Search found 2441 matches
- Thu Sep 23, 2021 1:22 am
- Forum: Cartridge
- Topic: Change RAM, CRAM from addon
- Replies: 2
- Views: 11836
Re: Change RAM, CRAM from addon
Cartslot is slave only with no means to do bus mastering (it cannot initiate writes to the console, only receive them) so you'll need software help. One way is to hijack frame interrupt, do your thing in it and then run the original handler, but it might break timing sensitive games.
- Sun Sep 12, 2021 1:49 am
- Forum: Video Display Processor
- Topic: CRAM question
- Replies: 1
- Views: 6220
Re: CRAM question
CRAM is a physical array of 64 x 9 bits on the silicon, the unused bits in the data port are simply not connected to the actual memory at least as far as writes are concerned. These unused bits can be anything, they simply are ignored when writes are done. For reads I am unsure what will happen, are...
- Wed Aug 11, 2021 10:26 pm
- Forum: Video Display Processor
- Topic: VDP Resolution
- Replies: 3
- Views: 6288
Re: VDP Resolution
A TV often does what is referred to as the overscan, which means that only some part of the full image gets shown on the physical screen. There is no direct pixel mapping going on and because of this a game is not supposed to put anything in the edges of the screen since they are simply not guarante...
- Wed Aug 11, 2021 10:11 pm
- Forum: Megadrive/Genesis
- Topic: TMSS
- Replies: 6
- Views: 8664
Re: TMSS
TMSS ROM inside the MD (if present) checks for presence of "SEGA" or " SEGA" at $000100 in your ROM, if found it will boot your ROM. Otherwise it just enters an idle loop and the ROM will not be started and you won't get to see the "produced by...." screen. TMSS ROM has no relation to the $A14000 re...
- Tue Aug 10, 2021 8:45 pm
- Forum: SGDK
- Topic: 68k based PCM Audio mixer for YM2612
- Replies: 7
- Views: 9038
Re: 68k based PCM Audio mixer for YM2612
You have line and frame interrupts so that is not a problem, though Z80 only gets frame interrupt. Yes, Z80 can do it, and you are supposed to use Z80 for it (and all the sound tasks in general). You cannot send data to Z80 RAM without stopping the Z80 so updating any buffers while also doing playba...
- Tue Aug 10, 2021 9:26 am
- Forum: SGDK
- Topic: 68k based PCM Audio mixer for YM2612
- Replies: 7
- Views: 9038
Re: 68k based PCM Audio mixer for YM2612
You're in for a big disappointment because the PCM on MD doesn't work anywhere near like it does on the ST. You just have one IO port in the YM that you must manually feed with new data, all timing is up to you as there is no automatic sample fetching and you don't have any regular interrupt to do t...
- Mon Aug 02, 2021 4:57 am
- Forum: Video Display Processor
- Topic: VDP Resolution
- Replies: 3
- Views: 6288
Re: VDP Resolution
224 vs 240 has 8 pixel borders in top and bottom, but 256 vs 320 is filling the screen horizontally, with non square pixels in 256 (just like Master System and (S)NES stuff. Pixels are longer in the video signal output by VDP compared to shorter ones of 320, there's no really good ways to cleanly ap...
- Wed Jul 28, 2021 5:18 pm
- Forum: Megadrive/Genesis
- Topic: TMSS
- Replies: 6
- Views: 8664
Re: TMSS
The SEGA write existed before TMSS ROM did, though it became actually functional with the introduction of TMSS with VA5/6 MD1 hardware. It was part of a copyright thing that all ROMs must have in them prior to introduction of the TMSS ROM which did its own verification on top while retaining the stu...
- Mon Jul 26, 2021 7:25 pm
- Forum: Megadrive/Genesis
- Topic: TMSS
- Replies: 6
- Views: 8664
Re: TMSS
Not doing the SEGA write results in VDP not cooperating with you on hardware that requires this write and that's what the version register will tell you if it is necessary to do so. The value is hardcoded in the ASIC and cannot be influenced by normal means, there's only 0000 and 0001 in all the exi...
- Mon Jul 12, 2021 4:03 am
- Forum: Megadrive/Genesis
- Topic: VRAM write macro $3FFF mask
- Replies: 3
- Views: 5991
Re: VRAM write macro $3FFF mask
This stems from TMS99xx and SMS VDPs, which only had 16bit command words with 16KB VRAM. MD VDP extended the command words to 32bits and the new address bits (and few extra things) are in the second part, while first part is kept like the older stuff. There's some playroom with how you arrange the b...
- Mon Jun 28, 2021 11:04 am
- Forum: Megadrive/Genesis
- Topic: Problem getting animation working on Sega Genesis.
- Replies: 2
- Views: 5500
Re: Problem getting animation working on Sega Genesis.
It is quite possible your frame is so large that it overwrites non-graphics parts in the VRAM, such as tilemaps or some other things that must coexist there along with the tiles themselves.
- Fri Apr 09, 2021 9:59 am
- Forum: Megadrive/Genesis
- Topic: VDP FIFO and DMA questions
- Replies: 3
- Views: 46926
Re: VDP FIFO and DMA questions
Half lines are part of the video signal, around VSYNC signal. They existed to allow early sync separation circuits to reliably produce a VSYNC pulse using a simple integrator circuit on extracted CSYNC signal. Two halflines make a whole line. The 16 and 17 are Hsync length in the half lines, un pixe...
- Fri Apr 09, 2021 3:25 am
- Forum: Megadrive/Genesis
- Topic: VDP FIFO and DMA questions
- Replies: 3
- Views: 46926
Re: VDP FIFO and DMA questions
Here is all there is to know about MD video output timings, from my unreleased MD VDP doc. Things are not fully finished around half lines parts, the number lines mean pixels counts during half lines, one number while in sync period, other outside sync. 888aaa999 ones mean pixel patterns during sync...
- Sat Apr 03, 2021 10:56 pm
- Forum: Super 32X
- Topic: Reset and VRES
- Replies: 2
- Views: 6409
Re: Reset and VRES
I imagine you modify stack to have a new return address prior to exiting the interrupt and probably force caches to be flushed too.
- Thu Mar 25, 2021 8:37 am
- Forum: Super 32X
- Topic: Questions on emulating the 32X
- Replies: 14
- Views: 229887
Re: Questions on emulating the 32X
Is this the case only when it's the backdrop color (no background/sprites), or when it's the backdrop color OR palette color 0 (from a background or sprite)? VDP never renders color 0 of any palette when drawing BGs and sprites on the screen, it is the backdrop color that is output when a particula...