210 lines
3.8 KiB
NASM
210 lines
3.8 KiB
NASM
; Copyright Terence J. Boldt (c)2020-2024
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; Use of this source code is governed by an MIT
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; license that can be found in the LICENSE file.
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; This file contains the source for the firmware
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; that allows the Apple II to boot from the card
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; and for ProDOS to recognize the card as two
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; hard drivers
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;ProDOS Zero Page
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Command = $42 ;ProDOS Command
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Unit = $43 ;ProDOS unit (SDDD0000)
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BufferLo = $44
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BufferHi = $45
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BlockLo = $46
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BlockHi = $47
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; ProDOS Error Codes
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IOError = $27
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NoDevice = $28
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WriteProtect = $2B
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InputByte = $c08e+SLOT*$10
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OutputByte = $c08d+SLOT*$10
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InputFlags = $c08b+SLOT*$10
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OutputFlags = $c087+SLOT*$10
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ReadBlockCommand = $01
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WriteBlockCommand = $02
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GetTimeCommand = $03
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ChangeDriveCommand = $04
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ExecCommand = $05
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LoadFileCommand = $06
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SaveFileCommand = $07
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MenuCommand = $08
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.org SLOT*$100 + $C000
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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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cpx #$00 ; Apple Autostart ROM
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cpx #$03 ;
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ldx #SLOT*$10
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stx $2b
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stx Unit
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;force EPROM to second page on boot
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lda #$3f ;set all flags high and page 3 of EPROM for menu
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PageJump:
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sta OutputFlags
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jmp Start ;this jump is only called if coming in from PageJump with A=$0f
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;entry points for ProDOS
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DriverEntry:
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lda #$0f ;set all flags high and page 0 of EPROM
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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
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sta Command
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lda #$00 ;block 0
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sta BlockLo
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sta BlockHi
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sta BufferLo ;buffer at $800
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lda #$08
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sta BufferHi
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jsr Driver ;get the block
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jmp $801 ;execute the block
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; ProDOS Driver code
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; First check that this is the right drive
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Driver:
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ldx Unit
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lda Command; Check which command is being requested
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beq GetStatus ;0 = Status command
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cmp #ReadBlockCommand
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beq ReadBlockAndSetTime
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cmp #WriteBlockCommand
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beq WriteBlock
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sec ;set carry as we don't support any other commands
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lda #$53 ;Invalid parameter error
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rts
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; ProDOS Status Command Handler
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GetStatus:
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ldx #$ff ;low byte number of blocks
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ldy #$ff ;high byte number of blocks
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lda #$0 ;zero accumulator and clear carry for success
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clc
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rts
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; ProDOS Read Block Command
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ReadBlockAndSetTime:
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lda BlockHi ; only get the time if block 0002
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bne readBlock
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lda BlockLo
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cmp #$02
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bne readBlock
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ldy #$00 ;Get the current time on each block read for now
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lda #GetTimeCommand
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jsr SendByte
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getTimeByte:
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jsr GetByte
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sta $bf90,y
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iny
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cpy #$04
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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
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lda BlockLo
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jsr SendByte
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lda BlockHi
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jsr SendByte
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txa
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jsr SendByte
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ldy #$0
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jsr read256
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inc BufferHi
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jsr read256
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dec BufferHi
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lda #$0 ;zero accumulator and clear carry for success
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clc
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rts
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read256:
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jsr GetByte
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sta (BufferLo),y
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iny
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bne read256
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rts
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; ProDOS Write Block Command
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WriteBlock:
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lda #WriteBlockCommand
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jsr SendByte
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lda BlockLo
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jsr SendByte
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lda BlockHi
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jsr SendByte
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txa
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jsr SendByte
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ldy #$0
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jsr write256
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inc BufferHi
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jsr write256
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dec BufferHi
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lda #$0 ;zero accumulator and clear carry for success
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clc
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rts
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write256:
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lda (BufferLo),y
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jsr SendByte
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iny
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bne write256
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rts
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SendByte:
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pha
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waitWrite:
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lda InputFlags
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rol
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rol
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bcs waitWrite
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pla
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sta OutputByte
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lda #$0e ; set bit 0 low to indicate write started
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sta OutputFlags
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finishWrite:
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lda InputFlags
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rol
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rol
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bcc finishWrite
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lda #$0f
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sta OutputFlags
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rts
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GetByte:
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lda #$0d ;set read flag low
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sta OutputFlags
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waitRead:
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lda InputFlags
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rol
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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
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finishRead:
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lda InputFlags
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rol
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bcc finishRead
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pla
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end:
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rts
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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 23 ;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
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