Teijo Kinnunen
Oksantie 19
FIN-86300  OULAINEN
FINLAND
(FidoNet 2:228/402)     Feb 24 1994



Dear Ray,

I hope the following will help in Mindscapes programers request for a
routine that will help in creating sound effects using the player routine.


Dear Mark, ( and all programers )


As regards producing SFX, OctaMED's synth sound language is a good way to
create them. You can, as requested , program your own routines for changing
the periods/waveforms/volumes of the effects. Whichever way you select,
I've provided a slightly modified version of the OctaMED player routine.
This version has a variable '_freech0'. When you set this variable, the
player immediately stops touching channel 0 registers, so it can be used
for SFX. (You should clear ch 0 DMA after setting this variable ).
When it's cleared, the player continues using channel 0 as usual.

Now, if you want to play synth sounds when channel 0 is unused, the easiest
way is to call the routines in player. _PlayNote triggers a new note, you
need to set some registers (see below) prior to calling it. 'synth_start'
should be called on every player interrupt to update the sound.
You should call these from the player routine itself (e.g. the place after
label 'nonewnote' is good, as long as registers are kept intact, some of
the registers below (A2, A4, A6) are even set for you). The method to
trigger the effects from the game is up to you (e.g. a shared variable might
do the job).

Calling _PlayNote:

registers:
D7 = track number (= 0)
D1 = note number (0 = C-1, 1 = C#1 etc.)
D3 = instrument number (0 - 62)
A2 = address of module
A3 = instrument address in module (mod->song->sample[xx], xx = D3)
A4 = song structure (mod->song)
A5 = track data structure (t03d for track 0)
A6 = data base (DB)

Calling synth_start:

registers:
D0 = trk_synthptr(a5)
A5 = as in _PlayNote

Documentation on using the synth language is provided with OctaMED.

I hope this is of help for those wishing to utilise an SFX channel.

Teijo