RetroArch support for SM about archipelago

[Ijwu]

@Berserker66 let me know we never officially supported RA, but I think it is still worth looking into RetroArch compatibility for SM.

[strotlog]

It's a little more complicated than that. But the really simple part is: the old location and the new location from PR #340 are both in the ROM anyway, so that made no difference. (Edit: for deep technical reasons that I can explain if you like, the PR actually should help "non-working" versions of RA like 1.10.0 become "working, but with caveats"!)

Now, to address fully supporting RetroArch, which is not affected by the above change:

RetroArch is able to read the ROM if both of the following conditions are met:

• Using RetroArch <= 1.9.0 or RetroArch >= 1.10.1; AND,
• Using a bsnes-mercury core (such as bsnes-mercury-performance)

Thus RetroArch has sort of always been supported! I would like to write up some instructions to use it, or someone else can.

The dependency on bsnes-mercury isn't the greatest since it's somewhat awkward to manage cores in RetroArch. bsnes-mercury is also pretty finicky about enabling custom MSU music support for the players that want that. There are at least a few ways to go about removing the dependency on bsnes-mercury:

• In RA: Add support in cores other than bsnes-mercury, such as the RA snes9x-current core, for RA's SET_MEMORY_MAPS API. This enables ROM reads. It's a little bit scary to me because you just pass to RA a read/write buffer pointer with no lifetime specified and no notification when RA writes the buffer owned by the emulator core. jsd1982 was thinking about trying this. OR,
• In AP SM ROM: Copy ROM data to a known location in WRAM or SRAM, first ensuring that no one else wants to write to the chosen location. OR,
• In AP SM ROM: Add a command to the multiworld communication library which enables the ROM's code to accept a read request for a particular address from SNIClient, and read and return ROM data to the SNIClient.

[strotlog]

[MW] never officially supported RA

I suppose I should ask @Berserker66 - beyond some of the technical stuff I described in the above comment, is there any reason RetroArch support couldn't be made official?

[lordlou]

I concur with strotlog: SM_ROMNAME_START was never in RAM to start with. I missed that.

[Berserker66]

@strotlog
It simply never worked and nobody ever reported it. RA cannot read ROM, only RAM.
But your PR has now made us aware of this.

[strotlog]

OK, neat.

Just to reiterate, RA can read ROM data when the user selects a RA core that implement RA's SET_MEMORY_MAPS API. bsnes-mercury is the only such SNES core that I'm aware of.

Archipelago does support SM in RetroArch today; the biggest limitation is documentation!

Maybe the perception of it not working comes from a previous bug: For a certain period of time (RA 1.92 thru 1.10.0), RA had a problem with the correctness of where it read from within the ROM, when a client requested an address in non-contiguous ROM address space. (99% of the SM ROM is mapped non-contiguously with the beginning of the ROM.) But I tracked that bug down and got it fixed with RA folks in RA 1.10.1.

[Ijwu]

According to #365 this seems solved for. Thank you for your contributions, in knowledge and docs, @strotlog. I am closing this issue now.