SpritesMind.Net

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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.

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 ...

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 ...

I imagine you modify stack to have a new return address prior to exiting the interrupt and probably force caches to be flushed too.

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 ...

VDP outputs a signal called !YS which is active when nothing/backdrop color is being output, it is present on cartslot along with !HSYNC and !VSYNC signals and 32X uses them for image alignment and composition purposes.

There are 3 signals involved in controlling if 32X or MD RGB signal is switched ...

I have only ever seen the chip in Japanese machines, never in EU or US ones. I have the chip transplanted onto an EU VA5/6 board and the region mod changes TMSS behaviour. l_oliveira has some observations done too in past, telling that "SEGA" write is unnecessary when the language setting is in JP ...

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...

The value is not adjustable externally.