ProDOS-ROM-Drive/Firmware/Firmware.asm
Terence Boldt 678e68b1c4 Update driver to not need JSR $FF58 on entry
Save and restore zero page values
2022-07-12 18:32:24 -04:00

207 lines
3.9 KiB
NASM

;i/o ports to write to
writeLatchHigh = $C081
writeLatchLow = $C080
;ProDOS defines
command = $42 ;ProDOS command
unit = $43 ;7=drive 6-4=slot 3-0=not used
buflo = $44 ;low address of buffer
bufhi = $45 ;hi address of buffer
blklo = $46 ;low block
blkhi = $47 ;hi block
ioerr = $27 ;I/O error code
nodev = $28 ;no device connected
wperr = $2B ;write protect error
;for relocatable code
ioAddressLo = $FA
ioAddressHi = $FB
tempY = $FC
blockHalfCounter = $FD
lowLatch = $FE
highLatch = $FF
knownRts = $FF58
.org $C700
;code is relocatable
; but set to $c700 for
; readability
;ID bytes for booting and drive detection
cpx #$20 ;ID bytes for ProDOS and the
ldy #$00 ; Apple Autostart ROM
cpx #$03 ;
cpx #$3C ;this one for older II's
;zero out block numbers and buffer address
sty buflo
sty blklo
sty blkhi
iny ;set command = 1 for read block
sty command
jsr knownRts ;jump to known RTS to get our address from the stack
tsx
lda $0100,x ;this for example would be $C7 in slot 7
sta bufhi ;keep the slot here
asl
asl
asl
asl
sta unit
;display copyright message
ldy #<text
drawtxt:
lda (buflo),y
beq boot
sta $07D0-<text,y ;put text on last line
iny
bne drawtxt
;load block 0000 at $0800
boot:
lda #$08 ;push $0800 onto the stack so an RTS will run at $0801
sta bufhi
pha
lda #$00
pha
;This is the ProDOS entry point for this card
entry:
ldx unit ;make sure it's drive 1
bpl docmd ;yep, do command
sec ;nope, set device not connected
lda #nodev
rts ;go back to ProDOS
docmd:
lda command
beq getstat ;command 0 is GetStatus
cmp #$01
beq readblk ;command 1 is ReadBlock
sec ;Format/Write not permitted
lda #wperr ;write protect error
rts ;go back to ProDOS
getstat:
clc ;send back status
lda #$00 ;good status
ldx #$00 ;1024 blocks
ldy #$04 ;
rts
readblk:
lda ioAddressLo
pha
lda ioAddressHi
pha
lda tempY
pha
lda blockHalfCounter
pha
lda lowLatch
pha
lda highLatch
pha
lda blkhi ;get hi block
asl a ;shift up to top 3 bits
asl a ;since that's all the high
asl a ;blocks we can handle
asl a ;
asl a ;
sta highLatch
lda blklo ;get low block
lsr a ;shift so we get the top 5
lsr a ;bits - this also goes in
lsr a ;the high latch
ora highLatch ;add it to those top 3 bits
sta highLatch ;save it back in scratch ram
sta writeLatchHigh,x ;set high latch for card
lda blklo ;get low block
asl a ;shift it to top 3 bits
asl a ;
asl a ;
asl a ;
asl a ;
sta lowLatch
lda #$02
sta blockHalfCounter
lda #$C0
sta ioAddressHi
;This gets 256 bytes from the ROM card
read256:
ldy #$00
loop256:
lda lowLatch
sta writeLatchLow,x
txa
ora #$80
sta ioAddressLo
loop16:
sty tempY
ldy #$00
lda (ioAddressLo),y
ldy tempY
sta (buflo),y
iny
inc ioAddressLo
lda ioAddressLo
and #$0F
bne loop16
continue256:
inc lowLatch
cpy #$00
bne loop256
dec blockHalfCounter
bne readnext256
finish:
pla
sta highLatch
pla
sta lowLatch
pla
sta blockHalfCounter
pla
sta tempY
pla
sta ioAddressHi
pla
sta ioAddressLo
dec bufhi
clc ;clear error code for success
lda #$00
rts
readnext256:
inc bufhi ; set buffer to receive next 256 bytes
clc ; effectively a branch always
bcc read256
;macro for string with high-bit set
.macro aschi str
.repeat .strlen (str), c
.byte .strat (str, c) | $80
.endrep
.endmacro
text: aschi "ROM-Drive (c)1998-2022 Terence J. Boldt"
end:
.byte 0
; These bytes need to be at the top of the 256 byte firmware as ProDOS
; uses these to find the entry point and drive capabilities
.repeat 251-<end
.byte 0
.endrepeat
.byte 0,0 ;0000 blocks = check status
.byte 3 ;bit 0=read 1=status
.byte <entry ;low byte of entry