AnachronautandClaude Opus 5
79d1e2639b
Play is the scheduler: one tick, four cursors. Every voice keeps its own place in its own track and its own count of how much longer the note it is holding lasts, so a voice playing whole notes and a voice playing eighths cost the same and never have to know about each other. They share the tick and nothing else. That is what makes the tick the smallest subdivision in the piece rather than a note length - it is the only unit four parts can agree on. A track is pairs of bytes: what to play, then how many ticks it lasts. MIDI notes stop at 127, so the top of the byte was free and neither the rest nor the end marker had to be invented - 0 is a rest and 0xFF ends the track. Examples/tune.asm spent zero on its end marker and so could not write a rest at all, which one voice can live with and four cannot: the silences are what make them separate parts rather than a chord. The state is four bytes a voice, cursor first because that is what LDD and STD move - a pointer through a pointer, which is what lets this be a loop over four voices instead of the same code four times. CALL preserves A and DP0-2, so a caller says which voice it means in two instructions. The piece is four bars of C, F, G, C with the parts moving at four different rates, because that is the thing one channel cannot do. All four channels get the same instrument, which is exactly what M3 replaces. fourVoiceTest staggers two voices so each gets a stretch alone: middle C while the other rests, the octave while the first is silent, then both. The first two are measured for pitch and the third for level, because TWO NOTES CANNOT BE ASKED THEIR PITCH - the crossing counter adds them and answers 785 hertz, which is 262 plus 523 and a fact about nothing. Verified with break.sh: dropping the channel select trips one check, pointing both voices at one cursor trips three. It shares Play's design and not its code, and is smaller - no track ends in it, so there is no live flag and no count of what is still playing. Play.sbx on the disk is why ten recordings moved: one added line each, and the file count with it. Nothing else in them changed. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
182 lines
4.0 KiB
NASM
182 lines
4.0 KiB
NASM
; Four voices on one tick, staggered so that each can be heard on its own.
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;
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; M2 of the music player. What is being checked is that the voices share the tick and NOTHING
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; ELSE: each keeps its own place in its own track and its own count of how long the note it is
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; holding lasts, so one can rest while another plays.
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;
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; Twelve ticks of 125,000 cycles, which is a sixteenth note at 120 beats a minute:
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;
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; ticks 0-3 voice 0 plays middle C voice 1 rests
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; ticks 4-7 voice 0 rests voice 1 plays the C above it
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; ticks 8-11 voice 0 plays middle C voice 1 plays the C above it
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;
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; So the first two windows have one voice in them and can be measured for pitch, and the third
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; has both and can be measured for level. Two voices sounding at once cannot be asked their
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; pitch - a crossing counter given two notes answers with neither.
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;
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; THIS IS DELIBERATELY NOT Apps/Play.asm. It shares the design and not the code, and it is
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; smaller: no track ever ends here, so there is no live flag and no count of what is still
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; playing. What it has is the part worth pinning - a cursor and a countdown per voice, moved
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; with LDD and STD.
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;
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; Written by Anachronaut
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#Program
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start:
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RSTA
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CALL setUpChannel
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INIA 0d1
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CALL setUpChannel
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INIA 0x60
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OUTA 0x46
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; 125,000 cycles a tick. The period before the control byte, because writing control with
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; the run bit set is what loads it.
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INIA 0x01
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OUTA 0x52
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INIA 0xE8
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OUTA 0x53
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INIA 0x48
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OUTA 0x54
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INIA 0x07
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OUTA 0x51
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SIF
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SETD.1 Voice0
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SETD.0 Track0
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CALL startVoice
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SETD.1 Voice1
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SETD.0 Track1
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CALL startVoice
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; Twelve ticks. B survives the calls below, because a CALL saves it.
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INIB 0d12
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tickLoop:
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SETD.1 Voice0
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RSTA
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CALL stepVoice
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SETD.1 Voice1
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INIA 0d1
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CALL stepVoice
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DECB
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BRB lastTick
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WAIT
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BRI tickLoop
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lastTick:
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; The twelfth step started a note and nothing has waited for it yet. Without this the last
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; tick is never rendered, and a window measuring it runs off the end of the samples.
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WAIT
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done:
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CIF
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RSTA
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OUTA 0x51
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HALT
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; A is the channel and DP1 the voice's four bytes: cursor high, cursor low, count, spare.
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; Both survive the CALL that got here.
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stepVoice:
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SETD.3 ThisChannel
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STA.3
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DPUP.1 0d2
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LDA.1
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DECA
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STA.1 ; One tick less of whatever is sounding.
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DPDN.1 0d2
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BNA stepDone
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; The count ran out. Select the channel first: every sound port writes to whichever channel
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; was named last, so a voice that forgot would be playing somebody else's part.
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LDA.3
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OUTA 0x41
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RSTA
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OUTA 0x45 ; Let go of the note that just ended.
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LDD.0.1 ; DP0 is this voice's place in its track.
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LDA.0
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INCD.0
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LDB.0 ; How many ticks it lasts.
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INCD.0
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STD.0.1
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DPUP.1 0d2
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STB.1
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; A is still the note. Zero is a rest: the ticks pass with nothing started.
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BRA stepDone
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OUTA 0x44
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stepDone:
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RET
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; DP1 a voice, DP0 its track. A count of one, so the first pass fetches the first event.
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startVoice:
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STD.0.1
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DPUP.1 0d2
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INIA 0d1
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STA.1
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RET
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; Held at full and released quickly, so a note lasts exactly its ticks and the boundary
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; between two of them is something a counter can find.
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setUpChannel:
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OUTA 0x41
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RSTA
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OUTA 0x42
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INIA 0d2
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OUTA 0x43 ; Saw
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INIA 0x01
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OUTA 0x42
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INIA 0xFF
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OUTA 0x43
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INIA 0x05
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OUTA 0x42
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INIA 0x01
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OUTA 0x43 ; Oscillator 0, on and loud.
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INIA 0x20
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OUTA 0x42
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RSTA
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OUTA 0x43 ; No attack
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INIA 0x21
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OUTA 0x42
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RSTA
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OUTA 0x43 ; no decay
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INIA 0x22
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OUTA 0x42
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INIA 0xFF
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OUTA 0x43 ; and held at full.
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INIA 0x23
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OUTA 0x42
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INIA 0d5
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OUTA 0x43
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RET
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tick:
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RETI
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#Data
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Voice0:
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0x00 0x00 0x00 0x00
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Voice1:
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0x00 0x00 0x00 0x00
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ThisChannel:
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0x00
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; Middle C, then out of the way, then back - against the octave above doing the opposite.
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Track0:
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0d60 0d4
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0d00 0d4
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0d60 0d4
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0d00 0xFF
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Track1:
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0d00 0d4
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0d72 0d4
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0d72 0d4
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0d00 0xFF
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#Vectors
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Boot start
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Device 0x50 tick
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