AnachronautandClaude Opus 5
1687422619
There is no assembler bug. I reported one and was wrong. A label written in the Data Segment does come out as its address, two bytes, most significant first - implemented in populateOutputBuffers, documented in the Assembler Manual, and correct. What misled me was the test I checked it with: the label was the first thing in an unbased Data Segment, so its address really was 0x0000, and I read the right answer as an unfilled placeholder. So Play was doing at run time what the assembler had already offered to do at assembly time. The voice records now carry their track labels directly, which is exactly the shape LDD reads, and nothing relocates on this machine so the address written is the address it will have. That takes out startVoice, its four call sites, and the eight SETDs that fed them: 450 bytes to 379, and the initial state of a voice is now something you can read rather than something you have to follow the code to work out. The comment claiming otherwise is gone from Play.asm, and the same change is made in fourVoiceTest. The music is unchanged - bar by bar the render matches to within one per cent, which is the program loading a shade sooner because it is smaller. Ten recordings moved for the same reason: 446 to 379, and nothing else. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
301 lines
8.5 KiB
NASM
301 lines
8.5 KiB
NASM
; Play.asm
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; Four voices on one clock, which is what music is and one channel cannot be.
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; Written by Anachronaut
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;
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; ---- One tick, four cursors ----
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;
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; The sound device has four channels and no idea when. The timer has a period and no idea
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; what. This is the thing between them: on every tick it walks four voices, and each voice
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; counts down the note it is holding and reads the next one when the count runs out.
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;
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; THE VOICES SHARE NOTHING BUT THE TICK. Each keeps its own place in its own track and its
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; own count of how much longer the current note lasts, so a voice playing whole notes and a
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; voice playing eighths cost the same and never have to know about each other. That is why
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; the tick is the smallest subdivision in the piece rather than a note length: it is the
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; only unit all four can agree on.
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;
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; ---- What a track is ----
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;
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; Pairs of bytes: what to play, then how many ticks it lasts.
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;
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; 0x01 to 0x7F a MIDI note. 60 is middle C and every 12 is an octave.
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; 0x00 a rest - the ticks pass with nothing sounding
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; 0xFF the track is over
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;
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; MIDI notes only reach 127, so the top of the byte was free and neither of those two had to
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; be invented. Examples/tune.asm spent zero on its end marker and so had no way to write a
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; rest at all, which one voice can just about live with and four cannot: voices do not all
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; play at once, and the silences are what makes them separate parts rather than a chord.
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;
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; A note's duration is its whole life. The gate goes down when the count runs out and the
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; next event begins on the same tick, so a gap between two notes is WRITTEN, as a rest,
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; rather than invented by the player out of some fraction it decided on.
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;
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; ---- Where the state lives ----
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;
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; Four bytes a voice: two of cursor, one of count, one of live. The cursor is two bytes and
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; first because that is what LDD and STD move - a pointer through a pointer, which is the
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; whole reason this can be a loop over four voices instead of the same code written out four
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; times.
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#Include services.asm
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#Program
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#Base 0x5000
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start:
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; ---- A sound to play it with ----
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;
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; The same on all four channels, which is exactly what M3 replaces: a patch per voice, out
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; of the format SoundPatch already writes. Until then they are four of the same instrument,
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; which is enough to hear four parts and not enough to enjoy them.
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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 0d2
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CALL setUpChannel
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INIA 0d3
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CALL setUpChannel
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INIA 0x60 ; Room over the top for four voices at once.
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OUTA 0x46
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; ---- The beat ----
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;
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; 125,000 cycles is a sixteenth note at 120 beats a minute, which is the smallest thing
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; this piece divides a beat into. The period goes in before the control byte, because
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; writing control with 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 ; Run, repeat, interrupt.
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SIF
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; ---- The loop ----
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;
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; Step every voice, see whether any of them is still going, and then sleep. Stepping before
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; waiting is what makes the first note sound on the first tick rather than the second.
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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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SETD.1 Voice2
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INIA 0d2
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CALL stepVoice
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SETD.1 Voice3
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INIA 0d3
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CALL stepVoice
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SETD.1 Playing
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LDA.1
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BRA finished
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WAIT ; Nothing at all until the timer says a tick has gone by.
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BRI tickLoop
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finished:
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; Let the last note ring rather than cutting it off, then give the timer back - stopped
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; before the handler goes away, because an interrupt with nothing to catch it is a fault.
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INIB 0d8
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lastRing:
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WAIT
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DECB
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BNB lastRing
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CIF
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RSTA
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OUTA 0x51
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SWI osExit
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; ---- One voice, one tick ----
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;
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; A is the channel and DP1 is the voice's four bytes. Both survive the CALL that got here,
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; which is what lets the caller say which voice it means in two instructions.
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stepVoice:
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SETD.3 ThisChannel
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STA.3 ; A is wanted for other things between here and using it.
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DPUP.1 0d3
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LDA.1 ; Live?
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DPDN.1 0d3
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BRA stepDone
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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 ; Still holding it.
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; ---- The count ran out, so this is a boundary ----
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;
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; Select the channel FIRST. Every sound port below writes to whichever channel was last
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; named, so a voice that forgot would be playing somebody else's part.
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LDA.3 ; DP3 has held the channel since the top of this routine.
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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 now this voice's place in its track.
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LDA.0
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INIB 0xFF
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XOR ; XOR answers in Q and leaves A holding the note.
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BRQ stepEnded
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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 ; The cursor, moved past this event.
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DPUP.1 0d2
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STB.1 ; And the count it will be held for.
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; A is still the note. Zero is a rest, which is a duration with nothing started.
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BRA stepDone
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OUTA 0x44 ; Writing the note is what starts it.
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stepDone:
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RET
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stepEnded:
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; The gate is already down, so the last note is fading. Mark the voice finished and say so.
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DPUP.1 0d3
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RSTA
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STA.1
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SETD.3 Playing
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LDA.3
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DECA
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STA.3
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RET
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; A plucked sound, on the channel named by A.
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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 ; A saw, which has harmonics enough to hear a filter on.
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INIA 0x01
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OUTA 0x42
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INIA 0xFF
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OUTA 0x43 ; Oscillator 0 at full gain
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INIA 0x05
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OUTA 0x42
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INIA 0x01
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OUTA 0x43 ; and switched on, which is a separate write and the one that
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; matters: a gain on an oscillator that is off does nothing.
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INIA 0x20
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OUTA 0x42
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INIA 0d8
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OUTA 0x43 ; Almost no attack
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INIA 0x21
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OUTA 0x42
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INIA 0d140
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OUTA 0x43 ; a long decay
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INIA 0x22
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OUTA 0x42
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INIA 0d60
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OUTA 0x43 ; held quietly rather than at nothing, so a long note is still
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; there when the next one starts
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INIA 0x23
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OUTA 0x42
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INIA 0d40
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OUTA 0x43 ; and a short release when the gate drops.
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RET
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; The tick has nothing to do: the loop above is the player and WAIT only needs something to
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; have happened. A handler still has to exist, because an interrupt with nothing installed to
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; catch it is a fault. Taking it is what brings the line down - a program that POLLED the
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; timer would have to read 0x50 instead.
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tick:
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RETI
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#Data
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#Base 0x3000
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; Four bytes a voice: cursor high, cursor low, count, live.
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;
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; A LABEL WRITTEN HERE COMES OUT AS ITS ADDRESS, two bytes, most significant first - which is
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; exactly the shape LDD reads. So a voice starts pointed at its track without a line of code:
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; nothing relocates on this machine, so the address the assembler wrote is the address it
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; will have.
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;
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; The count starts at one rather than zero so that the first pass through the loop runs it out
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; and fetches the first event. Nothing has to be special-cased for the beginning, and the
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; piece starts on the tick rather than one after it.
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Voice0:
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Track0 0d1 0d1
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Voice1:
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Track1 0d1 0d1
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Voice2:
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Track2 0d1 0d1
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Voice3:
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Track3 0d1 0d1
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Playing:
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0d4
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ThisChannel:
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0x00
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; ---- Four bars of C, F, G, C ----
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;
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; A bar is sixteen ticks. The parts move at four different rates on purpose: this is the
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; thing one channel cannot do, so it is the thing worth playing.
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; The melody, in quarters and halves.
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Track0:
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0d64 0d4 ; E
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0d67 0d4 ; G
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0d72 0d8 ; C, held
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0d65 0d4 ; F
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0d69 0d4 ; A
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0d72 0d8 ; C
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0d62 0d4 ; D
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0d67 0d4 ; G
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0d71 0d8 ; B
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0d72 0d16 ; and home
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0xFF
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; A second part underneath it, in halves.
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Track1:
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0d60 0d8 ; C
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0d64 0d8 ; E
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0d57 0d8 ; A
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0d60 0d8 ; C
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0d59 0d8 ; B
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0d62 0d8 ; D
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0d64 0d16 ; E
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0xFF
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; The bass, one note to a bar.
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Track2:
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0d48 0d16 ; C
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0d41 0d16 ; F
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0d43 0d16 ; G
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0d48 0d16 ; C
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0xFF
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; And an arpeggio in eighths, which is the part that proves the others are not waiting for it.
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Track3:
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0d72 0d2 0d76 0d2 0d79 0d2 0d76 0d2
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0d72 0d2 0d76 0d2 0d79 0d2 0d76 0d2
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0d77 0d2 0d81 0d2 0d84 0d2 0d81 0d2
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0d77 0d2 0d81 0d2 0d84 0d2 0d81 0d2
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0d79 0d2 0d83 0d2 0d86 0d2 0d83 0d2
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0d79 0d2 0d83 0d2 0d86 0d2 0d83 0d2
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0d00 0d16 ; and out, so the last bar is the other three
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0xFF
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#Vectors
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Boot start
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Device 0x50 tick
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