Apple2-IO-RPi/Apple2/Firmware.asm

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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
SlotDrive = $50
InputByte = $c08e
OutputByte = $c08d
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InputFlags = $c08b
OutputFlags = $c087
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ReadBlockCommand = $01
WriteBlockCommand = $02
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GetTimeCommand = $03
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NibbleStorage = $1d
.org STARTSLOT
;ID bytes for booting and drive detection
cpx #$20 ;ID bytes for ProDOS and the
cpx #$00 ; Apple Autostart ROM
cpx #$03 ;
cpx #$3C ;this one for older II's
;load first two blocks and execute to boot
Boot:
lda #$01 ;set read command
sta Command
jsr $ff58
tsx
lda $0100,x
asl
asl
asl
asl
sta $2b
sta Unit
tax
lda #$00 ;block 0
sta BlockLo
sta BlockHi
sta BufferLo ;buffer at $800
lda #$08
sta BufferHi
jsr Driver ;get the block
; lda #$00 ;block 1
; sta BlockLo
; sta BlockHi
; sta BufferLo ;buffer at $A00
; lda #$0A
; sta BufferHi
; jsr Driver ;get the block
; ldx #sdrive ;set up for slot n
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
beq ReadBlock
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
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
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:
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lda InputFlags,x
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ror
ror ;Second lowest bit goes low when ready
bcs waitWrite
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pla
sta OutputByte,x
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lda #$0e ; set bit 0 low to indicate write started
sta OutputFlags,x
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finishWrite:
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lda InputFlags,x
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ror
ror
bcc finishWrite
lda #$0f
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sta OutputFlags,x
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rts
GetByte:
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lda #$0d ;set read flag low
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sta OutputFlags,x
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waitRead:
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lda InputFlags,x
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ror
bcs waitRead
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lda InputByte
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pha
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lda #$0f ;set all flags high
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sta OutputFlags,x
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finishRead:
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lda InputFlags,x
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ror
bcc finishRead
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pla
end:
rts
.repeat 251-<end
.byte 0
.endrepeat
.byte 0,0 ;0000 blocks = check status
.byte 3 ;bit 0=read 1=status
.byte Driver&$00FF ;low byte of entry