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Nice! The SPC700 has a sleep instruction that waits until a hardware interrupt, but the hardware interrupt pins on the SNES are not connected, so it turns into a "turn off the processor until you power off" command.

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Mechanics Explained

@RetroGameMechEx

A rundown of the instruction set used by the SPC700 that is found in the Super NES's sound system! youtu.be/fEfnvUisAbM

6:22 PM · Apr 14, 2022

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It also has a dedicated "turn off the CPU until until you power off" command, just to be sure.

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Pope of Otterdom

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I assume it was inherited from whatever CPU Sony based it on?

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Yeah. Or they intended to maybe reuse the chip on other machines, which might attach those pins.

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Cero Z Datafile Vol 2

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seems like a wasted opprotunity to not be using maskable interupts for LFOs or something if the pins are there that or having a way to hook them up to an expansion port and do fun stuff with that like turn your snes into a sampler with midi and audio inputs

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I saw SCP 700... and was very worried for a sec.

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For a moment I thought this was related to the SCPs from the other day

Soul Filing Cabinets / Cradle of no / AMA

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Very true.