working irl decoding
This commit is contained in:
Joppe Blondel
@@ -95,6 +95,11 @@ sample_pulse:
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; returns a (average)
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; cary is timeout
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; uses b,e,h
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; NOTE: USES 8 BIT COUNTER
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; @1MHZ t_long<1.14ms
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; @2MHZ t_long<571us
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; @4MHZ t_long<285us
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; TODO: Check feasibility of using 16bit accumulator
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; -------------------------------------------------------
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average8:
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ld e,0
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@@ -118,27 +123,33 @@ average8:
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ret
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; -------------------------------------------------------
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; Make a +/-25% window around a
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; needs a
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; returns b (minimum) c (maximum)
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; uses e,h
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; NOTE: USES 8 BIT COUNTER
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; @1MHZ t_long<1.14ms
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; @2MHZ t_long<571us
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; @4MHZ t_long<285us
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; TODO: Check feasibility of using 16bit accumulator
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; Make non-overlapping short and long pulse windows
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; Boundary is the midpoint between both averages
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; Short minimum and long maximum allow a 50% margin
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; needs SHORT_AVG and LONG_AVG
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; uses a,c
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; -------------------------------------------------------
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make_window:
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ld e,a
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make_windows:
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ld a,(SHORT_AVG)
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srl a
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srl a
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ld h,a ; h = a/4
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ld a,e
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sub h
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ld b,a ; b = a-25%
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ld a,e
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add h
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ld c,a ; c = a+25%
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ld (SHORT_MIN),a ; short minimum = 50% of short
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ld a,(LONG_AVG)
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ld c,a
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inc a
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srl a ; ceil(long/2)
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add c
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ld (LONG_MAX),a ; long maximum = 150% of long
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ld a,(SHORT_AVG)
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ld c,a
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ld a,(LONG_AVG)
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add c
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inc a
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srl a ; ceil((short+long)/2)
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ld (LONG_MIN),a ; midpoint belongs to long
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dec a
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ld (SHORT_MAX),a ; short ends below midpoint
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ret
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; -------------------------------------------------------
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@@ -148,7 +159,7 @@ make_window:
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; carry is error, a contains error code
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; -------------------------------------------------------
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calibrate:
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ld a,(TAPE_PORT) ; get current state
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in a,(TAPE_PORT) ; get current state
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ld d,a
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call sample_pulse ; make sure we start in silence
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jp nc,cal_err ; should timeout
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@@ -169,11 +180,6 @@ calibrate:
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call average8
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jr c,cal_err_short_leader_average
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ld (SHORT_AVG),a
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call make_window
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ld a,b
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ld (SHORT_MIN),a
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ld a,c
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ld (SHORT_MAX),a
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; find the long leader
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; need 8 consecutive pulses > short*1.5
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ld a,(SHORT_AVG)
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@@ -201,11 +207,6 @@ calibrate:
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call average8
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jr c,cal_err_long_leader_average
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ld (LONG_AVG),a
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call make_window
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ld a,b
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ld (LONG_MIN),a
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ld a,c
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ld (LONG_MAX),a
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; A quick sanity check: long>1.5*short
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ld a,(SHORT_AVG)
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ld c,a
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@@ -215,29 +216,31 @@ calibrate:
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ld a,(LONG_AVG)
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cp c
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jr c,cal_err_sanity_check
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; Find the marker. marker is 2*long
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; threshold is 1.5*long
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ld a,(LONG_AVG)
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call make_windows
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; Find the marker: 8 consecutive short intervals
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; Classify them using short*1.5
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ld a,(SHORT_AVG)
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ld c,a
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srl a
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add c
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ld c,a ; c = 1.5*long
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; Find two consecutive marker-width intervals
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ld c,a ; c = 1.5*short
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ld e,0 ; consecutive short counter
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5$:
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ld e,0
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6$:
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call measure_pulse
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jr c,cal_err_marker_measure
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ld a,b
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cp c
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jr c,5$ ; not a marker
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inc e ; marker interval found
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jr c,6$ ; short interval found
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ld e,0 ; long interval, restart marker
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jr 5$
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6$:
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inc e
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ld a,e
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cp 2 ; we need two of them
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jr c,6$ ; not 2 yet, measure next
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; both marker halves found
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cp 8
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jr c,5$
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; marker found
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; we are at the beginning of the first data pulse
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; next 8 bytes is the training byte 0x55
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; next byte is the training byte 0x55
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call read_byte
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jr c,cal_err_training_read
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cp a,055h
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@@ -348,22 +351,23 @@ read_byte:
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; -------------------------------------------------------
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; Read and check sync bytes
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; carry is error
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; carry is error, error value in a
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; -------------------------------------------------------
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read_sync:
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call read_byte
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ret c
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jr c,sync_err_read_1
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cp 05ah
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jr nz,9$
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jr nz,sync_err_value_1
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call read_byte
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ret c
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jr c,sync_err_read_2
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cp 0c3h
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jr nz,9$
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jr nz,sync_err_value_2
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or a
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ret
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9$:
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scf
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ret
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create_error_return sync_err_read_1, 001h
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create_error_return sync_err_read_2, 002h
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create_error_return sync_err_value_1, 003h
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create_error_return sync_err_value_2, 004h
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; -------------------------------------------------------
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; Read a block into BLOCK_BUFFER
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@@ -379,6 +383,8 @@ read_block:
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push de
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push hl
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exx
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call BIOS_FLUSH
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di
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; calibrate reader
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call calibrate
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jr nc,1$ ; if no error jump
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@@ -390,6 +396,7 @@ read_block:
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; calibrated, read sync bytes
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call read_sync
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jr nc,2$ ; if no error jump
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ld b,a
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ld a,BLOCK_ERROR_SYNC
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scf
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jr 101$
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@@ -400,10 +407,13 @@ read_block:
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ld hl,BLOCK_BUFFER
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exx
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4$:
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call read_byte
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call read_byte ; byte in a
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jr nc,5$
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; read error
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exx
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ld a,e
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exx
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ld b,a ; store count in block in specific error
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ld a,BLOCK_ERROR_READ
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scf
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jr 101$
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@@ -440,6 +450,7 @@ read_block:
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pop hl
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pop de
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exx
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ei
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ret
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; -------------------------------------------------------
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@@ -455,6 +466,7 @@ read_block_dry:
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push de
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push hl
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exx
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di
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; calibrate reader
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call calibrate
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jr nc,1$ ; if no error jump
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@@ -496,6 +508,7 @@ read_block_dry:
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pop hl
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pop de
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exx
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ei
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ret
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; -------------------------------------------------------
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; CRC16
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