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105 lines
2.4 KiB
ArmAsm
105 lines
2.4 KiB
ArmAsm
; this code was widely shared for playing tones on Apple II
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; by POKEing the machine language and CALLing from BASIC
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; it's originally by Paul Lutus, from the Apple II Red Book p45
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; it's hard to find good info on this, but loading from $C030
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; "toggles" the speaker. So toggling twice is esentially a square wave?
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; using regular load/store/bit of $C030 is safe. Some of the more
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; advanced addressing modes can double-toggle due to how some 6502
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; implementations run the address bus
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; these seem to have been calculated assuming a 1MHz clock
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; but the Apple II actually runs at roughly 1.023MHz
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; or a frequency of 1/(speaker_freq*20.46e-6)
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; to go other way, speaker_freq=1/(freq*20.46e-6)
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; this table of notes was from
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; http://eightbitsoundandfury.ld8.org/programming.html
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; but seems off a bit and also assumes 1MHz clock
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; 1MHz 1.023MHz
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NOTE_C3 = 255 ; G3=5217us = 192Hz (G3, 5218us = 196Hz 249)
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NOTE_CSHARP3 = 241 ; 4931us = 203Hz (G#3, 4931us = 207Hz
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NOTE_D3 = 227 ;
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NOTE_DSHARP3 = 214
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NOTE_E3 = 202
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NOTE_F3 = 191
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NOTE_FSHARP3 = 180
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NOTE_G3 = 170
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NOTE_GSHARP3 = 161
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NOTE_A3 = 152
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NOTE_ASHARP3 = 143
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NOTE_B3 = 135 ; 1350us = 740Hz (F#5)
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NOTE_C4 = 128
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NOTE_CSHARP4 = 121
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NOTE_D4 = 114
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NOTE_DSHARP4 = 108
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NOTE_E4 = 102
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NOTE_F4 = 96
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NOTE_FSHARP4 = 91
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NOTE_G4 = 85
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NOTE_GSHARP4 = 81
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NOTE_A4 = 76
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NOTE_ASHARP4 = 72
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NOTE_B4 = 68
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NOTE_C5 = 64
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NOTE_CSHARP5 = 60
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NOTE_D5 = 57
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NOTE_DSHARP5 = 54
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NOTE_E5 = 51
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NOTE_F5 = 48
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NOTE_FSHARP5 = 45
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NOTE_G5 = 43
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NOTE_GSHARP5 = 40
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NOTE_A5 = 38
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NOTE_ASHARP5 = 36
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NOTE_B5 = 34
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; B5 = 988 Hz, 1021us
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;=====================================================
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; speaker tone
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;=====================================================
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; A,X,Y trashed
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; duration also trashed
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; this was designed by basic to be poked into 770 ($302)
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; on an Applesoft CALL, X=$9d, Y=$02 (A,Y = Address to call)
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; it was originally designed for Integer BASIC where Y=0 on call
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; the inner freq loop is roughly FREQ*10cycles
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; so the square wave generated has a period of
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; freq*20*1.023us
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; or a frequency of 1/(freq*20.46e-6)
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speaker_tone:
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ldy #0 ; 3
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speaker_tone_loop:
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lda $C030 ; click speaker ; 4
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speaker_loop:
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dey ; ; 2
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bne freq_loop ; ; 2/3
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dec speaker_duration ; (Duration) ; 6
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beq done_tone ; 2/3
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freq_loop:
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dex ; 2
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bne speaker_loop ; 2/3
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ldx speaker_frequency ; (Frequency) ; 4
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jmp speaker_tone_loop ; 3
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done_tone:
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rts
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speaker_duration:
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.byte $00
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speaker_frequency:
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.byte $00
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