tape code cleanup, added impulse detection for normal mode
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@@ -7,17 +7,19 @@
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// We have the following possible CPU frequencies:
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// - C64 PAL: CPU frequency 0.985248 MHz
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// - C64 NTSC: CPU frequency 1.022727 MHz
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// - VIC-20 PAL: CPU frequency 1.108405 MHz
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// - VIC-20 NTSC: CPU frequency 1.022727 MHz
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// Since VIC-20 tapes are not expected to be loaded often, routine will be optimized for C64 timings
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// Average is 1.0039875 MHz and we will take this value for calculation (but it really does not change much).
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//
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// We have to distinguish the following pulse lengths (http://sidpreservation.6581.org/tape-format/):
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// - S (short) 352 us
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// - M (medium) 512 us
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// - L (long) 672 us
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// This gives us the following thresholds (where average CPU frequency is 1.0039875 MHz):
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// - S vs M 432 us (54 8-cycle periods)
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// - M vs L 592 us (74 8-cycle periods)
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//
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// This gives us the following thresholds
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// - S vs M 432 us (108 or $6C 4-tick periods)
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// - M vs L 592 us (149 or $95 4-tick periods)
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//
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// 4-tick periods should be enough - TAP file format description (http://unusedino.de/ec64/technical/formats/tap.html)
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// tells it uses exactly 8 PAL ticks as a resolution
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// The following encoding is used:
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// (S,M) = 0 bit
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@@ -30,7 +32,50 @@
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load_tape_normal:
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STUB_IMPLEMENTATION()
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jsr tape_ditch_verify // only LOAD is supported, no VERIFY
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// Setup CIA #2 timers
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ldx #$03 // set timer A to 4 ticks
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stx CIA2_TIMALO // $DD04
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ldx #$00
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stx CIA2_TIMAHI // $DD05
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stx CIA2_TIMBHI // $DD07
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dex // puts $FF - for running timer B as long as possible
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stx CIA2_TIMBLO // $DD06
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// Let timer A run continuously
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ldx #%00010001 // start timer, force latch reload
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stx CIA2_CRA // $DD0E
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// Start playing
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jsr tape_clean_sid
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jsr tape_ask_play
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// FALLTROUGH
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load_tape_normal_header:
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// XXX replace this placeholder by a real routine
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jsr tape_load_get_pulse
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ldx #$00
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cmp #($100 - $6C - $05)
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bcs !+
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#if CONFIG_COLORS_BRAND && CONFIG_BRAND_ULTIMATE_64
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ldx #$0B
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#else
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ldx #$06
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#endif
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!:
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stx VIC_EXTCOL
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jmp load_tape_normal_header
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#endif
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@@ -98,88 +98,5 @@ load_tape_turbo_loop:
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beq_far tape_load_success
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jmp tape_load_error
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tape_turbo_get_byte:
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lda #$01
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sta ROPRTY // init the to-be-read byte with 1
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!:
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jsr tape_turbo_get_bit
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rol ROPRTY
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bcc !- // is the initial 1 shifted into carry already?
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lda ROPRTY // much nicer than ldx #8: dex: loop
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rts
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tape_turbo_get_bit:
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lda #$10
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!:
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bit CIA1_ICR // $DC0D
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beq !- // busy loop to detect signal
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lda CIA2_ICR // $DD0D
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pha
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lda #$19
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sta CIA2_CRA // $DD0E
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pla
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pha // audio/video effects
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asl
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sta SID_SIGVOL
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beq !+
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#if CONFIG_COLORS_BRAND && CONFIG_BRAND_ULTIMATE_64
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lda #$0B
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#else
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lda #$06
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#endif
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!:
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sta VIC_EXTCOL
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pla
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lsr
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rts
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tape_turbo_sync_common:
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jsr tape_turbo_get_bit
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rol ROPRTY
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lda ROPRTY
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cmp #$02
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bne tape_turbo_sync_common
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rts
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tape_turbo_sync_header:
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ldx #$FF
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!:
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ldy #$03
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!:
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jsr tape_turbo_sync_common
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dey
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bne !-
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dex
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bne !--
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// FALLTROUGH
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tape_turbo_sync_payload:
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jsr tape_turbo_sync_common
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!:
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ldx #$09 // 9,8,... is real turboTape
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!: // I sometimes used 8,7,6... to avoid it being listed in vice :)
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jsr tape_turbo_get_byte
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cmp #$02
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beq !-
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ldy #$00
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!:
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cpx ROPRTY
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bne tape_turbo_sync_payload
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jsr tape_turbo_get_byte
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dex
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bne !-
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rts
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#endif // CONFIG_TAPE_TURBO
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@@ -0,0 +1,42 @@
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//
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// Tape (turbo) helper routine - pulse reading
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//
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// Returns pulse length (with a bias, see comments) in .A
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//
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#if CONFIG_TAPE_NORMAL
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tape_load_get_pulse:
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// Contrary to original ROM implementation we do not use interrupts
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// (see http://unusedino.de/ec64/technical/formats/tap.html) - busy wait
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// implementation is probably just shorter
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lda #$10
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!:
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bit CIA1_ICR // $DC0D
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bne !-
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!:
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bit CIA1_ICR // $DC0D
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beq !- // busy loop to detect signal, restart timer afterwards
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lda CIA2_TIMBLO // $DD06
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ldx #%01010001 // start timer, force latch reload, count timer A underflows
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stx CIA2_CRB // $DD0F
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// Since the signal appeared to the point of timer restart we used:
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// bit - 4 cycles
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// beq - 2 cycles
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// lda - 4 cycles
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// ldx - 2 cycles
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// stx - 4 cycles
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// plus approx. 3 cycles (bit + beq time divided by 2) from value change to 'bit' instruction,
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// this is total 19 cycles, or $5 periods of 4 ticks (timer A) each - we need to take it into account
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// every time we check the pulse length
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rts
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#endif
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@@ -0,0 +1,42 @@
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//
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// Tape (turbo) helper routine - bit reading
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//
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// Based on routine by enthusi/Onslaught, found here:
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// - https://codebase64.pokefinder.org/doku.php?id=base:turbotape_loader_source
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#if CONFIG_TAPE_TURBO
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tape_turbo_get_bit:
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lda #$10
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!:
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bit CIA1_ICR // $DC0D
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beq !- // busy loop to detect signal
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lda CIA2_ICR // $DD0D
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pha
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lda #%00011001 // start timer, one-shot, force latch reload
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sta CIA2_CRA // $DD0E
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pla
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pha // audio/video effects
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asl
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sta SID_SIGVOL
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beq !+
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#if CONFIG_COLORS_BRAND && CONFIG_BRAND_ULTIMATE_64
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lda #$0B
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#else
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lda #$06
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#endif
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!:
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sta VIC_EXTCOL
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pla
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lsr
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rts
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#endif // CONFIG_TAPE_TURBO
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@@ -0,0 +1,26 @@
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//
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// Tape (turbo) helper routine - byte reading
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//
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// Based on routine by enthusi/Onslaught, found here:
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// - https://codebase64.pokefinder.org/doku.php?id=base:turbotape_loader_source
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#if CONFIG_TAPE_TURBO
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tape_turbo_get_byte:
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lda #$01
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sta ROPRTY // init the to-be-read byte with 1 (canary bit to mark loop end)
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!:
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jsr tape_turbo_get_bit
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rol ROPRTY
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bcc !- // is the initial 1 shifted into carry already?
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lda ROPRTY // much nicer than ldx #8: dex: loop
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rts
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#endif // CONFIG_TAPE_TURBO
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@@ -0,0 +1,56 @@
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//
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// Tape (turbo) helper routine - synchronization handling
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//
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// Based on routine by enthusi/Onslaught, found here:
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// - https://codebase64.pokefinder.org/doku.php?id=base:turbotape_loader_source
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#if CONFIG_TAPE_TURBO
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tape_turbo_sync_common:
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jsr tape_turbo_get_bit
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rol ROPRTY
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lda ROPRTY
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cmp #$02
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bne tape_turbo_sync_common
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rts
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tape_turbo_sync_header:
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ldx #$FF
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!:
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ldy #$03
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!:
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jsr tape_turbo_sync_common
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dey
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bne !-
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dex
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bne !--
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// FALLTROUGH
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tape_turbo_sync_payload:
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jsr tape_turbo_sync_common
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!:
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ldx #$09 // 9,8,... is real turboTape
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!: // I sometimes used 8,7,6... to avoid it being listed in vice :)
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jsr tape_turbo_get_byte
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cmp #$02
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beq !-
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ldy #$00
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!:
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cpx ROPRTY
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bne tape_turbo_sync_payload
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jsr tape_turbo_get_byte
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dex
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bne !-
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rts
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#endif // CONFIG_TAPE_TURBO
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