 2612 and ASIC which would be another way to detect...
by Mask of Destiny
Sat Aug 22, 2020 2:50 am
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 9131

Re: List of every detectable difference in Mega Drive revisions?

TmEE co.(TM) wrote:
Fri Aug 21, 2020 5:30 pm
YM3438 only appeared as a block integrated in the MD2 ASIC, which first appeared in MD1 VA7 (the awful sounding MD1s lol).
The Teradrive has a discrete YM3438 and in the other direction there are the MD2 VA2/VA2.3 which have a discrete YM2612.
by Mask of Destiny
Thu Aug 20, 2020 5:26 am
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 9131

Re: List of every detectable difference in Mega Drive revisions?

These are the detectable differences I am personally aware of * Open bus behavior of the Z80 bus (MD1 VA3 and later always return FF, earlier consoles will return last value read) * Discrete YM2612 vs Integrated YM3438 (the latter allows status to be properly read on all addresses) * Open bus behavi...
by Mask of Destiny
Fri May 31, 2019 8:14 pm
Forum: Mega/SegaCD
Topic: Bike shedding a new CD-ROM format
Replies: 20
Views: 12798

Re: Bike shedding a new CD-ROM format

I can't find good documentation on what CHD actually does with CDs. So in it's most basic form a CHD is a series of compressed "hunks" of data. Hunks are relatively small (512KB max supposedly) and are compressed individually to allow reasonably random access. For CDs, extra metadata is stored to h...
by Mask of Destiny
Thu May 30, 2019 9:32 pm
Forum: Mega/SegaCD
Topic: Bike shedding a new CD-ROM format
Replies: 20
Views: 12798

Re: Bike shedding a new CD-ROM format

For most "normal" CD-ROM imaging needs, I kind of feel like MAME's CHD format is probably the right way to go. The lack of proper documentation is a bummer, but it handles multi-track data well and can store raw F1 frames + subcode data. It also supports lossless compression of tracks including FLAC...
by Mask of Destiny
Sun Apr 28, 2019 4:06 pm
Forum: Megadrive/Genesis
Topic: Z80 bus + I/O mapping redux
Replies: 7
Views: 6961

Re: Z80 bus + I/O mapping redux

As promised, here's that test ROM and here's the source . * a00000-a0ffff => [8-bit bus] Z80 (A15 is ignored) So this is actually a funny one. On the 68K side, all 16 data lines are connected (via the IO chip because apparently they ran out of pins on the bus arbiter, lol), but the bus being connect...
by Mask of Destiny
Fri Apr 26, 2019 3:18 pm
Forum: Megadrive/Genesis
Topic: Z80 bus + I/O mapping redux
Replies: 7
Views: 6961

Re: Z80 bus + I/O mapping redux

bgvanbur states the Z80 can write to 68K main-CPU RAM (e00000-ffffff), but reads return 0xff. It's further comments that reads return different values on different systems. Stef finds that writes do not work. Steve Snake says they used to on the earliest models. For what it's worth, I have a test R...
by Mask of Destiny
Wed Apr 24, 2019 4:21 pm
Forum: Demos
Topic: MD-NICCC - a 3D Mega Drive experience by TiTAN
Replies: 56
Views: 33081

Re: MD-NICCC - a 3D Mega Drive experience by TiTAN

Stef wrote:
Wed Apr 24, 2019 2:40 pm
Are you speaking about Starfox on SNES or something else ?
Pretty sure Sik is talking about the SNES port of the ST-NICC demo which was also released at Revision this year.
by Mask of Destiny
Fri Apr 05, 2019 9:59 pm
Forum: Demos
Topic: Tänzer, a "ninja" game (Dev Diary thread)
Replies: 290
Views: 101673

Re: Tänzer, a "ninja" game (Dev Diary thread)

notaz, what revision is your MD1?
by Mask of Destiny
Wed Apr 03, 2019 6:44 pm
Forum: Cartridge
Topic: EEPROM mapping for homebrew
Replies: 9
Views: 6741

Re: EEPROM mapping for homebrew

My 2 cents: standardizing the mapping (i.e. which address and which I2C bits are connected where) is good, but I think allowing the size to be specified in the header is desirable. It might make sense to pick a single "mode" (i.e. how the address is sent), but from my perspective supporting any of t...