Leprechaun on Carnivore 2 with turboR

Door Manuel

Ascended (18133)

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06-01-2021, 12:36

I'm playing Leprechaun on my CF card with the Carnivore 2 on my turboR. Even though I switch to Z80, the music sounds awful... what could be the issue? Is it the double FM-PAC? (Also one in the C2...)

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Van Manuel

Ascended (18133)

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07-01-2021, 13:33

I made a C2 configuration without FM and after starting that configuration, and the game, the sound is OK. So apparently the game can't handle both internal and external FM-PAC?

Van sdsnatcher73

Prophet (2229)

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07-01-2021, 14:37

Or the FPGA FM is not responding as expected. Either way having 2 FM (FPGA or real) chips does not make sense...

Van Grauw

Ascended (10061)

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07-01-2021, 18:26

The internal and external MSX-MUSIC share the same I/O port. So they both play the same thing. Even with a real OPLL chip this is not ideal but they will function the same so for the most part it will increase the amplitude I think. But since FPGA FM is not perfectly accurate emulation, you will get similar but conflicting output, and I can imagine all kinds of phase cancellation issues.

On a real FM-PAC the output is disabled by default. The official process (from MSX datapack) is to first detect an internal MSX-MUSIC (APRLOPLL signature) and if it’s found just output to the MSX-MUSIC I/O port. If it’s not found, then search for an external FM-PAC (OPLL signature) and set the enable bit before outputting to the I/O port. This ensures that at no time do two MSX-MUSICs sound at the same time.

Of course most MSX-MUSIC cartridges in use today are simplified clones and actually do not implement the enable bit nor the memory-mapped I/O of the FM-PAC (I wish!). So you have to physically unplug them. Also probably not all software implements the above mentioned mechanism properly. If the issue is specific to Leprechaun, maybe that is the case.

Van Manuel

Ascended (18133)

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07-01-2021, 22:42

@sdsnatcher73 True, but it comes by default in Carnivore 2... and I can't remove it from my FS-A1GT either.

@Grauw: so far I have only see it in Leprechaun. So I guess it's an issue in the music routes in Leprechaun. Perhaps also Brisk.

EDIT: hmm, now trying again with the default config, but at 50Hz... no issue anymore!? I guess it was something else after all.