106 lines
2.7 KiB
ArmAsm
106 lines
2.7 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 ; G#3 4931us = 203Hz (G#3, 4931us = 207Hz
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NOTE_D3 = 227 ; A3
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NOTE_DSHARP3 = 214 ; A#3
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NOTE_E3 = 202 ; B3
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NOTE_F3 = 191 ; C4
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NOTE_FSHARP3 = 180 ; C#4
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NOTE_G3 = 170 ; D4
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NOTE_GSHARP3 = 161 ; D#4
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NOTE_A3 = 152 ; E3
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NOTE_ASHARP3 = 143 ; F3
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NOTE_B3 = 135 ; F#3
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NOTE_C4 = 128 ; G
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NOTE_CSHARP4 = 121 ; G#
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NOTE_D4 = 114 ; A
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NOTE_DSHARP4 = 108 ; A#
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NOTE_E4 = 102 ; B3
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NOTE_F4 = 96 ; C
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NOTE_FSHARP4 = 91 ; C#
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NOTE_G4 = 85 ; D
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NOTE_GSHARP4 = 81 ; D#
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NOTE_A4 = 76 ; E
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NOTE_ASHARP4 = 72 ; F
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NOTE_B4 = 68 ; F#
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NOTE_C5 = 64 ; G
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NOTE_CSHARP5 = 60 ; G#
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NOTE_D5 = 57 ; A
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NOTE_DSHARP5 = 54 ; A#
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NOTE_E5 = 51 ; B3
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NOTE_F5 = 48 ; C
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NOTE_FSHARP5 = 45 ; C#
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NOTE_G5 = 43 ; D
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NOTE_GSHARP5 = 40 ; D#
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NOTE_A5 = 38 ; E
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NOTE_ASHARP5 = 36 ; F
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NOTE_B5 = 34 ; F#
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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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; and it was poked to $00 (zero page)
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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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; more exactly, it is (4+10F)+(13+10F) = 20F+17
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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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