dos33fsprogs/megademo/disk/megaload.s

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2018-10-12 04:35:35 +00:00
;fast bootable seek/read, slot 6 version
;copyright (c) Peter Ferrie 2011-2012
; Translated to ca64 by Vince Weaver
chksum = 0 ;otherwise safer but 12 bytes larger
secldr2 = $0e ;14th sector is fastest when loaded from bootsector but can be any of them
seekback = 0 ;set to 1 to enable seek backwards
adrlo = $26 ;constant from boot prom
adrhi = $27 ;constant from boot prom
slot = $2b ;constant from boot prom
tmpsec = $3c ;constant from boot prom
tmpadr = $41
partial2 = $f9 ;copy of partial1
partial1 = $fa ;sectors to read from one track
total = $fb ;total sectors to read
step = $fc ;state for stepper motor
tmptrk = $fd ;temporary copy of current track
curtrk = $fe ;current track (must initialise before calling seek)
phase = $ff ;current phase for seek
addrtbl = $50 ;requires 16 bytes
nibtbl = $2d6 ;constant from boot prom
bit2tbl = $200 ;hard-coded (uses $2aa-$2ff)
maxsec = $10 ;sectors per track, usually 10 but 0b for Olympic Decathlon, 0c for Karateka
;this section is specific to bootsectors
;load second stage sector to $900, enabling track seek
; tax ;1 sector
; lda #secldr2
; ldy #9
; jsr seekread
jmp ldr2
;
seekread: stx total
sta addrtbl
sty tmpadr
calcpart: sec
lda #maxsec
sbc addrtbl
cmp total
bcs L1
tax
L1: stx partial1
stx partial2
callseek: jsr seek - 1 ;(seekret) disabled during boot, increment to enable
ldy addrtbl
ldx #$0f
lda #0
L2: sta addrtbl, x
dex
bpl L2
L3: lda tmpadr
ldx sectbl, y
sta addrtbl, x
inc tmpadr
iny
dec partial1
bne L3
read: ldx #0
read1:
L4: jsr readnib
L5: cmp #$d5
bne L4
jsr readnib
cmp #$aa
bne L5
tay ;we need Y=#$AA later
jsr readnib
eor #$ad ;zero A if match
beq check_mode
;if not #$AD, then #$96 is assumed
ldy #2 ;high 8 bits of bit2tbl
sty adrhi ;store 2-bits array at $2xx
L6: jsr readnib
rol ;set carry
sta tmpsec
jsr readnib
and tmpsec
dey
bpl L6
.if chksum
sta tmpsec
tay
ldx addrtbl, y
stx step
.else
tay
lda addrtbl, y
sta step
stx addrtbl, y
tax
.endif
bcs read1
check_mode: cpx #0 ;set carry if non-zero
beq read1
.byte $90
L7: clc
L8: ldx $c0ec
bpl L8
eor nibtbl, x
sta (adrlo), y ;$2xx initially, and then the real address
iny
bne L8
ldx step
stx adrhi ;set real address
bcs L7 ;carry is set on first pass, clear on second, loops one time
.if chksum
L9: ldx $c0ec
bpl L9
eor nibtbl, x
bne read
ldx tmpsec
sta addrtbl, x
.endif
L10: ldx #$a9
L11: inx
beq L10
lda (adrlo), y
lsr bit2tbl, x
rol
lsr bit2tbl, x
rol
sta (adrlo), y
iny
bne L11
dec total
dec partial2
bne read ;read all requested sectors in one track
ldx total
beq seekret
inc phase
inc phase ;update current track
jmp calcpart
sectbl: .byte 0, $0d, $0b, 9, 7, 5, 3, 1, $0e, $0c, $0a, 8, 6, 4, 2, $0f
readnib:
L12: lda $c0ec
bpl L12
seekret: rts ;hard-coded relative to seek
seek: lda #0
sta step
copy_cur: lda curtrk
sta tmptrk
sec
sbc phase
beq seekret
.if seekback
bcs L13
.endif
eor #$ff
inc curtrk
.if seekback
bcc L14
L13: adc #$fe
dec curtrk
L14:
.endif
cmp step
bcc L15
lda step
L15: cmp #8
bcs L16
tay
sec
L16: lda curtrk
ldx step1, y
bne L18
L17: clc
lda tmptrk
ldx step2, y
L18: stx tmpsec
and #3
rol
tax
sta $c0e0, x
L19: ldx #$13
L20: dex
bne L20
dec tmpsec
bne L19
lsr
bcs L17
inc step
bne copy_cur
step1: .byte 1, $30, $28, $24, $20, $1e, $1d, $1c
step2: .byte $70, $2c, $26, $22, $1f, $1e, $1d, $1c
newtrk = $36 ;track*2 for main stage
newnum = $80 ;number of sectors in main stage
newsec = 0 ;first sector in main stage
newadr = $40 ;load address for main stage
newstart = $4000 ;start address for main stage
ldr2: ;jmp ldr2
;replace with something like the following:
inc callseek + 1
lda #$50
sta curtrk
lda #0
sta phase
jsr seek
ldy #0
sty curtrk
lda #newtrk
sta phase
ldx #newnum
lda #newsec
ldy #newadr
jsr seekread
; jmp newstart
ldr3: jmp ldr3