Apple2-IO-RPi/Firmware/Driver.asm
2020-12-10 22:03:49 +00:00

175 lines
2.7 KiB
NASM

; ProDOS Global Page
Device5S1 = $bf1a ;POINTER FOR SLOT 5 DRIVE 1 DRIVER
DeviceCount = $bf31 ;DEVICE COUNT -1
DeviceList = $bf32 ;DEVICE LIST
; 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 = $c0de
OutputByte = $c0dd
ReadBlockCommand = $01
WriteBlockCommand = $02
NibbleStorage = $1d
.org $1000
; Register the driver with ProDOS
lda #<Driver
sta Device5S1
lda #>Driver
sta Device5S1+1
; Add the drive to the device list
inc DeviceCount
lda DeviceCount
ldy #SlotDrive
sta DeviceList,y
rts
; ProDOS Driver code
; First check that this is the right drive
Driver:
lda Unit
cmp #SlotDrive
beq DoCommand ;correct device, so proceed
sec ;set carry as ProDOS treats this as an error
lda #NoDevice ;put the error code in accumulator for ProDOS
rts
; Check which command is being requested
DoCommand:
lda Command
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 #$70 ;Write bit low
pha
waitWrite:
lda InputByte
asl ;Second highest bit goes low when ready
bmi waitWrite
pla
sta OutputByte
finishWrite:
lda InputByte
asl
bpl finishWrite
lda #$FF
sta OutputByte
rts
GetByte:
jsr GetNibble
asl
asl
asl
asl
sta NibbleStorage
jsr GetNibble
and #$0f
ora NibbleStorage
lda NibbleStorage
rts
GetNibble:
lda #$b0 ;set read flag low
sta OutputByte
waitRead:
lda InputByte
bmi waitRead
ora #$f0 ;set all flags high
sta OutputByte
pha
finishRead:
lda InputByte
bpl finishRead
pla
rts