Apple2-IO-RPi/Firmware/Firmware.asm
2020-12-12 23:26:16 -05:00

197 lines
3.0 KiB
NASM

;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
ReadBlockCommand = $01
WriteBlockCommand = $02
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:
lda #ReadBlockCommand
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
lsr
lsr
lsr
lsr
jsr SendNibble
pla
jsr SendNibble
rts
SendNibble:
and #$0F
ora #$70 ;Write bit low
pha
waitWrite:
lda InputByte,x
asl ;Second highest bit goes low when ready
bmi waitWrite
pla
sta OutputByte,x
finishWrite:
lda InputByte,x
asl
bpl finishWrite
lda #$FF
sta OutputByte,x
rts
GetByte:
jsr GetNibble
asl
asl
asl
asl
sta NibbleStorage
jsr GetNibble
and #$0f
ora NibbleStorage
rts
GetNibble:
lda #$b0 ;set read flag low
sta OutputByte,x
waitRead:
lda InputByte,x
bmi waitRead
ora #$f0 ;set all flags high
sta OutputByte,x
pha
finishRead:
lda InputByte,x
bpl finishRead
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