FANCO v5 — simple sounds, SID versus native SIREN
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SID remains useful because one compact control register selects waveforms,
gate, sync and ring, and two bytes describe an entire ADSR envelope.
Native SIREN is more explicit: it separates waveform selection, modulation,
four envelope segments and mixer routing. That costs more setup bytes but
enables instruments/effects the SID interface cannot describe.

A simple sustained saw near A4, using the SID façade:

.sound on
.org 0x1000
mov.w [0x40], 0x1d44   ; raw SID frequency, approximately 440 Hz
mov.b [0x45], 0       ; short attack/decay
mov.b [0x46], 0xf0    ; full sustain, short release
mov.b [0x44], 0x21    ; saw + gate

The actual v3/v5 assembler emits 25 instruction bytes for these four
stores. This excludes the image header, default CPU-register segment and
any following wait/play loop. .sound on supplies initial master volume.
Turn it off with mov.b [0x44], 0x20. A later note needs only the frequency
word and the waveform/gate byte; keep the envelope settings initialized.

A native saw using generator 3 and an explicit mixer entry:

.sound on
.org 0x1000
mov.w [0x130], 0x8000 ; native musical pitch: A4
mov.b [0x132], 4      ; saw waveform bit
mov.b [0x133], 0x80   ; neutral shape
mov.b [0x137], 255    ; envelope stage 1 target
mov.b [0x139], 255    ; envelope stage 2 target (hold)
mov.b [0x13f], 0x50   ; sustain stage 2 enabled
mov.w [0x200], 0x78a3 ; source 3, gain 1930/4095, centered by default
mov.b [0x134], 1      ; gate on, no modulation

These eight stores emit 50 instruction bytes. Unwritten time/release
fields are zero: native attack/release is immediate, unlike the SID's
short nonzero attack/release. Both examples make a sustained saw; they
are NOT advertised as sample-identical envelopes. Add native time fields
when you want a particular transition. Adjacent fields can be written
with word stores or copied as a reusable 16-byte instrument patch.

After initialization, native note changes likewise need only two stores:

mov.w [0x130], 0x8200 ; B4 (two semitones above A4)
mov.b [0x134], 1      ; preserve source/mode bits if modulation is in use

Turn it off with mov.b [0x134], 0. To retrigger while already held, send
gate off then on; writing the same held gate does not retrigger a note.
Phase restart is independent: bit 3 of word 70 enables hard phase restart
for generator 3. Clear it for legato/free-running oscillator phase.

Mix the interfaces rather than choosing an engine
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You can keep a SID voice's compact frequency/AD/SR writes and add native
phase modulation, self-feedback, stereo pan or a send to shared reverb.
The additional generator need not be in the audible mixer: its envelope
still changes the modulation strength over time. A native CONTROL write
packs gate/source/method, so preserve the gate bit when changing routing.
An old frequency write changes frequency, not the native mixer/effects.
An old waveform/control write DOES intentionally change waveform/gate.

This byte comparison is a manual assembler measurement, not a new test
suite. It supports retaining SID for simple sounds; native configuration
is worth its extra setup when the extra musical controls are needed.
For all raw offsets and combination/shape rules, read SOUND.txt.

Exact native parameter access (added without moving 0100/0200 banks)
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For generators 0–2, native code can use the same raw frequency, 12-bit
pulse width and ADR rates as the factory configuration without writing
0040–005F. Example sustained saw near A4:

.version 5
.sound on
.org 0x1000
mov.w [0x72], 1       ; generator 0: raw PAL frequency format
mov.w [0x74], 1       ; generator 0: independent SID-clocked LFSR
mov.w [0x2fa], 0xf000 ; AD=00, SR=F0; preserves custom segment bank
mov.w [0x100], 0x1d44 ; same exact raw frequency as the SID example
mov.b [0x103], 128    ; neutral native phase shaping after factory seed
mov.b [0x102], 4      ; native saw waveform
mov.b [0x104], 1      ; gate on

The noise-model write is unnecessary for a saw-only instrument, but
keeps the same oscillator/noise behavior if the patch later selects noise.
Subsequent exact pulse updates use 02F4; phase-ring uses native method 6.
These are field-wise inputs to the common generator kernel, not a SID
register forwarding wrapper. Full custom segmented/exponential envelopes
remain available via 0107–010F; writing them selects segmented mode again.

The earlier 25-versus-50-byte example compares two different setup styles,
not equal complete song output. An equal-output comparison must also align
event sample offsets and include all code, lookup tables and music data.
Current audio updates are 48 kHz sample-quantized, not 120 MHz cycle-accurate.