Apple2-IO-RPi/Apple2/DriveFirmware.asm
Oliver Schmidt 0ef9d567aa Added support for an alternative hardware type.
The new hardware type has simple UART-type interface. Beside the two data registers, there are only the two bits to indicate readability and writability of the data registers.
2024-02-04 21:45:24 -05:00

205 lines
3.8 KiB
NASM

; Copyright Terence J. Boldt (c)2020-2022
; Use of this source code is governed by an MIT
; license that can be found in the LICENSE file.
; This file contains the source for the firmware
; that allows the Apple II to boot from the card
; and for ProDOS to recognize the card as two
; hard drivers
;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
ReadBlockCommand = $01
WriteBlockCommand = $02
GetTimeCommand = $03
ChangeDriveCommand = $04
ExecCommand = $05
LoadFileCommand = $06
SaveFileCommand = $07
MenuCommand = $08
.org SLOT*$100 + $C000
;ID bytes for booting and drive detection
cpx #$20 ;ID bytes for ProDOS and the
cpx #$00 ; Apple Autostart ROM
cpx #$03 ;
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
PageJump:
sta OutputFlags
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
jmp Driver
;load first two blocks and execute to boot
Start:
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
beq ReadBlockAndSetTime
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
ReadBlockAndSetTime:
lda BlockHi ; only get the time if block 0002
bne readBlock
lda BlockLo
cmp #$02
bne readBlock
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
readBlock:
lda #ReadBlockCommand ;read the block after setting the clock
jsr SendByte
lda BlockLo
jsr SendByte
lda BlockHi
jsr SendByte
txa
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
txa
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:
bit InputFlags
bvs SendByte
sta OutputByte
.if HW_TYPE = 0
lda #$0e ; set bit 0 low to indicate write started
sta OutputFlags
finishWrite:
bit InputFlags
bvc finishWrite
lda #$0f
sta OutputFlags
.endif
rts
GetByte:
.if HW_TYPE = 0
ldx #$0d ;set read flag low
stx OutputFlags
.endif
waitRead:
bit InputFlags
bmi waitRead
lda InputByte
.if HW_TYPE = 0
ldx #$0f ;set all flags high
stx OutputFlags
finishRead:
bit InputFlags
bpl finishRead
.endif
end:
rts
.repeat 251-<end
.byte 0
.endrepeat
.byte 0,0 ;0000 blocks = check status
.byte 23 ;bit set(0=status 1=read 2=write) unset(3=format, 4/5=number of volumes, 6=interruptable, 7=removable)
.byte DriverEntry&$00FF ;low byte of entry