sine-oscillator.s

   1  *
   2  * This is a resonant filter (with infinite? resonance),
   3  * cutoff/oscillation frequency of 50Hz, so that the step value
   4  * will equal 1/8 (IOW, >>3).  The step value is usually:
   5  * (* 2 (sin (* pi (/ 1 frequency)))) - see resonant-filter.lisp
   6  * in my snippets collection.
   7  *
   8  * Actually, this is >>4 now, to make things a bit smoother.
   9  *
  10         section text
  11
  12         global reset_sine_oscillator
  13 reset_sine_oscillator:
  14         MOVE.W #$100, cosine ; Fairly arbitrary max amplitude.
  15         MOVE.W #0, sine
  16         RTS
  17
  18         global step_sine_oscillator
  19 step_sine_oscillator:
  20         MOVE.W sine, D0
  21         ASR.W #4, D0
  22         SUB.W D0, cosine
  23         MOVE.W cosine, D0
  24         ASR.W #4, D0
  25         ADD.W D0, sine
  26         RTS
  27
  28         section data
  29         global sine, cosine
  30 sine:   ds.w 1
  31 cosine: ds.w 1
  32