ARP responder

[fpgaboy.git] / ethernet.asm

	INCLUDE "serial.inc"

ETH_STATUS EQU $FF68
ETH_DATA EQU $FF69
ARP_ENTRIES EQU 6
ARP_ENTRY_SIZE EQU 13

	SECTION "config", HOME[$0]
myMAC:	db $12, $34, $56, $78, $9A, $00
myIP:	db $0A, $00, $00, $02
myMask:	db $FF, $00, $00, $00
myGW:	db $0A, $00, $00, $01

	SECTION "boot", HOME[$100]
	jr start
	nop
	nop
	
	db $CE,$ED,$66,$66,$CC,$0D,$00,$0B,$03,$73,$00,$83       ;<<< no $00,$c3,$50,$01
	db $00,$0C,$00,$0D,$00,$08,$11,$1F,$88,$89,$00,$0E,$DC,$CC,$6E,$E6
	db $DD,$DD,$D9,$99,$BB,$BB,$67,$63,$6E,$0E,$EC,$CC,$DD,$DC,$99,$9F
	db $BB,$B9,$33,$3E     ; Standard Nintendo DO NOT CHANGE...

	db "GB Ethernet     "  ; Cart name   16bytes
	db $00,$00,$00         ; Not used
	db $00                 ; Cart type   ROM Only
	db $00                 ; ROM Size    32k
	db $00                 ; RAM Size     0k
	db $cf,$08             ; Maker ID Matthew Johnson
	db $01                 ; Version     =1
	db $87                 ; Complement check (Important)
	db $ff,$ff             ; Cheksum, fix this if you are going to

start:
	ld sp, $D800
	call zerobss
	PUTSIL "Ethernet test ROM"
.lp:	xor a			; Reset state machines
	ld [ETH_STATUS], a
	ld a, [ETH_STATUS]	; Load current status
	ld [$FF51], a
	and $02		; New packet?
	call nz, getpacket
	jr .lp

zerobss:
	ld hl, bssstart
	ld bc, bssend - bssstart
.lp:	ld a, b
	or c
	ret z
	dec bc
	xor a
	ld [hli], a
	ld a, h
	jr .lp

getpacket:
	ld a, [ETH_DATA]
	ld b, a
	ld a, [ETH_DATA]
	ld c, a
	push bc
	ld hl, packet
.cplp:	ld a, b
	or c
	jr z, .done
	dec bc
	ld a, [ETH_DATA]
	ld [hli], a
	jr .cplp
.done:	pop bc
	PUTSI "getpacket: Got "
	PUTHEX b
	PUTHEX c
	PUTSIL " byte packet from hardware."
	ld hl, packet
	call ether_input
	ret

ether_input:
	push hl
	PUTSI "ether_input: Packet to "
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTSI " from "
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTC $3A
	PUTHEX [hli]
	PUTSI " protocol "
	PUTHEX [hli]
	PUTHEX [hli]
	PUTSIL "."
	pop hl
	
	; Verify the destination MAC.
	push hl
	ld de, myMAC
	ld c, $06
.maclp:	ld a, [de]
	cp [hl]
	jr nz, .notus
	inc de
	inc hl
	dec c
	jr nz, .maclp
	; Done? Then it was to us!
	jr .us
.notus:	; Was it to broadcast?
	pop hl
	push hl
	ld c, $06
.bclp:	ld a, [hli]
	cp $FF
	jr nz, .notbc
	dec c
	jr nz, .bclp

.us:	PUTSIL "ether_input: It's to us!"
	; Which protocol does it belong to?
	pop hl
	ld b, $00
	ld c, 12
	add hl, bc	; Skip source and dest MAC.
	ld a, [hli]
	cp $08
	jr nz, .unknownproto
	ld a, [hli]
	cp $06
	jr z, .arp
	cp $00
	jp z, .ip
	jr .unknownproto

.notbc:	pop hl
	PUTSIL "ether_input: Not addressed to us and not broadcast."
	ret
	
.unknownproto:
	PUTSIL "ether_input: Unknown protocol; dropping"
	ret

.arp:
	PUTSIL "ether_input: ARP packet"
	call arp_input
	ret
.ip:
	PUTSIL "ether_input: IP packet"
	call ip_input
	ret

arp_input:
	; First, verify that this is an ARP packet that we can handle.
	ld c, 7
	ld de, .expectedarp
.cklp:	xor a
	cp c
	jr z, .ckdone
	ld a, [de]
	cp [hl]
	jr nz, .badarp
	inc de
	inc hl
	dec c
	jr .cklp
.ckdone:
	ld a, [hli]
	cp 1
	jr z, .req
	cp 2
	jp z, .resp
.badarp:
	PUTSIL "arp_input: Unknown protocol hardware or request"
	ret
.expectedarp:
	db $00, $01, $08, $00, $06, $04, $00

.req:
	PUTSIL "arp_input.req: Request"
	; Is it asking about us?
	push hl
	ld b, 0
	ld c, $10	; SHA + SPA + THA
	add hl, bc
	ld de, myIP
	ld c, 4
.iplp:	ld a, [de]
	cp [hl]
	jp nz, .notourip
	inc de
	inc hl
	dec c
	jr nz, .iplp
	PUTSIL "arp_input.req: Aimed at us."
	pop hl	; Now synthesize a response packet.
	push hl
	dec hl
	ld a, $02	; Reply!
	ld [hli], a
	ld d, h
	ld e, l
	ld hl, 10	; SHA + SPA
	add hl, de	; Now DE points at SHA, and HL points at THA
	ld c, 10
.dcl:	ld a, [de]
	ld [hli], a
	inc de
	dec c
	jr nz, .dcl
	pop hl		; HL now points at SHA
	ld de, myMAC
	ld c, $06
.mcl:	ld a, [de]
	ld [hli], a
	inc de
	dec c
	jr nz, .mcl
	ld de, myIP	; HL now points at SPA
	ld c, $04
.icl:	ld a, [de]
	ld [hli], a
	inc de
	dec c
	jr nz, .icl
	ld d, h
	ld e, l		; HL now points at THA
	ld hl, -32
	add hl, de	; HL has now been backed up to the start of the ethernet header.
	ld d, h
	ld e, l		; DE now points at the dest
	ld hl, 6
	add hl, de	; HL now points at the source
	ld c, $06
.sdcl:	ld a, [hli]
	ld [de], a
	inc de
	dec c
	jr nz, .sdcl
	ld hl, myMAC	; DE now points at the source
	ld c, $06
.smcl:	ld a, [hli]
	ld [de], a
	inc de
	dec c
	jr nz, .smcl
	ld hl, -12
	add hl, de	; HL now points at the start of the packet -- should be C000!
	ld b, 0
	ld c, 64	; Minimum size packet; avoid transmitting a runt
	call packet_send
	PUTSIL "arp_input.req: sent response!"
	ret
.notourip:
	PUTSIL "arp_input.req: Not aimed at us; ignoring."
	pop hl
	ret
	
.resp:
	PUTSIL "arp_input.resp: Response"
	ret

ip_input:
	ret

packet_send:
	ld a, [ETH_STATUS]	; Wait for the port to become available.
	and $01
	jr nz, packet_send
	ld a, b
	ld [ETH_DATA], a
	ld a, c
	ld [ETH_DATA], a
.pkts:	ld a, b
	or c
	ret z
	dec bc
	ld a, [hli]
	ld [ETH_DATA], a
	jr .pkts

	SECTION "ethdata", BSS
bssstart	DS 0
packet		DS 1552
arptable	DS ARP_ENTRIES * ARP_ENTRY_SIZE
bssend		DS 0