Author Topic: Save states on SD2Snes  (Read 25803 times)

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Offline nuu

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Re: Save states on SD2Snes
« Reply #60 on: March 01, 2020, 01:09 PM »
No it's only a problem with the SNES APU. The MSU1 is part of the flashcartridge so there is no problem for it to preserve the state of it.

Offline WaveRacer

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Re: Save states on SD2Snes
« Reply #61 on: March 02, 2020, 11:57 AM »
I thought the plan for the FPGA APU would be to mirror any sound commands issued to it so it runs in tandem with the real SPC chip in the SNES, it wouldn't then actually output any sound (the real chip would continue to do that) and it would just be there so the save state system has something to capture from.

Offline nuu

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Re: Save states on SD2Snes
« Reply #62 on: March 02, 2020, 05:13 PM »
You mean it would only be tracking the sound data sent to the APU so that it knows the state of the APU? That sounds like a much better solution, but it's not what I've heard.

Here is the relevant interview part:
Quote from: Ikari
I hope to overcome this limitation by running my own APU implementation on the FPGA which makes me the “owner” of its state too, so I can grab it whenever I want.
The original APU would be silenced by running a little hook on reset that uploads an infinite loop so it doesn’t react to any CPU access. The sd2snes would then override the bus with its own APU responses accordingly.
https://www.retrorgb.com/sd2snes-pro-more-details-from-ikari.html

If it's not made as an optional feature, it's a reprehensible update only useful for certain customers.

Offline WaveRacer

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Re: Save states on SD2Snes
« Reply #63 on: March 02, 2020, 09:31 PM »
Yeah that does sound like the plan is to just bypass using the internal audio altogether. :'( But how would that implementation get the sound from the FPGA through the cartridge slot and out the sound channels?

Offline nuu

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Re: Save states on SD2Snes
« Reply #64 on: March 03, 2020, 12:58 AM »
I suppose audio output is connected to the cartridge connector like on Famicom.