119 lines
1.8 KiB
ArmAsm
119 lines
1.8 KiB
ArmAsm
#if ROM_LAYOUT_STD || (ROM_LAYOUT_M65 && SEGMENT_KERNAL_0)
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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_header:
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#if CONFIG_TAPE_TURBO_AUTOCALIBRATE
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// Initial pulse threshold
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lda #$BF // auto-calibration under VICE often returns this value
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sta IRQTMP+0
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// Zero temporary stack area
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lda #$00
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ldy #$03
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!:
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sta STACK, y
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dey
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bpl !-
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#endif // CONFIG_TAPE_TURBO_AUTOCALIBRATE
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// Synchronize with start of sync sequence
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jsr tape_turbo_sync_first
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// Perform synchronization
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ldx #$C0
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!:
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phx_trash_a
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ldy #$04
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!:
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jsr tape_turbo_get_byte
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cmp #$02
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bne tape_turbo_sync_header // branch if failure
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dey
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bne !-
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plx_trash_a
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dex
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bne !--
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// FALLTROUGH
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#if CONFIG_TAPE_TURBO_AUTOCALIBRATE
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tape_turbo_sync_calibrate:
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ldy #$80
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// FALLTROUGH
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tape_turbo_sync_calibrate_loop:
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// Skip 5 bits
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phy_trash_a
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ldy #$04
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!:
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jsr tape_turbo_get_bit
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bcs tape_turbo_sync_header
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dey
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bpl !-
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jsr tape_turbo_sync_measure_0
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jsr tape_turbo_sync_measure_1
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jsr tape_turbo_sync_measure_0
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ply_trash_a
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dey
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bne tape_turbo_sync_calibrate_loop
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// Calculate new pulse threshold as arithmetic mean
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// We accumulated 256 zeros and 128 ones, so calculating average value is easy
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lda STACK+0
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clc
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ror
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clc
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adc STACK+1
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sta IRQTMP+0
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// FALLTROUGH
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#endif // CONFIG_TAPE_TURBO_AUTOCALIBRATE
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tape_turbo_sync_payload:
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jsr tape_turbo_sync_first
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!:
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ldx #$09 // 9, 8, ...
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!:
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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 INBIT
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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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#endif // ROM layout
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