C64_SKILLS/.ai/skills/sid-sound/SKILL.md

Skill: SID 6581 Sound Programming

Use this skill when

The task involves music, sound effects, SID registers, waveforms, ADSR envelopes, filters, volume, or paddles.

SID base

SID base: $D400 / 54272.

Each of the three voices uses 7 registers:

Voice	Base decimal	Base hex
Voice 1	54272	$D400
Voice 2	54279	$D407
Voice 3	54286	$D40E

Per voice:

Offset	Purpose
+0	Frequency low
+1	Frequency high
+2	Pulse width low
+3	Pulse width high nybble
+4	Control: gate, sync, ring, test, waveform
+5	Attack/decay
+6	Sustain/release

Global/filter registers:

Decimal	Hex	Purpose
54293	$D415	Filter cutoff low bits
54294	$D416	Filter cutoff high bits
54295	$D417	Resonance/filter voice routing
54296	$D418	Filter mode and master volume
54297	$D419	Paddle X / ADC 1
54298	$D41A	Paddle Y / ADC 2
54299	$D41B	Voice 3 oscillator output
54300	$D41C	Voice 3 envelope output

Waveform bits in control register

Bit/mask	Meaning
$01	Gate
$02	Sync
$04	Ring modulation
$08	Test
$10	Triangle
$20	Sawtooth
$40	Pulse
$80	Noise

Simple BASIC tone

10 S=54272
20 POKE S+24,15:REM VOLUME
30 POKE S+5,9*16+0:REM ATTACK/DECAY
40 POKE S+6,15*16+8:REM SUSTAIN/RELEASE
50 POKE S,37:POKE S+1,17:REM FREQUENCY
60 POKE S+4,17:REM TRIANGLE + GATE
70 FOR T=1 TO 500:NEXT
80 POKE S+4,16:REM GATE OFF

Agent checklist

1. Initialize volume at $D418.
2. Set frequency before opening gate.
3. Set ADSR before gate-on.
4. Clear gate for release.
5. Avoid leaving TEST bit set accidentally.
6. Mention SID 6581 vs 8580 sound differences when relevant.