Search found 2426 matches

by TmEE co.(TM)
Thu Sep 23, 2021 1:22 am
Forum: Cartridge
Topic: Change RAM, CRAM from addon
Replies: 2
Views: 521

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.
by TmEE co.(TM)
Sun Sep 12, 2021 1:49 am
Forum: Video Display Processor
Topic: CRAM question
Replies: 1
Views: 688

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...
by TmEE co.(TM)
Wed Aug 11, 2021 10:26 pm
Forum: Video Display Processor
Topic: VDP Resolution
Replies: 3
Views: 1154

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...
by TmEE co.(TM)
Wed Aug 11, 2021 10:11 pm
Forum: Megadrive/Genesis
Topic: TMSS
Replies: 6
Views: 1164

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...
by TmEE co.(TM)
Tue Aug 10, 2021 8:45 pm
Forum: SGDK
Topic: 68k based PCM Audio mixer for YM2612
Replies: 7
Views: 767

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...
by TmEE co.(TM)
Tue Aug 10, 2021 9:26 am
Forum: SGDK
Topic: 68k based PCM Audio mixer for YM2612
Replies: 7
Views: 767

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...
by TmEE co.(TM)
Mon Aug 02, 2021 4:57 am
Forum: Video Display Processor
Topic: VDP Resolution
Replies: 3
Views: 1154

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...
by TmEE co.(TM)
Wed Jul 28, 2021 5:18 pm
Forum: Megadrive/Genesis
Topic: TMSS
Replies: 6
Views: 1164

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...
by TmEE co.(TM)
Mon Jul 26, 2021 7:25 pm
Forum: Megadrive/Genesis
Topic: TMSS
Replies: 6
Views: 1164

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...
by TmEE co.(TM)
Mon Jul 12, 2021 4:03 am
Forum: Megadrive/Genesis
Topic: VRAM write macro $3FFF mask
Replies: 3
Views: 813

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...
by TmEE co.(TM)
Mon Jun 28, 2021 11:04 am
Forum: Megadrive/Genesis
Topic: Problem getting animation working on Sega Genesis.
Replies: 2
Views: 898

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.
by TmEE co.(TM)
Fri Apr 09, 2021 9:59 am
Forum: Megadrive/Genesis
Topic: VDP FIFO and DMA questions
Replies: 3
Views: 2475

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...
by TmEE co.(TM)
Fri Apr 09, 2021 3:25 am
Forum: Megadrive/Genesis
Topic: VDP FIFO and DMA questions
Replies: 3
Views: 2475

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...
by TmEE co.(TM)
Sat Apr 03, 2021 10:56 pm
Forum: Super 32X
Topic: Reset and VRES
Replies: 2
Views: 1750

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.
by TmEE co.(TM)
Thu Mar 25, 2021 8:37 am
Forum: Super 32X
Topic: Questions on emulating the 32X
Replies: 14
Views: 3713

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...