freq.asm

.WARMST equ $FF7C
.INCHAR equ $FFcD

EOT equ $04
CR equ $0d
TCTL1 equ $20
TOC2 equ $18
TOC1 equ $16
TFLG1 equ $23
OC1M equ $0C
OC1D equ $0D
    
    ORG $100

    ldx #$1000
    ldd period
    std TOC2,X
    bset TCTL1,X #$40
    
loop:
    ldaa #$40
    bita TFLG1,X
    beq loop

    staa TFLG1,X

    ldd TOC2,X
    addd period
    bvs increment_low
    std TOC2,X
    
    jmp loop

increment_low:
    std TOC2,X
    ldaa t
    inca
    staa t
    cmpa #$01
    beq change_freq
    jmp loop

change_freq:
    ldaa isincrement
    cmpa #$00
    beq inc_freq

dec_freq:
    ldd freq
    subd #$10
    cmpd #$1f4
    bhs save_freq
    std freq
    ldaa #00
    staa isincrement
    jmp change_end

inc_freq:
    ldd freq
    addd #$10
    cmpd #$7d0
    bls save_freq
    std freq
    ldaa #01
    staa isincrement
    jmp change_end

save_freq:    
    std freq
change_end:
    ldx freq
    ldd #$f424
    idiv
    xgdx
    
    aslb 
    rola
    aslb 
    rola
    aslb 
    rola
    aslb 
    rola    
    
    ldx #$1000
    std period
    ldaa #$00
    staa t
    jmp loop

    ;jsr .INCHAR
    ;cmpa #CR
    ;beq end

end:
    jsr .WARMST

t:
    FCB $00 

period:
    FCB $03, $e8  

freq:
    FCB $03, $e8 

isincrement
    FCB $01