mirror of
https://github.com/tjboldt/ProDOS-ROM-Drive.git
synced 2024-12-01 00:50:16 +00:00
207 lines
3.9 KiB
NASM
207 lines
3.9 KiB
NASM
;i/o ports to write to
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writeLatchHigh = $C081
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writeLatchLow = $C080
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;ProDOS defines
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command = $42 ;ProDOS command
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unit = $43 ;7=drive 6-4=slot 3-0=not used
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buflo = $44 ;low address of buffer
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bufhi = $45 ;hi address of buffer
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blklo = $46 ;low block
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blkhi = $47 ;hi block
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ioerr = $27 ;I/O error code
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nodev = $28 ;no device connected
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wperr = $2B ;write protect error
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;for relocatable code
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ioAddressLo = $FA
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ioAddressHi = $FB
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tempY = $FC
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blockHalfCounter = $FD
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lowLatch = $FE
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highLatch = $FF
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knownRts = $FF58
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.org $C700
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;code is relocatable
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; but set to $c700 for
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; readability
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;ID bytes for booting and drive detection
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cpx #$20 ;ID bytes for ProDOS and the
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ldy #$00 ; Apple Autostart ROM
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cpx #$03 ;
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cpx #$3C ;this one for older II's
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;zero out block numbers and buffer address
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sty buflo
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sty blklo
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sty blkhi
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iny ;set command = 1 for read block
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sty command
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jsr knownRts ;jump to known RTS to get our address from the stack
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tsx
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lda $0100,x ;this for example would be $C7 in slot 7
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sta bufhi ;keep the slot here
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asl
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asl
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asl
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asl
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sta unit
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;display copyright message
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ldy #<text
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drawtxt:
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lda (buflo),y
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beq boot
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sta $07D0-<text,y ;put text on last line
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iny
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bne drawtxt
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;load block 0000 at $0800
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boot:
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lda #$08 ;push $0800 onto the stack so an RTS will run at $0801
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sta bufhi
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pha
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lda #$00
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pha
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;This is the ProDOS entry point for this card
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entry:
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ldx unit ;make sure it's drive 1
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bpl docmd ;yep, do command
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sec ;nope, set device not connected
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lda #nodev
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rts ;go back to ProDOS
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docmd:
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lda command
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beq getstat ;command 0 is GetStatus
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cmp #$01
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beq readblk ;command 1 is ReadBlock
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sec ;Format/Write not permitted
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lda #wperr ;write protect error
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rts ;go back to ProDOS
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getstat:
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clc ;send back status
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lda #$00 ;good status
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ldx #$00 ;1024 blocks
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ldy #$04 ;
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rts
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readblk:
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lda ioAddressLo
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pha
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lda ioAddressHi
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pha
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lda tempY
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pha
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lda blockHalfCounter
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pha
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lda lowLatch
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pha
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lda highLatch
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pha
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lda blkhi ;get hi block
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asl a ;shift up to top 3 bits
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asl a ;since that's all the high
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asl a ;blocks we can handle
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asl a ;
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asl a ;
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sta highLatch
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lda blklo ;get low block
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lsr a ;shift so we get the top 5
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lsr a ;bits - this also goes in
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lsr a ;the high latch
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ora highLatch ;add it to those top 3 bits
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sta highLatch ;save it back in scratch ram
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sta writeLatchHigh,x ;set high latch for card
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lda blklo ;get low block
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asl a ;shift it to top 3 bits
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asl a ;
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asl a ;
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asl a ;
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asl a ;
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sta lowLatch
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lda #$02
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sta blockHalfCounter
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lda #$C0
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sta ioAddressHi
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;This gets 256 bytes from the ROM card
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read256:
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ldy #$00
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loop256:
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lda lowLatch
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sta writeLatchLow,x
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txa
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ora #$80
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sta ioAddressLo
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loop16:
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sty tempY
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ldy #$00
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lda (ioAddressLo),y
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ldy tempY
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sta (buflo),y
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iny
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inc ioAddressLo
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lda ioAddressLo
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and #$0F
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bne loop16
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continue256:
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inc lowLatch
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cpy #$00
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bne loop256
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dec blockHalfCounter
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bne readnext256
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finish:
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pla
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sta highLatch
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pla
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sta lowLatch
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pla
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sta blockHalfCounter
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pla
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sta tempY
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pla
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sta ioAddressHi
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pla
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sta ioAddressLo
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dec bufhi
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clc ;clear error code for success
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lda #$00
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rts
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readnext256:
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inc bufhi ; set buffer to receive next 256 bytes
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clc ; effectively a branch always
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bcc read256
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;macro for string with high-bit set
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.macro aschi str
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.repeat .strlen (str), c
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.byte .strat (str, c) | $80
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.endrep
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.endmacro
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text: aschi "ROM-Drive (c)1998-2022 Terence J. Boldt"
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end:
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.byte 0
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; These bytes need to be at the top of the 256 byte firmware as ProDOS
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; uses these to find the entry point and drive capabilities
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.repeat 251-<end
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.byte 0
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.endrepeat
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.byte 0,0 ;0000 blocks = check status
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.byte 3 ;bit 0=read 1=status
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.byte <entry ;low byte of entry
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