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Peter Ferrie
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216846b1d8
387
QBOOT.S
Normal file
387
QBOOT.S
Normal file
@ -0,0 +1,387 @@
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;fast seek/multi-read
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;copyright (c) Peter Ferrie 2015
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;assemble using ACME
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!cpu 6502
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!to "qboot",plain
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*=$800
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sectors = $d1 ;user-defined
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firsttrk = $d1 ;user-defined, first track to read
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firstsec = $d1 ;user-defined, first sector to read
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address = $d1 ;user-defined
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entry = $d1d1 ;user-defined
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stkread = 0 ;set to 1 to allow reading into stack page
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seekback = 0 ;set to 1 to enable seek backwards
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version = 1
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;memory usage:
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;256 bytes ($bd00-bdff) static table
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grouped = $bd00
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;106 bytes ($xx00-xx69) static table
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preshift = code_end
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zvalue = $fd ;only during init
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znibble = $fe ;only during init
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zmask = $ff ;only during init
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!byte 1 ;we'll read the other two ourselves
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lsr ;check sector number
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;the following TAY is a workaround for a CFFA bug
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;the bug is that Y isn't zero on entry
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;the workaround sets it to two instead
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;it's not zero, but it's better than #$10
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tay
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adc #$bd
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sta $27 ;set or update address as needed
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asl
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bmi + ;branch if not 3
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inc $3d ;increment sector (faster to find)
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txa
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lsr
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lsr
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lsr
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lsr
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ora #$c0 ;slot to PROM base
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pha
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lda #$5b ;read-1
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pha
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rts
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+ txa
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ora #$8c ;slot to Q6L
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- iny
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ldx patchtbl-3, y
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sta code_begin, x ;replace placeholders with Q6L
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bne -
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and #$f8 ;MOTOROFF
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sta slotpatch7+1
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eor #8 ;PHASEOFF
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sta slotpatch8+1
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ldx #$3f
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stx zmask
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inx
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ldy #$7f
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bne + ;branch always
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*=$839
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jsr preread
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jmp $bf00 ;DOS 3.3 launcher entrypoint
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patchtbl
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!byte <(slotpatch1+1), <(slotpatch2+1), <(slotpatch3+1), <(slotpatch4+1), <(slotpatch5+1), <(slotpatch6+1)
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indextbl ;the 0 also terminates the patchtbl list!
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!byte 0, 2, 1, 3
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;construct denibbilisation table
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;pre-shifted for interleave read
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+
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-- sty znibble
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tya
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asl
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bit znibble
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beq +
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ora znibble
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eor #$ff
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and #$7e
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- bcs +
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lsr
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bne -
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dex
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txa
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asl
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asl
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sta preshift-$16, y
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+ dey
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bne --
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sty curtrk+1
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;construct 2-bit group table
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sty zvalue
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-- lsr zmask
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lsr zmask
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- lda indextbl, x
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sta grouped, y
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inc zvalue
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lda zvalue
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and zmask
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bne +
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inx
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txa
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and #3
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tax
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+ iny
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iny
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iny
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iny
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cpy #3
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bcs -
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iny
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cpy #3
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bcc --
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preread
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lda #>(entry-1)
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pha
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lda #<(entry-1)
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pha
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;copy post-read if necessary
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;push post-read address here
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lda #<(firsttrk*2)
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sta phase+1
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ldx #sectors
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ldy #address
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lda #firstsec
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!if seekback { ;no room to do this in the routine
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sta startsec+1
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stx total+1
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sty tmpadr+1
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}
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jmp seekread
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*=$8fe
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!byte $be, 1
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;the following lives on sectors $0E and $0D
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!pseudopc $be00 {
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code_begin
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!byte version
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readnib
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slotpatch1
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- lda $c0d1
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bpl -
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rts
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;fill address array for one track
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seekread
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!if seekback=0 {
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sta startsec+1
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stx total+1
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sty tmpadr+1
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}
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inittrk
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sec
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lda #$10
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sbc startsec+1
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cmp total+1
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bcs +
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tax
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+ stx partial1
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stx partial2
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jsr seek
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startsec
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ldy #$d1
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tmpadr
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- lda #$d1
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sta addrtbl, y
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inc tmpadr+1
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iny
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dec partial1
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bne -
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read
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-- jsr readnib
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- cmp #$d5
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bne --
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jsr readnib
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cmp #$aa
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bne -
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tay ;we need Y=#$AA later
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jsr readnib
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eor #$ad ;zero A if match
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beq check_mode
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;if not #$AD, then #$96 is assumed
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ldy #2 ;volume, track, sector
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- jsr readnib
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rol ;set carry
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sta sector+1
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jsr readnib
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and sector+1
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dey
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bpl -
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tay
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ldx addrtbl, y ;fetch corresponding address
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beq read
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sta sector+1 ;store index for later
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stx adrpatchx5+2
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stx adrpatch6+2
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stx adrpatchx1+2
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stx adrpatchx2+2
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stx adrpatchx3+2
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stx adrpatchx4+2
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inx
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stx adrpatchx6+2
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dex
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dex
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stx adrpatch3+2
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stx adrpatch5+2
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!if stkread {
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inx
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}
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ldy #$fe
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adrpatchx5
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- lda $d102, y
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pha
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iny
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bne -
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branch_read
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bcs read ;branch always
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check_mode
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cpx #0
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beq read ;loop if not expecting #$AD
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-- sta tmpval+1 ;zero rolling checksum
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slotpatch2
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- ldx $c0d1
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bpl -
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lda preshift-$96, x
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adrpatchx1
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sta $d102, y ;store 2-bit array
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tmpval
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eor #$d1
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iny
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bne --
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ldy #$aa
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slotpatch3
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- ldx $c0d1
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bpl -
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eor preshift-$96, x
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adrpatchx2
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ldx $d102, y ;bit2tbl
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eor grouped+2, x ;first 86 nibbles use group bits 0-1
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adrpatch3
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sta $d156, y
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iny
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bne -
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and #$fc
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ldy #$aa
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slotpatch4
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- ldx $c0d1
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bpl -
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eor preshift-$96, x
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adrpatchx3
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ldx $d102, y ;bit2tbl
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eor grouped+1, x ;second 86 nibbles use group bits 2-3
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adrpatch5
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sta $d1ac, y
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iny
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bne -
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and #$fc
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ldx #$ac
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slotpatch5
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- ldy $c0d1
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bpl -
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eor preshift-$96, y
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adrpatchx4
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ldy $d100, x ;bit2tbl
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eor grouped, y ;last 84 nibbles use group bits 4-5
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adrpatch6
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sta $d100, x
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inx
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bne -
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and #$fc
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slotpatch6
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- ldy $c0d1
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bpl -
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eor preshift-$96, y
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cmp #1 ;carry = !zero
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ldy #1
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- pla
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adrpatchx6
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sta $d100, y
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dey
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bpl -
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branch_read2
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bcs branch_read ;branch if checksum failure
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sector
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ldy #$d1
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txa
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sta addrtbl, y ;zero corresponding address
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dec total+1
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dec partial2 ;adjust remaining count (faster than looping over array)
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sec
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bne branch_read2 ;read all requested sectors in one track
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total
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ldx #$d1
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beq driveoff
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inc phase+1
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inc phase+1 ;update current track
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jmp inittrk
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driveoff
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slotpatch7
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lda $c0d1
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seekret
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rts
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seek
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lda #0
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sta step+1
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copy_cur
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curtrk
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lda #$d1
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sta tmpval+1
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sec
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phase
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sbc #$d1
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beq seekret
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!if seekback {
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bcs +
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}
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eor #$ff
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inc curtrk+1
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!if seekback {
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bcc ++
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+ adc #$fe
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dec curtrk+1
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++
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}
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cmp step+1
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bcc +
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step
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lda #$d1
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+ cmp #8
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bcs +
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tay
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sec
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+ lda curtrk+1
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ldx step1, y
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bne +
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--- clc
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lda tmpval+1
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ldx step2, y
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+ stx sector+1
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and #3
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rol
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tax
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slotpatch8
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sta $c0d1, x
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-- ldx #$13
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- dex
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bne -
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dec sector+1
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bne --
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lsr
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bcs ---
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inc step+1
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bne copy_cur
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step1 !byte 1, $30, $28, $24, $20, $1e, $1d, $1c
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step2 !byte $70, $2c, $26, $22, $1f, $1e, $1d, $1c
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addrtbl !fill 16
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partial1 = *
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partial2 = partial1+1
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code_end=partial2+1
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}
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10
README.md
Normal file
10
README.md
Normal file
@ -0,0 +1,10 @@
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- targets multi-loaders in ProDOS order
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- load from any slot
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- scatter-reads sectors
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- sector-level read, can start and end anywhere in a track
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- can perform full-track read in one revolution
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- no zpage usage after init
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- only 2 bytes overhead per read
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- can load up to $bc sectors at a time ($0100-bcff)
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- DOS 3.3 Launcher compatible
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- requires only 3 pages in memory
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