Author Topic: Request to include the "FM sound disable" command found on Master Everdrive  (Read 2126 times)

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Offline asdfqwer426

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Game gear is pretty much a portable Master system with a few differences. However they're similar enough that the game gear has no problem controlling and commanding added FM sound hardware that is usually only found on master systems. using an everdrive GG you can play master system games and with an FM board added into the game gear, it plays FM sound just fine.

The issue is when you quit an FM based game when playing FM sound, the everdrive GG does not send the command to port $f2 to disable FM and re-enable PSG (onboard) sound. This results in the everdrive menu making the FM circuit output some random screech, and when you try to load into another game that does not have FM support it will not send the command to disable FM and re-enable PSG, making sound simply not work for non-FM games.

Of course the solution is just to turn off the system and back on again, but I've talked to SMS owners and it sounds like the master everdrive already supports this consideration. I imagine it wouldn't take much to just include that bit of code into the GG OS?

Granted, I've only ever heard or seen one person physically install an FM module into a game gear (it's me...), so this is a pretty niche feature. That said GG modding has really taken off in the last year or two and I wouldn't be surprised to find someone is selling a GG compatible FM module in the next couple years.

Offline GreatFunky

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As a smsx7  and ggx7 owner and from what i know, both everdrives are sharing the same OS.
And i can tell you : the  FM sound disable function is not working on SMS too or at least on SMS 2.

I have a SMS 2 with FM sound board on it and have exactly the issues you describe .

I posted about this 2 years ago and never get any reply 
http://krikzz.com/forum/index.php?topic=9460.0

With hindsight,  maybe I wasn't very clear..... but from what i understood, the function need that you push the reset button and of course there is no reset button on SMS 2 and GG .
So ideally, it would have been nice to have the fm reset at the "back to menu" function.

Offline nuu

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Setting it to the reset button sounds like a very poor idea. Most models of the Master System, including all models with native FM, doesn't have this button. It's not a real reset button like on the Mega Drive either, it's actually an extra controller input button that can be used for anything by the games.

Offline GreatFunky

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Here is the OS changelist :

SMSOS-v1.04 03.12.2019
1)Fixed palette lost during save state in sg-1000 games on gamegear
2)FM chip muting at reset (untested)

I doubt now... i may have misunderstood :-\,  maybe reset button is not needed, but in this case, FM chip muting function is clearly not working.

Unfortunately, i have no SMS1 with reset button + FM board to test and confirm.
« Last Edit: March 06, 2021, 04:42 PM by GreatFunky »

Offline nuu

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I'm not sure what they mean in the changelog, but a hardware "reset" is really the same thing as turning on the system. Try disabling FM in the menu then power cycle the system (turn off, wait 10 seconds then turn on).

Offline asdfqwer426

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see, I thought the GG and master versions did use the same OS and files, but I asked on the master system subreddit and found someone who had a stock SMS and a FM unit installed and it DID disable FM sound correctly on reset. They said they never saw the results I (and now GreatFunky) have both seen - that the FM isn't disabled right. So I assumed that the GG version of the OS left that bit out.

I've been continuing to read up on this stuff a lot more and I might have a guess, but I'm really no expert.

So the audio control port, $F2, seems to react differently based on what system it is on. For instance on a stock Japanese SMS that comes standard with FM, writing 02 seems to disable ALL sound on the system, while many other systems with the FM hardware added instead reacts differently. A mark III with FM for instance disables FM but plays PSG when you write 02 to that port, while a European SMS with the added FM board will continue to play both FM and PSG sound.

I suspect returning to the menu writes 02, which disables all sound on some system, half the sound on others, and none of the sound on some. or something like that. Not sure if a different value would disable the sound properly or not, it might just be a side effect of how these boards interact together.

Offline nuu

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On the Mark III you can enable either PSG or FM sound (if FM Unit is connected), but not both at the same time. On the Japanese SMS you can enable either, both or disable both. But no game enables both (except the SMS BIOS screen's BGM) to maintain compatibility with the Mark III. On a non-Japanese SMS it depends on how you do the FM chip mod, if you go the Mark III route, the SMS route or something else.
https://www.smspower.org/Development/AudioControlPort