; Four voices on one tick, staggered so that each can be heard on its own.
;
; M2 of the music player. What is being checked is that the voices share the tick and NOTHING
; ELSE: each keeps its own place in its own track and its own count of how long the note it is
; holding lasts, so one can rest while another plays.
;
; Twelve ticks of 125,000 cycles, which is a sixteenth note at 120 beats a minute:
;
;   ticks 0-3    voice 0 plays middle C          voice 1 rests
;   ticks 4-7    voice 0 rests                   voice 1 plays the C above it
;   ticks 8-11   voice 0 plays middle C          voice 1 plays the C above it
;
; So the first two windows have one voice in them and can be measured for pitch, and the third
; has both and can be measured for level. Two voices sounding at once cannot be asked their
; pitch - a crossing counter given two notes answers with neither.
;
; THIS IS DELIBERATELY NOT Apps/Play.asm. It shares the design and not the code, and it is
; smaller: no track ever ends here, so there is no live flag and no count of what is still
; playing. What it has is the part worth pinning - a cursor and a countdown per voice, moved
; with LDD and STD.
;
; Written by Anachronaut

#Program
start:
  RSTA
  CALL setUpChannel
  INIA 0d1
  CALL setUpChannel

  INIA 0x60
  OUTA 0x46

  ; 125,000 cycles a tick. The period before the control byte, because writing control with
  ; the run bit set is what loads it.
  INIA 0x01
  OUTA 0x52
  INIA 0xE8
  OUTA 0x53
  INIA 0x48
  OUTA 0x54
  INIA 0x07
  OUTA 0x51
  SIF

  SETD.1 Voice0
  SETD.0 Track0
  CALL startVoice
  SETD.1 Voice1
  SETD.0 Track1
  CALL startVoice

  ; Twelve ticks. B survives the calls below, because a CALL saves it.
  INIB 0d12
tickLoop:
  SETD.1 Voice0
  RSTA
  CALL stepVoice
  SETD.1 Voice1
  INIA 0d1
  CALL stepVoice
  DECB
  BRB lastTick
  WAIT
  BRI tickLoop

lastTick:
  ; The twelfth step started a note and nothing has waited for it yet. Without this the last
  ; tick is never rendered, and a window measuring it runs off the end of the samples.
  WAIT

done:
  CIF
  RSTA
  OUTA 0x51
  HALT

; A is the channel and DP1 the voice's four bytes: cursor high, cursor low, count, spare.
; Both survive the CALL that got here.
stepVoice:
  SETD.3 ThisChannel
  STA.3

  DPUP.1 0d2
  LDA.1
  DECA
  STA.1                     ; One tick less of whatever is sounding.
  DPDN.1 0d2
  BNA stepDone

  ; The count ran out. Select the channel first: every sound port writes to whichever channel
  ; was named last, so a voice that forgot would be playing somebody else's part.
  LDA.3
  OUTA 0x41
  RSTA
  OUTA 0x45                 ; Let go of the note that just ended.

  LDD.0.1                   ; DP0 is this voice's place in its track.
  LDA.0
  INCD.0
  LDB.0                     ; How many ticks it lasts.
  INCD.0
  STD.0.1
  DPUP.1 0d2
  STB.1

  ; A is still the note. Zero is a rest: the ticks pass with nothing started.
  BRA stepDone
  OUTA 0x44
stepDone:
  RET

; DP1 a voice, DP0 its track. A count of one, so the first pass fetches the first event.
startVoice:
  STD.0.1
  DPUP.1 0d2
  INIA 0d1
  STA.1
  RET

; Held at full and released quickly, so a note lasts exactly its ticks and the boundary
; between two of them is something a counter can find.
setUpChannel:
  OUTA 0x41
  RSTA
  OUTA 0x42
  INIA 0d2
  OUTA 0x43                 ; Saw
  INIA 0x01
  OUTA 0x42
  INIA 0xFF
  OUTA 0x43
  INIA 0x05
  OUTA 0x42
  INIA 0x01
  OUTA 0x43                 ; Oscillator 0, on and loud.
  INIA 0x20
  OUTA 0x42
  RSTA
  OUTA 0x43                 ; No attack
  INIA 0x21
  OUTA 0x42
  RSTA
  OUTA 0x43                 ; no decay
  INIA 0x22
  OUTA 0x42
  INIA 0xFF
  OUTA 0x43                 ; and held at full.
  INIA 0x23
  OUTA 0x42
  INIA 0d5
  OUTA 0x43
  RET

tick:
  RETI

#Data

Voice0:
  0x00 0x00 0x00 0x00
Voice1:
  0x00 0x00 0x00 0x00
ThisChannel:
  0x00

; Middle C, then out of the way, then back - against the octave above doing the opposite.
Track0:
  0d60 0d4
  0d00 0d4
  0d60 0d4
  0d00 0xFF
Track1:
  0d00 0d4
  0d72 0d4
  0d72 0d4
  0d00 0xFF

#Vectors
  Boot         start
  Device 0x50  tick