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SPC700/Driver Upload
From SnesLab
In order to use main audio (Blargg's trick notwithstanding), the 5A22 must first upload a sound driver to the SPC700 over the following four ports:
| Official Port Name | Port Name (SPC side) | Port Address (SPC side) | Port Name (5A22 side) | Port Address (5A22 side) | Data |
|---|---|---|---|---|---|
| PORT0 | CPUIO0 | 00F4h | APUIO0 | 2140h | The SPC IPL writes AAh here when ready, kick and kickback (as described by fullsnes) also go through here |
| PORT1 | CPUIO1 | 00F5h | APUIO1 | 2141h | The SPC IPL writes BBh here when ready, the 5A22 writes which command ("transfer" or "entry" as described by fullsnes) it wants the IPL to run here, and the driver data is uploaded through here too |
| PORT2 | CPUIO2 | 00F6h | APUIO2 | 2142h | The 5A22 writes the low byte of the upload destination ARAM address here, and the low byte of the entrypoint into the SPC program once all blocks have been uploaded |
| PORT3 | CPUIO3 | 00F7h | APUIO3 | 2143h | The 5A22 writes the high byte of the upload destination ARAM address here, and the high byte of the entrypoint into the SPC program once all blocks have been uploaded. |
The official Super Nintendo development manual describes the driver upload process in Appendix D of Book I. Fullsnes has pseudocode for the upload procedure in https://problemkaputt.de/fullsnes.htm#snesapumaincpucommunicationport, and anomie's SPC700 Doc also lists a very similar 11 step procedure.