dos33fsprogs/mist/qboot_stage2.s

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; the following lives on sectors $0E and $0D
; why?
; request sector 2 and 4, and the interleave is
; beneath apple dos (3-23)
; Physical (firmware) : 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
; DOS33 mapping : 0, 7, 14, 6, 13, 5, 12, 4, 11, 3, 10, 2, 9, 1, 8, 15
; Beneath Apple DOS
; p86 (dos reference)
;
WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
.org $1000
code_begin:
.byte version
readnib:
slotpatch1: ; smc
lda $c0d1 ; gets set to C08C (Q6L) read
bpl readnib
rts
;fill address array for one track
seekread:
sty startsec+1
sta tmpadr+1
stx total+1
inittrk:
sec
lda #$10
sbc startsec+1
cmp total+1
bcs it_skip
tax
it_skip:
stx partial1
stx partial2
jsr seek
startsec:
ldy #$d1
tmpadr:
tmpadr_loop:
lda #$d1
sta addrtbl, y
inc tmpadr+1
iny
dec partial1
bne tmpadr_loop
;====================================
; read a sector
;====================================
; first address field
;====================================
; starts with $D5 $AA $96
; then XX YY volume
; then XX YY track
; then XX YY sector
; then XX YY checksum
; then ends with $DE $AA $EB
;====================================
; data field
;====================================
; starts with $D5 $AA $AD
; 342 bytes of data
; XX checksum
; ends with $DE $AA $EB
read:
outer_read:
jsr readnib
inner_read:
cmp #$d5 ; look for $D5 part of addr field
bne outer_read
jsr readnib ; look for $D5 $AA
cmp #$aa
bne inner_read
; look for $D5 $AA $AD
tay ; we need Y=#$AA later
jsr readnib
eor #$ad ; zero A if match
beq check_mode
; if not #$AD, then #$96 is assumed
; so in address field
ldy #2 ; volume, track, sector
another:
jsr readnib
rol ; set carry
sta sector+1
jsr readnib
and sector+1
dey
bpl another
tay
ldx addrtbl, Y ; fetch corresponding address
beq read ; done?
sta sector+1 ; store index for later
stx adrpatch1+2
stx adrpatch8+2
stx adrpatch2+2
stx adrpatch3+2
stx adrpatch5+2
stx adrpatch7+2
inx
stx adrpatch9+2
dex
dex
stx adrpatch4+2
stx adrpatch6+2
ldy #$fe
loop2:
adrpatch1:
lda $d102, Y
pha
iny
bne loop2
branch_read:
bcs read ; branch always
check_mode:
cpx #0
beq read ; loop if not expecting #$AD
loop33:
sta tmpval+1 ; zero rolling checksum
slotpatch2:
loop4:
ldx $c0d1
bpl loop4
lda preshift-$96, X
adrpatch2:
sta $d102, Y ; store 2-bit array
tmpval:
eor #$d1
iny
bne loop33
ldy #$aa
slotpatch3:
loop5:
ldx $c0d1
bpl loop5
eor preshift-$96, X
adrpatch3:
ldx $d102, Y ; bit2tbl
eor grouped+2, X ; first 86 nibbles use group bits 0-1
adrpatch4:
sta $d156, y
iny
bne loop5
and #$fc
ldy #$aa
slotpatch4:
loop6:
ldx $c0d1
bpl loop6
eor preshift-$96, X
adrpatch5:
ldx $d102, Y ; bit2tbl
eor grouped+1, X ; second 86 nibbles use group bits 2-3
adrpatch6:
sta $d1ac, Y
iny
bne loop6
and #$fc
ldx #$ac
slotpatch5:
loop7:
ldy $c0d1
bpl loop7
eor preshift-$96, Y
adrpatch7:
ldy $d100, X ; bit2tbl
eor grouped, Y ; last 84 nibbles use group bits 4-5
adrpatch8:
sta $d100, x
inx
bne loop7
and #$fc
slotpatch6:
loop8:
ldy $c0d1
bpl loop8
eor preshift-$96, Y
cmp #1 ; carry = !zero
ldy #1
loop9:
pla
adrpatch9:
sta $d100, Y
dey
bpl loop9
branch_read2:
bcs branch_read ; branch if checksum failure
sector:
ldy #$d1
txa
sta addrtbl, Y ; zero corresponding address
dec total+1
dec partial2 ; adjust remaining count
; (faster than looping over array)
sec
bne branch_read2 ; read all requested sectors in one track
sta startsec+1 ; this was missing from original code
; leading to trouble on wrap around
; it not starting at sector0
total:
ldx #$d1
beq driveoff
inc phase+1
inc phase+1 ; update current track
jmp inittrk
driveoff:
slotpatch7:
lda $c0d1
seekret:
rts
seek:
ldx #0
stx step+1
copy_cur:
curtrk:
lda #0
sta tmpval+1
sec
phase:
sbc #$d1
beq seekret
; if seek backwards
bcs sback
eor #$ff
inc curtrk+1
bcc ssback
sback:
adc #$fe
dec curtrk+1
ssback:
cmp step+1
bcc loop10
step:
lda #$d1
loop10:
cmp #8
bcs loop11
tay
sec
loop11:
lda curtrk+1
ldx step1, Y
bne loop12
loopmmm:
clc
lda tmpval+1
ldx step2, Y
loop12:
stx sector+1
and #3
rol
tax
slotpatch8:
sta $c0d1, X
loopmm:
ldx #$13
loopm:
dex
bne loopm
dec sector+1
bne loopmm
lsr
bcs loopmmm
inc step+1
bne copy_cur
step1: .byte 1, $30, $28, $24, $20, $1e, $1d, $1c
step2: .byte $70, $2c, $26, $22, $1f, $1e, $1d, $1c
addrtbl: .res 16
partial1: .byte $00
partial2: .byte $00
code_end:
;==========================
; enable drive motor
;==========================
driveon:
slotpatch9:
lda $c0d1
; wait 1s
ldx #6
wait_1s:
lda #255
jsr WAIT
dex
bne wait_1s
rts
load_new:
jsr driveon
lda load_track
asl ; track to start*2
sta phase+1
lda load_sector
tay ; sector to start
lda load_length ; length
tax
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lda load_address ; address to load
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jsr seekread
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rts
load_address:
.byte $00
load_track:
.byte $00
load_sector:
.byte $00
load_length:
.byte $00