Apple2-IO-RPi/Apple2/DriveFirmware.asm

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3.5 KiB
NASM
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;ProDOS Zero Page
Command = $42 ;ProDOS Command
Unit = $43 ;ProDOS unit (SDDD0000)
BufferLo = $44
BufferHi = $45
BlockLo = $46
BlockHi = $47
; ProDOS Error Codes
IOError = $27
NoDevice = $28
WriteProtect = $2B
InputByte = $c08e+SLOT*$10
OutputByte = $c08d+SLOT*$10
InputFlags = $c08b+SLOT*$10
OutputFlags = $c087+SLOT*$10
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ReadBlockCommand = $01
WriteBlockCommand = $02
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GetTimeCommand = $03
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ChangeDriveCommand = $04
ExecCommand = $05
LoadFileCommand = $06
SaveFileCommand = $07
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.org SLOT*$100 + $C000
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;ID bytes for booting and drive detection
cpx #$20 ;ID bytes for ProDOS and the
cpx #$00 ; Apple Autostart ROM
cpx #$03 ;
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ldx #SLOT*$10
stx $2b
stx Unit
;force EPROM to second page on boot
lda #$3f ;set all flags high and page 3 of EPROM for menu
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PageJump:
sta OutputFlags
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jmp Start ;this jump is only called if coming in from PageJump with A=$0f
;entry points for ProDOS
DriverEntry:
lda #$0f ;set all flags high and page 0 of EPROM
sta OutputFlags
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jmp Driver
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;load first two blocks and execute to boot
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Start:
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lda #$01 ;set read command
sta Command
lda #$00 ;block 0
sta BlockLo
sta BlockHi
sta BufferLo ;buffer at $800
lda #$08
sta BufferHi
jsr Driver ;get the block
jmp $801 ;execute the block
; ProDOS Driver code
; First check that this is the right drive
Driver:
ldx Unit
lda Command; Check which command is being requested
beq GetStatus ;0 = Status command
cmp #ReadBlockCommand
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beq ReadBlockAndSetTime
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cmp #WriteBlockCommand
beq WriteBlock
sec ;set carry as we don't support any other commands
lda #$53 ;Invalid parameter error
rts
; ProDOS Status Command Handler
GetStatus:
ldx #$ff ;low byte number of blocks
ldy #$ff ;high byte number of blocks
lda #$0 ;zero accumulator and clear carry for success
clc
rts
; ProDOS Read Block Command
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ReadBlockAndSetTime:
lda BlockHi ; only get the time if block 0002
bne readBlock
lda BlockLo
cmp #$02
bne readBlock
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ldy #$00 ;Get the current time on each block read for now
lda #GetTimeCommand
jsr SendByte
getTimeByte:
jsr GetByte
sta $bf90,y
iny
cpy #$04
bne getTimeByte
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readBlock:
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lda #ReadBlockCommand ;read the block after setting the clock
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jsr SendByte
lda BlockLo
jsr SendByte
lda BlockHi
jsr SendByte
ldy #$0
jsr read256
inc BufferHi
jsr read256
dec BufferHi
lda #$0 ;zero accumulator and clear carry for success
clc
rts
read256:
jsr GetByte
sta (BufferLo),y
iny
bne read256
rts
; ProDOS Write Block Command
WriteBlock:
lda #WriteBlockCommand
jsr SendByte
lda BlockLo
jsr SendByte
lda BlockHi
jsr SendByte
ldy #$0
jsr write256
inc BufferHi
jsr write256
dec BufferHi
lda #$0 ;zero accumulator and clear carry for success
clc
rts
write256:
lda (BufferLo),y
jsr SendByte
iny
bne write256
rts
SendByte:
pha
waitWrite:
lda InputFlags
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rol
rol
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bcs waitWrite
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pla
sta OutputByte
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lda #$0e ; set bit 0 low to indicate write started
sta OutputFlags
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finishWrite:
lda InputFlags
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rol
rol
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bcc finishWrite
lda #$0f
sta OutputFlags
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rts
GetByte:
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lda #$0d ;set read flag low
sta OutputFlags
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waitRead:
lda InputFlags
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rol
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bcs waitRead
lda InputByte
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pha
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lda #$0f ;set all flags high
sta OutputFlags
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finishRead:
lda InputFlags
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rol
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bcc finishRead
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pla
end:
rts
.repeat 251-<end
.byte 0
.endrepeat
.byte 0,0 ;0000 blocks = check status
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.byte 7 ;bit set(0=status 1=read 2=write) unset(3=format, 4/5=number of volumes, 6=interruptable, 7=removable)
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.byte DriverEntry&$00FF ;low byte of entry