How to create SFX for Moonsound's FM registers ?

Thank a lot for all the helpful tips.

So to summarize:

1. Hex edit Moonblaster 1.4 to playback on 60fps.
2. Create sfx in MoonBlaster 1.4 or MoonBlaster FM.
3. Convert the sfx to VGM format (this is done how exactly ? A conversion script in OpenMsx ?)
4. Playback the VGM datastream in game. (VGMPlay 1.3 ? http://www.grauw.nl/projects/vgmplay-msx/) ?

Is this correct ?

I would stick to MoonBlaster 1.4 for simplicity unless you really need 4-op voices or the extra waveforms.

The vgm_rec function is built-in to openMSX. Type help vgm_rec for usage info.

I think using VGMPlay and the VGM format directly is overkill, VGMPlay would also be complicated to integrate.

VGM is a quite simple data format that essentially consists of a stream of commands like “set sound chip X register Y to value Z” mixed with “wait N time”. You can make a script to convert it to an even simpler format specific for sound effects in your game that consists of “register, value”, “wait 1 interrupt” and “end of effect” commands.

A playback routine can then be as simple as:

; hl = effect commands
SFX_Play:
    ld (SFX_pointer),hl    ; set effect stream to start playing
    ret

SFX_InterruptHandler:
    ld hl,(SFX_pointer)    ; get current command pointer
    call SFX_NextCommand   ; process commands
    ld (SFX_pointer),hl    ; store new command pointer
    ret                    ; return from interrupt

; hl = command pointer
SFX_NextCommand:
    ld a,(hl)              ; get command byte
    inc hl                 ; move pointer to next byte
    cp 0FEH                ; check command byte value
    jr c,SFX_WriteCommand  ; 00-FD: write command (register, value pair)
    jr z,SFX_EndCommand    ;    FE: end command
    ret                    ;    FF: wait 1 interrupt (return until next interrupt)

; a = register number
; hl = command pointer
SFX_WriteCommand:
    out (0C4H),a           ; output register number to OPL4
    ld a,(hl)              ; get value byte
    inc hl                 ; move pointer to next byte
    out (0C5H),a           ; output register value to OPL4
    jr SFX_NextCommand     ; process the next command

; hl = command pointer
SFX_EndCommand:
    dec hl                 ; just stay on the end command
    ret                    ; next interrupt it will get the end command again, and again

SFX_pointer:
    dw SFX_dummyEffect     ; command pointer, initially pointing to a dummy effect

SFX_dummyEffect:
    db 0FEH                ; dummy effect consisting of only end command

Thanks again for all the tips and examples. Much appreciated.

@grauw on a sidenote.

For a OPL4 music track that uses 24 channels.
Playback with the Moonblaster replayer would be extremely slow and to save cpu cycles it might be an idea to use VGMPlay to play the music.
Do you think this is a feasible option in a game environment?

Is it doable to have (the core of) VGMPlay run in a game ?
And how would you deal with the playback of songs that are let's say >50kb ?

I wanna try to stream music that I record in Openmsx with vgm_rec

@Grauw

I just did a few tests recording in MBWave.
I recorded in Openmsx like so:
vgm_rec start Moonsound
And I stopped 10 seconds later like this:
vgm_rec stop
Filesize was 700kb.
Tried several times, every time huge files for a song that uses no more than 4 channels, playback time just a few seconds.

How is this done ?

Hey norakomi,

The VGM tools are command line applications, you can find them here:

https://vgmrips.net/forum/viewtopic.php?t=207

Check the Readme.txt for information about vgm_facc and vgm_cmp. (I misremembered the name vgm_opt, you’ll want to use vgm_cmp instead.)

After these optimisations you can probably expect to reduce the size by about an additional 50% to ⅔rd by converting it to a custom format.