; The timer interrupting, which is what a music routine actually wants.
;
; 125,000 cycles is a sixteenth note at 120 beats a minute. THE SCREEN CANNOT EXPRESS IT: a
; frame is 16,667 cycles, so that beat is seven and a half of them, and a program timing music
; on frames has to pick a tempo whose subdivisions happen to land on whole ones.
;
; Eight of them is a second, and what is recorded is that it took one - and that the machine
; slept through nearly all of it, which is the difference between waiting for a beat and
; counting up to it.
;
; Written by Anachronaut

#Program
start:
  ; 125,000 cycles: a sixteenth note at 120 beats a minute, which the screen's frame
  ; cannot express at all.
  INIA 0x01
  OUTA 0x52
  INIA 0xE8
  OUTA 0x53
  INIA 0x48
  OUTA 0x54                 ; 0x01E848 = 125,000

  INIA 0x07
  OUTA 0x51                 ; Run, repeat, interrupt.
  SIF

  INIB 0d8
everyBeat:
  WAIT
  INIA 0d46
  OUTA 0x00
  DECB
  BNB everyBeat

  CIF
  RSTA
  OUTA 0x51
  INIA 0d10
  OUTA 0x00
  HALT

beat:
  RETI

#Vectors
  Boot start
  Device 0x50  beat