mirror of
https://codeberg.org/cryu/micro-sci-a2-controller
synced 2024-11-29 03:50:35 +00:00
364 lines
14 KiB
ArmAsm
364 lines
14 KiB
ArmAsm
; Disk ][ controller card "BOOT0" code, found in the slot ROM. Reads the
|
|
; BOOT1 code from track 0, sector 0, and jumps to it.
|
|
;
|
|
; Copyright Apple Computer Inc.
|
|
;
|
|
; Written by [a genius...Woz?]
|
|
;
|
|
; Extracted from AppleWin at $C600.
|
|
;
|
|
; Project created by Andy McFadden, using 6502bench SourceGen v1.5
|
|
; Last updated 2020/01/15
|
|
;
|
|
; Converted for use with Micro-SCI repro project 2023 Chris RYU
|
|
|
|
STACK := $0100 ;{addr/256}
|
|
.ifdef SECSIZE_16
|
|
TABLE_ENTRY := $02d6
|
|
.else
|
|
TABLE_ENTRY := BOOT1
|
|
.endif
|
|
|
|
TWOS_BUFFER := $0300 ;{addr/86} ;holds the 2-bit chunks
|
|
CONV_TAB := $0356 ;{addr/128} ;6+2 conversion table
|
|
BOOT1 := $0800 ;{addr/256} ;buffer for next stage of loader
|
|
IWM_PH0_OFF := $c080 ;stepper motor control
|
|
IWM_PH0_ON := $c081 ;stepper motor control
|
|
IWM_MOTOR_ON := $c089 ;starts drive spinning
|
|
IWM_SEL_DRIVE_1 := $c08a ;selects drive 1
|
|
IWM_Q6_OFF := $c08c ;read
|
|
IWM_Q7_OFF := $c08e ;WP sense/read
|
|
MON_WAIT := $fca8 ;delay for (26 + 27*Acc + 5*(Acc*Acc))/2 cycles
|
|
PRERR := $ff2d ; 13-sector only
|
|
MON_IORTS := $ff58 ;JSR here to find out where one is
|
|
|
|
data_ptr := $26 ;{addr/2} ;pointer to BOOT1 data buffer
|
|
slot_index := $2b ;{addr/1} ;slot number << 4
|
|
bits := $3c ;{addr/1} ;temp storage for bit manipulation
|
|
sector := $3d ;{addr/1} ;sector to read
|
|
.ifdef SECSIZE_13
|
|
found_track := $2a ;{addr/1} ;track found
|
|
signature := $b5
|
|
.else
|
|
found_track := $40 ;{addr/1} ;track found
|
|
signature := $96
|
|
.endif
|
|
track := $41 ;{addr/1} ;track to read
|
|
|
|
.org $c600
|
|
ENTRY: ldx #$20 ;20/00/03 is the controller signature
|
|
;
|
|
; Generate a decoder table for 6+2 encoded data.
|
|
;
|
|
; This stores the values $00-$3f in a table on page 3. The byte values that
|
|
; will be decoded are non-consecutive, so the decoder entries occupy various
|
|
; locations from $36c to $3d5. Nearby bytes are left unchanged.
|
|
;
|
|
; We want 64 values that have the high bit set and don't have two consecutive 0
|
|
; bits. This is required by the disk hardware. There are 70 possible values,
|
|
; so we also mandate that there are two adjacent 1 bits, excluding bit 7. (Note
|
|
; that $D5 and $AA, used to identify sector headers, do not meet these criteria,
|
|
; which means they never appear in the encoded data.)
|
|
;
|
|
; In the code below, ASL+BIT+BCS test checks for adjacent 1s: if no two are
|
|
; adjacent, the BIT will be zero. If the high bit is set, ASL will set the
|
|
; carry.
|
|
;
|
|
; When we ORA the original and shifted values together, if there were three
|
|
; adjacent 0s, there will still be at least two adjacent 0s. We EOR to invert
|
|
; the bits, and then look for two adjacent 1s. We do this by just shifting
|
|
; right until a 1 shifts into the carry, and if the A-reg is nonzero we know
|
|
; there were at least two 1 bits. We need to ignore the bits on the ends:
|
|
; nonzero high bit was handled earlier, and the low bit can false-positive
|
|
; because ASL always shifts a 0 in (making it look like a 0 in the low bit is
|
|
; adjacent to another 0), so we just mask those off with the AND.
|
|
;
|
|
; For example, we want to decode $A6 to $07. Y=$07 when X=$26...
|
|
; TXA --> 0010 0110
|
|
; ASL --> 0100 1100 C=0 (high bit is clear)
|
|
; BIT --> Z=0 (only possible with adjacent bits)
|
|
; ORA --> 0110 1110 (adjacent 0s become visible)
|
|
; EOR --> 1001 0001 (turn them into 1s)
|
|
; AND --> 0001 0000 (ignore the hi/lo)
|
|
; LSR --> 0000 1000, repeat until A=0 C=1
|
|
;
|
|
ldy #$00
|
|
.ifdef SECSIZE_16
|
|
ldx #$03
|
|
CreateDecTabLoop:
|
|
stx bits
|
|
txa
|
|
asl A ;shift left, putting high bit in carry
|
|
bit bits ;does shifted version overlap?
|
|
beq reject ;no, doesn't have two adjacent 1s
|
|
ora bits ;merge
|
|
eor #$ff ;invert
|
|
and #$7e ;clear hi and lo bits
|
|
check_dub0: bcs reject ;initial hi bit set *or* adjacent 0 bits set
|
|
lsr A ;shift right, low bit into carry
|
|
bne check_dub0 ;if more bits in byte, loop
|
|
tya ;we have a winner, store Y to memory
|
|
sta CONV_TAB,x ;actual lookup will be on bytes with
|
|
;hi bit set
|
|
iny ; so they'll read from CONV_TAB-128
|
|
reject: inx ;try next candidate
|
|
bpl CreateDecTabLoop
|
|
.else
|
|
CreateDecTabLoop:
|
|
LDA #$03
|
|
STA bits
|
|
CLC
|
|
DEY
|
|
TYA
|
|
LC60B: BIT bits
|
|
BEQ CreateDecTabLoop
|
|
ROL bits
|
|
BCC LC60B
|
|
CPY #$D5 ; $D5 is reserved to indicate header
|
|
BEQ CreateDecTabLoop
|
|
DEX
|
|
TXA
|
|
STA TABLE_ENTRY,Y
|
|
BNE CreateDecTabLoop
|
|
.endif
|
|
;
|
|
; Prep the hardware.
|
|
;
|
|
jsr MON_IORTS ;known RTS
|
|
tsx
|
|
lda STACK,x ;pull hi byte of our address off stack
|
|
.ifdef SECSIZE_13
|
|
pha
|
|
.endif
|
|
asl A ;(we assume no interrupts have hit)
|
|
asl A ;multiply by 16
|
|
asl A
|
|
asl A
|
|
sta slot_index ;keep this around
|
|
tax
|
|
.ifdef SECSIZE_13
|
|
lda #$d0 ; ck fixme
|
|
pha
|
|
.endif
|
|
lda IWM_Q7_OFF,x ;set to read mode
|
|
lda IWM_Q6_OFF,x
|
|
lda IWM_SEL_DRIVE_1,x ;select drive 1
|
|
lda IWM_MOTOR_ON,x ;spin it up
|
|
;
|
|
; Blind-seek to track 0.
|
|
;
|
|
ldy #80 ;80 phases (40 tracks)
|
|
seek_loop: lda IWM_PH0_OFF,x ;turn phase N off
|
|
tya
|
|
and #$03 ;mod the phase number to get 0-3
|
|
asl A ;double it to 0/2/4/6
|
|
ora slot_index ;add in the slot index
|
|
tax
|
|
lda IWM_PH0_ON,x ;turn on phase 0, 1, 2, or 3
|
|
lda #86
|
|
jsr MON_WAIT ;wait 19664 cycles
|
|
dey ;next phase
|
|
bpl seek_loop
|
|
.ifdef SECSIZE_13
|
|
lda #>TWOS_BUFFER
|
|
sta data_ptr+1 ;A-reg is 0 when MON_WAIT returns
|
|
lda #<TWOS_BUFFER
|
|
sta data_ptr ;so we're looking for T=0 S=0
|
|
sta sector
|
|
.else
|
|
sta data_ptr ;A-reg is 0 when MON_WAIT returns
|
|
sta sector ;so we're looking for T=0 S=0
|
|
sta track
|
|
lda #>BOOT1 ;write the output here
|
|
sta data_ptr+1
|
|
.endif
|
|
;
|
|
; Sector read routine.
|
|
;
|
|
; Read bytes until we find an address header (D5 AA 96) or data header (D5 AA
|
|
; AD), depending on which mode we're in.
|
|
;
|
|
; This will also be called by the BOOT1 code read from the floppy disk.
|
|
;
|
|
; On entry:
|
|
; X: slot * 16
|
|
; $26-27: data pointer
|
|
; $3d: desired sector
|
|
; $41: desired track
|
|
;
|
|
ReadSector: clc ;C=0 to look for addr (C=1 for data)
|
|
ReadSector_C: php
|
|
@rdbyte1: lda IWM_Q6_OFF,x ;wait for byte
|
|
bpl @rdbyte1 ;not yet, loop
|
|
@check_d5: eor #$d5 ;is it $d5?
|
|
bne @rdbyte1 ;no, keep looking
|
|
@rdbyte2: lda IWM_Q6_OFF,x ;grab another byte
|
|
bpl @rdbyte2
|
|
cmp #$aa ;is it $aa?
|
|
bne @check_d5 ;no, check if it's another $d5
|
|
nop ;(?)
|
|
@rdbyte3: lda IWM_Q6_OFF,x ;grab a third byte
|
|
bpl @rdbyte3
|
|
cmp #signature ;is it $96?
|
|
beq FoundAddress ;winner
|
|
plp ;did we want data?
|
|
bcc ReadSector ;nope, keep looking
|
|
eor #$ad ;yes, see if it's data prologue
|
|
beq FoundData ;got it, read the data (note A-reg = 0)
|
|
bne ReadSector ;keep looking
|
|
|
|
;
|
|
; Read the sector address data. Four fields, in 4+4 encoding: volume, track,
|
|
; sector, checksum.
|
|
;
|
|
FoundAddress: ldy #$03 ;sector # is the 3rd item in header
|
|
.ifdef SECSIZE_13
|
|
hdr_loop: sty found_track ;store $96, then volume, then track
|
|
.else
|
|
hdr_loop: sta found_track ;store $96, then volume, then track
|
|
.endif
|
|
@rdbyte1: lda IWM_Q6_OFF,x ;read first part
|
|
bpl @rdbyte1
|
|
rol A ;first byte has bits 7/5/3/1
|
|
sta bits
|
|
@rdbyte2: lda IWM_Q6_OFF,x ;read second part
|
|
bpl @rdbyte2
|
|
and bits ;merge them
|
|
dey ;is this the 3rd item?
|
|
.ifdef SECSIZE_13
|
|
bne @rdbyte1 ;nope, keep going
|
|
.else
|
|
bne hdr_loop ;nope, keep going
|
|
.endif
|
|
plp ;pull this off to keep stack in balance
|
|
cmp sector ;is this the sector we want?
|
|
bne ReadSector ;no, go back to looking for addresses
|
|
.ifdef SECSIZE_16
|
|
lda found_track
|
|
cmp track ;correct track?
|
|
bne ReadSector ;no, try again
|
|
.endif
|
|
bcs ReadSector_C ;correct T/S, find data (branch-always)
|
|
|
|
;
|
|
; Read the 6+2 encoded sector data.
|
|
;
|
|
; Values range from $96 - $ff. They must have the high bit set, and must not
|
|
; have three consecutive zeroes.
|
|
;
|
|
; The data bytes are written to disk with a rolling XOR to compute a checksum,
|
|
; so we read them back the same way. We keep this in the A-reg for the
|
|
; duration. The actual value is always in the range [$00,$3f] (6 bits).
|
|
;
|
|
; On entry:
|
|
; A: $00
|
|
;
|
|
FoundData:
|
|
.ifdef SECSIZE_13
|
|
ldy #$9a
|
|
.else
|
|
ldy #86 ;read 86 bytes of data into $300-355
|
|
.endif
|
|
read_twos_loop:
|
|
sty bits ;each byte has 3 sets of 2 bits, encoded
|
|
@rdbyte1: ldy IWM_Q6_OFF,x
|
|
bpl @rdbyte1
|
|
eor TABLE_ENTRY,y ;$02d6 + $96 = $36c, first table entry
|
|
ldy bits
|
|
dey
|
|
.ifdef SECSIZE_13
|
|
sta TABLE_ENTRY,y
|
|
.else
|
|
sta TWOS_BUFFER,y ;store these in our page 3 buffer
|
|
.endif
|
|
bne read_twos_loop
|
|
;
|
|
read_sixes_loop:
|
|
sty bits ;read 256 bytes of data into $800
|
|
@rdbyte2: ldy IWM_Q6_OFF,x ;each byte has the high 6 bits, encoded
|
|
bpl @rdbyte2
|
|
.ifdef SECSIZE_13
|
|
eor TABLE_ENTRY,y
|
|
.else
|
|
eor CONV_TAB-128,y
|
|
.endif
|
|
ldy bits
|
|
sta (data_ptr),y ;store these in the eventual data buffer
|
|
iny
|
|
bne read_sixes_loop
|
|
;
|
|
@rdbyte3: ldy IWM_Q6_OFF,x ;read checksum byte
|
|
bpl @rdbyte3
|
|
.ifdef SECSIZE_13
|
|
eor TABLE_ENTRY,y ;does it match?
|
|
.else
|
|
eor CONV_TAB-128,y ;does it match?
|
|
.endif
|
|
another: bne ReadSector ;no, try to find one that's undamaged
|
|
.ifdef SECSIZE_13
|
|
GRP := $33
|
|
RTS
|
|
|
|
DENIB: TAY
|
|
LC6D2: LDX #0
|
|
LC6D4: LDA BOOT1,Y
|
|
LSR
|
|
ROL TWOS_BUFFER+4*GRP,X
|
|
LSR
|
|
ROL TWOS_BUFFER+3*GRP,X
|
|
STA bits
|
|
LDA (data_ptr),Y
|
|
ASL
|
|
ASL
|
|
ASL
|
|
ORA bits
|
|
STA (data_ptr),Y
|
|
INY
|
|
INX
|
|
CPX #GRP
|
|
BNE LC6D4
|
|
DEC found_track
|
|
BNE LC6D2
|
|
CPY TWOS_BUFFER
|
|
BNE ERROR
|
|
JMP TWOS_BUFFER+1
|
|
ERROR: JMP PRERR
|
|
|
|
.byte $FF
|
|
.else
|
|
;
|
|
; Decode the 6+2 encoding. The high 6 bits of each byte are in place, now we
|
|
; just need to shift the low 2 bits of each in.
|
|
;
|
|
ldy #$00 ;update 256 bytes
|
|
init_x: ldx #86 ;run through the 2-bit pieces 3x (86*3=258)
|
|
decode_loop: dex
|
|
bmi init_x ;if we hit $2ff, go back to $355
|
|
lda (data_ptr),y ;foreach byte in the data buffer...
|
|
lsr TWOS_BUFFER,x ; grab the low two bits from the stuff
|
|
; at $300-$355
|
|
rol A ; and roll them into the low two bits
|
|
; of the byte
|
|
lsr TWOS_BUFFER,x
|
|
rol A
|
|
sta (data_ptr),y
|
|
iny
|
|
bne decode_loop
|
|
;
|
|
; Advance the data pointer and sector number, and check to see if the sector
|
|
; number matches the first byte of BOOT1. If it does, we're done. If not, go
|
|
; read the next sector.
|
|
;
|
|
inc data_ptr+1
|
|
inc sector
|
|
lda sector ;sector we'd read next
|
|
cmp BOOT1 ;is next sector < BOOT1?
|
|
ldx slot_index
|
|
bcc another ;yes, go get another sector
|
|
;(note branch x2)
|
|
; All done, jump to BOOT1 ($0801).
|
|
jmp BOOT1+1
|
|
|
|
.byte 0, 0, 0, 0, 0 ;spare bytes
|
|
.endif
|