;;; lexicographical duty cycle prefix
;;; by HertzDevil
;;; untested on real music data

; driver.s
var_ch_DutyCycle:       .res SFX_WAVE_CHANS ;; existing
var_ch_LexDuty:         .res SFX_WAVE_CHANS

; player.s, command table
ft_command_table:               ;; existing
    ; ...
    .word ft_cmd_dpcm_pitch     ;; existing
    .word ft_cmd_lex_duty
    ; update the command_t enum in
    ; PatternCompiler.cpp accordingly
    ; with CMD_EFF_LEX_DUTY = 29

; player.s, effect table
ft_cmd_lex_duty:
    jsr ft_get_pattern_byte
    sta var_ch_LexDuty, x
    jmp ft_read_note

; player.s, line 333
    lda var_ch_LexDuty, x
    beq :+++
    cmp #$05
    bcs :+
    ; one frame
    sbc #$00
    jmp @PrepareDuty
:   cmp #$15
    bcs :+
    ; two frames
    sbc #$04
    and #$03
    jmp @PrepareDuty
:   ; three frames
    sbc #$14
    and #$03
    jmp @PrepareDuty
:   lda var_ch_DutyCycle, x     ;; existing
    and #$F0                    ;; existing
    sta var_ch_DutyCycle, x     ;; existing
    lsr a                       ;; existing
    lsr a                       ;; existing
    lsr a                       ;; existing
    lsr a                       ;; existing
    bpl @WriteDuty ; always
@PrepareDuty:
    pha
    lda var_ch_DutyCycle, x
    and #$F0
    sta var_ch_DutyCycle, x
    pla
@WriteDuty:
    ora var_ch_DutyCycle, x     ;; existing
    sta var_ch_DutyCycle, x     ;; existing
    lda var_ch_LexDuty, x
    beq :+++
    cmp #$05
    bcs :+
    lda #$00
    bpl @DoneLexDuty ; always
:   cmp #$15
    bcs :+
    sbc #$04
    lsr a
    lsr a
    sec
    adc #$04
    bpl @DoneLexDuty ; always
:   sbc #$14
    lsr a
    lsr a
    sec
    adc #$14
@DoneLexDuty:
    sta var_ch_LexDuty, x
:
    ; ...