dos33fsprogs/qboot/boot_sector.s
2020-08-21 01:26:14 -04:00

222 lines
3.6 KiB
ArmAsm

; fast seek/multi-read
; copyright (c) Peter Ferrie 2015-16
sectors = 33 ; user-defined
firsttrk = 3 ; user-defined, first track to read
firstsec = 0 ; user-defined, first sector to read
address = $1f ; user-defined
entry = $1f00 ; user-defined
version = 1
;memory usage:
;256 bytes ($bd00-bdff) static table
grouped = $bd00
;106 bytes ($xx00-xx69) static table
preshift = code_end
zvalue = $fd ; only during init
znibble = $fe ; only during init
zmask = $ff ; only during init
; $26/$27 sector read location (ROM)
; $3D sector number (ROM)
; at entry (at least on AppleWin) A=1, X=60, Y=0
; qkumba says cffa cards leave Y at $10
; 26/27 = 00/09
; 3D = 1
; For Disk II booting, the firmware loads track0/sector0
; to $800 and then jumps to $801
.org $800
.byte 1 ; number of sectors for ROM to load
boot_entry:
; this code loads two sectors up to $BE/$BF
lsr ; check sector number
tay
adc #$bd
sta $27 ; set or update address as needed
asl
; be, bf, c0 (1011 1011 1100)
; so if hit $c000 we are done
bmi not_three ; branch if not 3
inc $3d ; increment sector (faster to find)
; call to the read routine in proper slot
; using rts to jump indirect to
; $CX5C
; this routine reads sector in $3D on track $41
; to address in $26/$27
; when it's done it jumps back to $801
txa ; x is slot# << 4
lsr
lsr
lsr
lsr
ora #$c0 ; slot to PROM base
pha
lda #$5b ;read-1
pha
rts
not_three:
; patch self modifying code for Q6L read
txa
ora #$8c ; slot to Q6L
; Q6L?
; if slot 6, after this A is $EC
patch_loop:
iny
ldx patchtbl-3, Y
sta code_begin, X ; replace placeholders with Q6L
; BE02 = EC? lda c0ec
; so sets to c08c (Q6L)
bne patch_loop
; patch self-modifying code for turning motor off
and #$f8 ; MOTOROFF (c088)
sta slotpatch7+1
; patch self-modifying code for phase off
eor #8 ; PHASEOFF (c080)
sta slotpatch8+1
ldx #$3f
stx zmask
inx
ldy #$7f
bne skip_ahead ; branch always
; pad with zeros until $839
; $839 is the entry point
; adjusts address at $8FE to be entry point
; jumps to boot 2
.res $839-*
lda #>(entry-1)
pha
lda #<(entry-1)
pha
jsr preread
jmp $bf00 ; DOS 3.3 launcher entrypoint
patchtbl:
.byte <(slotpatch1+1), <(slotpatch2+1), <(slotpatch3+1)
.byte <(slotpatch4+1), <(slotpatch5+1), <(slotpatch6+1)
indextbl: ;the 0 also terminates the patchtbl list!
.byte 0, 2, 1, 3
;construct denibbilisation table
;pre-shifted for interleave read
skip_ahead:
loopaa:
sty znibble
tya
asl
bit znibble
beq loopz
ora znibble
eor #$ff
and #$7e
loopa:
bcs loopz
lsr
bne loopa
dex
txa
asl
asl
sta preshift-$16, Y
loopz:
dey
bne loopaa
;construct 2-bit group table
sty zvalue
loopbb:
lsr zmask
lsr zmask
loopb:
lda indextbl, X
sta grouped, Y
inc zvalue
lda zvalue
and zmask
bne loopy
inx
txa
and #3
tax
loopy:
iny
iny
iny
iny
cpy #3
bcs loopb
iny
cpy #3
bcc loopbb
lda #>(entry-1)
pha
lda #<(entry-1)
pha
jsr preread
jmp seekread
preread:
;copy post-read if necessary
;push post-read address here
; pla
; tax
; pla
; tay
; lda #>(postread-1)
; pha
; lda #<(postread-1)
; pha
; tya
; pha
; txa
; pha
lda #<(firsttrk*2)
sta phase+1
ldx #sectors
lda #address
ldy #firstsec
rts
end_code:
.res $8fe-*
; traditionally, entry point to jump to at end of loading
; $be01 in this case
;*=$8fe
.byte $be, 1
.include "stage2.s"