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View topic - [Demo] Bad Apple!! (for Mark III + FM Unit)

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  • Joined: 26 Feb 2020
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[Demo] Bad Apple!! (for Mark III + FM Unit)
Post Posted: Mon Jun 13, 2022 7:48 pm
Last edited by 2Tie on Fri Jun 17, 2022 2:12 am; edited 1 time in total
Here's a homebrew I made that utilizes the FM test register ($0F) to play a prepped waveform, and tms graphics II (mode 2) to stream 1bpp full motion video at 30fps on an NTSC system. I designed it to discern if it's running on SMS and lock up if so; this can be disabled by replacing a cp b instruction with cp a, but I haven't tested if this works on master systems. This demo works fine on my setup, but my Mark III sometimes needs a couple restarts to run anything properly. I'd be interested if other Mark III users could confirm it works! Neither audio nor video should work on Power Base Converter or Mega Everdrive.

Also, the ROM is 4MB, but you can safely trim the end down to 1MB or 512KB to fit on smaller flash carts; it just won't play as much.

I'm also mildly disappointed that I could only fit about a third of the whole video into the SEGA Mapper's space limit; with my focus on fidelity and speed, space was the aspect that suffered the most.
rotten.zip (1.9 MB)
the demo

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  • Joined: 05 Sep 2013
  • Posts: 3762
  • Location: Stockholm, Sweden
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Post Posted: Tue Jun 14, 2022 11:28 am
2Tie wrote
As far as I know, my particular method doesn't work the same way on either type of SMS VDPs, so I added a couple checks at the start to discern if it's running on SMS and lock up if so.


Can you please give more detail about this? I'm curious!
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  • Joined: 26 Feb 2020
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Post Posted: Thu Jun 16, 2022 11:47 pm
sverx wrote
2Tie wrote
As far as I know, my particular method doesn't work the same way on either type of SMS VDPs, so I added a couple checks at the start to discern if it's running on SMS and lock up if so.


Can you please give more detail about this? I'm curious!


So, turns out my conclusions on this were false; I was cautioned about the mask bits in the VDP registers when i posted a test rom, and that coupled with the very limited documentation of the TMS modes in the dev pages led me to believe that the VDPs apply the mask bits to any modes as defined on the registers page, while my Mark III (and Emulicious) didn't. Couple this with my test rom seeming to have different behaviour on calindro's sms1 vs sms2 and that reinforced it for me.

The actual behaviour is that the mask bits only apply to mode 4, at least as far as i've tested (and makes sense, don't want to break compat with sg games). I'll update my starting post to reflect this, and try and clarify the dev wiki a bit on the matter.
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Post Posted: Fri Jun 17, 2022 8:23 am
Mark IIIs have the same VDP as the SMS (the first revision) so I wouldn't expect any difference here...
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