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add some documentation to the psg module

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Irmen de Jong 2022-08-19 22:17:23 +02:00
parent 6454bf8ec4
commit a878c9a61d
1 changed files with 20 additions and 1 deletions
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21
compiler/res/prog8lib/cx16/psg.p8
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@ -15,6 +15,12 @@ psg {
const ubyte RIGHT = %10000000
sub voice(ubyte voice_num, ubyte channel, ubyte volume, ubyte waveform, ubyte pulsewidth) {
; -- Enables a 'voice' on the PSG.
; voice_num = 0-15, the voice number.
; channel = either LEFT or RIGHT or (LEFT|RIGHT). Specifies the stereo channel(s) to use.
; volume = 0-63, the starting volume for the voice
; waveform = one of PULSE,SAWTOOTH,TRIANGLE,NOISE.
; pulsewidth = 0-63. Specifies the pulse width for waveform=PULSE.
envelope_states[voice_num] = 255
cx16.r0 = $f9c2 + voice_num * 4
cx16.VERA_CTRL = 0
@ -30,12 +36,15 @@ psg {
; sub freq_hz(ubyte voice_num, float hertz) {
; ; this would rely on floating point math to convert hertz to vera frequency
; ; TODO should be replaced by integer math maybe with a lookup table?
; ; could be replaced by integer math maybe with a lookup table?
; uword vera_freq = (hertz / 0.3725290298461914) as uword
; freq(voice_num, vera_freq)
; }
sub freq(ubyte voice_num, uword vera_freq) {
; -- Changes the frequency of the voice's sound.
; voice_num = 0-15, vera_freq = 0-65535 calculate this via the formula given in the Vera's PSG documentation.
; (https://github.com/commanderx16/x16-docs/blob/master/VERA%20Programmer's%20Reference.md)
cx16.r0 = $f9c0 + voice_num * 4
cx16.VERA_CTRL = 0
cx16.VERA_ADDR_L = lsb(cx16.r0)
@ -47,6 +56,8 @@ psg {
}
sub volume(ubyte voice_num, ubyte vol) {
; -- Modifies the volume of this voice.
; voice_num = 0-15, vol = 0-63 where 0=silent, 63=loudest.
cx16.r0 = $f9c2 + voice_num * 4
cx16.vpoke(1, cx16.r0, cx16.vpeek(1, cx16.r0) & %11000000 | vol)
envelope_volumes[voice_num] = mkword(vol, 0)
@ -54,11 +65,18 @@ psg {
}
sub pulse_width(ubyte voice_num, ubyte pw) {
; -- Modifies the pulse width of this voice (when waveform=PULSE)
; voice_num = 0-15, pw = 0-63 where 0=narrow, 63=50%cycle so square wave.
cx16.r0 = $f9c3 + voice_num * 4
cx16.vpoke(1, cx16.r0, cx16.vpeek(1, cx16.r0) & %11000000 | pw)
}
sub envelope(ubyte voice_num, ubyte maxvolume, ubyte attack, ubyte sustain, ubyte release) {
; -- Enables AttackSustainRelease volume envelope for a voice.
; Note: this requires setting up envelopes_irq() as well, read its description.
; voice_num = 0-15 maxvolume = 0-63
; attack, sustain, release = 0-255 that determine the speed of the A/D/R.
; TODO describe how the speeds are calculated. For now, experiment. Higher values means *slower* enveloping.
envelope_states[voice_num] = 255
envelope_attacks[voice_num] = attack
envelope_sustains[voice_num] = sustain
@ -73,6 +91,7 @@ psg {
}
sub silent() {
; -- Shut down all PSG voices.
for cx16.r1L in 0 to 15 {
envelope_states[cx16.r1L] = 255
envelope_volumes[cx16.r1L] = 0