.TITLE	GATNET	Local net interface
	.SBTTL	System and module definitions
	.ENABL	LC
;
; Pdp11/dcn local net interface
;
; This module processes routing updates (hello messages) received from other
; dcnet hosts and gateways. it also generates these messages and sends them
; over each neighbor link. As part of this procedure the physical host logical
; clock is corrected for drift relative to a selected virtual host in the
; network.
;
; Option bits:
; hlobit	send (active mode) hello messages (1)
; gatbit	dcnet clone (0), foreign network (1)
; dwnbit	disable routing (1)
; bstbit	point-to-point (0), broadcast (1)
; dlxbit	measured delay (0), configured delay (1)
; sbnbit	subnet hello
;
; External symbols
;
	.GLOBL	DATSUM		;checksum routine
	.GLOBL	ADRMAP,NETMAP	;routing functions
	.GLOBL	$NETID,$HOSAD,GATVPT ;routing tables
	.GLOBL	$CKHID,$ONLIN,$CKCNT,$ROUTE ;state variables
	.GLOBL	$TRNET,$RTCHG	;trace variables
;
; Entry symbols
;
	.GLOBL	NTIHLO		;local-net control input
	.GLOBL	NTOHLO		;local-net control output
	.GLOBL	ADRPTR		;determine ip address mask
	.GLOBL	NETEST		;test neighbor net
;
; System definitions
;
	.ASECT
	.MCALL	.COM,.PSA,.GAT,.TRDEF,.SMF ;dcnlib definitions
	.MCALL	.PPKT,.GCLK,.GDAT,.TRAP,.PSEM,.VSEM ;dcnlib macros
	.MCALL	$DFIH,$DFTIM,$DFTBL ;moslib definitions
	.COM			;define common data
	.PSA			;define process storage areas
	.GAT			;define gateway/bridge storage areas
	.TRDEF			;define trap codes
	.SMF			;define semaphore ids
	$DFIH			;define internet header
	$DFTIM			;define timer values
	$DFTBL			;define host/gateway table formats
;
; Module definitions
;
TX.HLO	=	600.		;hello cache timeout (sec)
ETHDLY	=	12.		;delay estimate for broadcast nets (ms)
;
; Hello packet format
;
.	=	IH.LEN
LH.CHK:	.BLKW	1		;checksum
LH.DAT:	.BLKW	1		;current date
LH.TIM:	.BLKW	2		;current time of day
LH.TSP:	.BLKW	1		;timestamp of last hello msg
LH.TBL	=	.		;beginning of routing tables
LH.LEN:	.BLKB	1		;number of entries
LH.FMT:	.BLKB	1		;format identifier
LF.LCL	=	0		;local subnet
LF.FGN	=	1		;foreign subnet
	.PAGE
	.SBTTL	Hello message input processing
;
; Procedure segment
; Dsects: R3 = par, R5 = psa
;
; Process-state procedure
;
	.PSECT	$SUPI,RO,I
;
; Hello message input processing
;
; This section is called by the network-input process to update the host
; (routing) table. it uses the computed hello message roundtrip delay,
; together with the copy of the routing table transmitted by the other host,
; to determine the values of the delay, offset and pid entries.
;
; R3 = par pointer, R4 = packet pointer, R5 = psa pointer
;
NTIHLO:	CMP	PH.LNG(R4),#LH.TBL-IH.LEN ;verify format
	BHIS	1$		;branch if ok
	INC	PARFMT(R3)	;bad format
	RTS	PC
;
1$:	MOV	R4,R1		;verify checksum
	JSR	PC,DATSUM
	BEQ	2$		;branch if ok
	INC	PARCKS(R3)	;bad checksum
	RTS	PC
;
2$:	TSTB	PARSTX(R3)	;is link down
	BNE	3$		;branch if no
	BISB	PARSLB(R3),$ONLIN ;yes. declare up
	MOVB	PARIDX(R3),R0
	.TRAP	#TR.LUP,R0,IH.SRC(R4),IH.SRC+2(R4) ;link up
3$:	BISB	#1,PARSTX(R3)	;flag link up
	SWAB	LH.DAT(R4)	;swap byte fields
	SWAB	LH.TIM(R4)
	SWAB	LH.TIM+2(R4)
	SWAB	LH.TSP(R4)
	SUB	PH.TIM+2(R4),LH.TIM+2(R4) ;compute raw offset
	SBC	LH.TIM(R4)
	SUB	PH.TIM(R4),LH.TIM(R4)
	MOV	LH.TIM+2(R4),PARTSP(R3) ;save for timestamp
	MOV	PH.TIM+2(R4),R2	;compute delay
	SUB	LH.TSP(R4),R2
	BIT	#BSTBIT,PAROPT(R3) ;is this broadcast
	BEQ	4$		;branch if no
	MOV	#ETHDLY,R2	;yes. assume fixed (empirical) delay
	MOV	PH.LNG(R4),PARTFL(R3)
4$:	ADD	PARBIA(R3),R2	;correct for bias
	MOV	R2,R1		;correct offset
	SXT	R0
	ASR	R0
	ROR	R1
	SUB	PARBIA(R3),R1	;correct for bias
	SBC	R0
	ADD	R1,LH.TIM+2(R4)
	ADC	LH.TIM(R4)
	ADD	R0,LH.TIM(R4)
	MOV	IH.SRC(R4),R0	;copy source address to convenient place
	MOV	IH.SRC+2(R4),R1
	BIT	#DLXBIT,PAROPT(R3) ;is this tinkered delay
	BEQ	5$		;branch if no
	MOV	PARTRY(R3),R2	;yes. assume output timeout
5$:	CMP	R0,$NETID	;is this looped
	BNE	7$		;branch if no
	CMP	R1,$NETID+2
	BNE	7$		;branch if no
	ASR	R2		;yes. correct delay
	BIT	#GATBIT,PAROPT(R3) ;is this internal hello
	BNE	8$		;branch if yes
6$:	INC	PARMIS(R3)	;dropped (looped)
	RTS	PC
;
7$:	CMP	R0,PARADR(R3)	;is this a new neighbor
	BNE	10$		;branch if yes
	CMP	R1,PARADR+2(R3)
	BNE	10$		;branch if yes
8$:	BIT	#BSTBIT,PAROPT(R3) ;no. is this broadcast
	BNE	12$		;branch if yes
	TST	LH.TSP(R4)	;no. is delay valid
	BEQ	9$		;branch if no
	BITB	PARSLB(R3),$CKCNT
	BEQ	12$		;branch if yes
9$:	BISB	PARSLB(R3),$ROUTE ;no. encourage speed
	BR	6$
;
10$:	BIT	#GATBIT+BSTBIT,PAROPT(R3) ;new neighbor. is it a bogon
	BEQ	11$		;branch if no
	CMP	IH.DST(R4),PARADR(R3)
	BNE	6$		;branch if yes
	CMP	IH.DST+2(R4),PARADR+2(R3)
	BNE	6$		;branch if yes
	BR	12$		;no. cancel bogon alert
;
11$:	MOV	#TM.TTL,R2	;no bogon. assume infinite delay
	MOV	R0,PARADR(R3)	;save new address
	MOV	R1,PARADR+2(R3)
12$:	CMP	R2,#TM.MIN	;clip delay at lower limit
	BGE	13$
	MOV	#TM.MIN,R2
13$:	MOV	R2,LH.TSP(R4)
	BIT	#DWNBIT,PAROPT(R3) ;is routing disabled
	BNE	6$		;branch if yes
	ADD	#1,PARHLO+2(R3)	;tally hello messages received
	ADC	PARHLO(R3)
;
; Update routing table
;
; Note: lh.tsp(r4) = roundtrip delay
;	Lh.dat(r4) = date sent
;	Lh.tim(r4) = local clock offset (two words)
;	Ph.tim(r4) = time received (two words)
;	Lh.tbl(r4) = beginning of routing tables (also temp)
;
NTI20:	MOV	R4,R2		;point somewhere useful
	ADD	#LH.TBL,R2
	BIT	#GATBIT,PAROPT(R3) ;is this internal hello
	BEQ	1$		;branch if no
	CLR	(R2)+		;(lh.len,lh.fmt) yes. update destination
	MOV	#IH.DST,R1
	BR	9$
;
1$:	MOV	R4,R0		;external hello. is this end of update
	ADD	PH.OFS(R4),R0
	ADD	PH.LNG(R4),R0
	CMP	R2,R0
	BHIS	8$		;branch if yes
	MOV	(R2)+,LH.TBL(R4) ;(lh.len,lh.fmt)
	BEQ	8$		;branch if yes (pad)
	CMPB	LH.FMT(R4),#LF.FGN ;is this type-1 format
	BNE	4$		;branch if no
2$:	DECB	LH.LEN(R4)	;process next entry
	BMI	1$		;branch if done
	MOV	R2,R1
	CMP	(R2)+,(R2)+
	JSR	PC,ADRHLO	;update tables
3$:	CMP	(R2)+,(R2)+	;advance to next entry
	BR	2$
;
4$:	CMPB	LH.FMT(R4),#LF.LCL ;is this type-0 format
	BNE	8$		;branch if no (error)
	MOV	R4,R1		;yes. is source on same subnet
	ADD	#IH.SRC,R1
	JSR	PC,NETMAP
	BEQ	5$		;branch if yes
	MOVB	LH.LEN(R4),R0	;no. skip this table
	ASH	#2,R0
	ADD	R0,R2
	BR	1$
;
5$:	CLRB	LH.FMT(R4)	;type-0 format. update routing table
	MOV	#$HOSAD,R1
6$:	DECB	LH.LEN(R4)	;process next entry
	BMI	1$		;branch if done
	CMPB	LH.FMT(R4),$HOSAD-1
	BHIS	7$		;branch if out of range
	SWAB	@R2		;update routing table
	SWAB	2(R2)
	JSR	PC,UPDATE
7$:	ADD	#HOSLEN,R1	;advance to next entry
	CMP	(R2)+,(R2)+
	INCB	LH.FMT(R4)
	BR	6$
;
8$:	BIT	#SBNBIT,PAROPT(R3) ;is this subnet
	BEQ	10$		;branch if no
	MOV	#IH.SRC,R1	;yes. update source
9$:	ADD	R4,R1		;zero delay/offset (may use 32-bit trailer)
	CLR	@R2
	CLR	2(R2)
	JSR	PC,ADRHLO	;update tables
10$:	RTS	PC
	.PAGE
	.SBTTL	Hello message output processing
;
; Hello message output processing
;
; This section constructs and sends hello message to the host at the other end
; of this link including date, system clock, timestamp and host (routing)
; table.
;
; R3 = par pointer, R5 = psa pointer, returns c(cc) = 1 if no message needed
;
NTOHLO:	TSTB	PARSTX(R3)	;are hello messages enabled
	BNE	1$		;branch if yes
	BIT	#HLOBIT+GATBIT,PAROPT(R3)
	BEQ	5$		;branch if no
1$:	SUB	PARTRY(R3),HLOTIM(R5) ;yes. crank hello timeout
	BGT	2$		;branch if still running
	MOVB	PARMIN(R3),R0	;complete. reset timeout
	ASH	#10.-POLCON,R0	;(hello*1024.)
	MOV	R0,HLOTIM(R5)	
	BISB	PARSLB(R3),$ROUTE ;force hello
	CLC			;update link status
	ROLB	PARSTX(R3)
	BNE	2$		;branch if alive
	BCC	2$		;branch if dead
	BICB	PARSLB(R3),$ONLIN ;dying. declare down
	BICB	PARSLB(R3),$CKCNT
	BICB	PARSLB(R3),$ROUTE
	MOVB	PARIDX(R3),R0
	.TRAP	#TR.LDN,R0	;link down
2$:	TST	GATPTR(R5)	;is this first fragment
	BNE	4$		;branch if no
	BITB	PARSLB(R3),$CKCNT ;yes. has clock recently been reset
	BEQ	3$		;branch if no
	INC	HLDOFF(R5)	;yes. bump holdoff counter
	CMP	HLDOFF(R5),#2
	BLO	4$		;branch if still upright
	CLR	HLDOFF(R5)	;reset holdoff
	BICB	PARSLB(R3),$CKCNT
3$:	BITB	PARSLB(R3),$ROUTE
	BEQ	5$		;branch if no
	BICB	PARSLB(R3),$ROUTE
4$:	MOV	PARMAX(R3),R0	;allocate packet buffer
	.PPKT
	BNE	6$		;branch if ok
5$:	SEC			;no message needed
	RTS	PC
;
6$:	MOV	R0,R4		;save pointers
	MOV	R4,MSGDAT(R5)
	CLR	MSGIDN(R5)
	CLR	MSGIDM(R5)
	MOV	R4,R2		;initialize internet header
	ADD	#BUFLDR,R2
	MOV	#<P.IP*20+5>,(R2)+ ;(ih.ver, ih.tos)
	CLR	(R2)+		;(ih.fl)
	CLR	(R2)+		;(ih.id)
	MOV	#IH.DF,(R2)+	;(ih.frg) (don't fragment)
	MOV	#P.LNP*400+2+1,(R2)+ ;(ih.ttl, ih.pro) (ttl = 2 for bums)
	CLR	(R2)+		;(ih.chk)
	MOV	$NETID,(R2)+	;(ih.src)
	MOV	$NETID+2,(R2)+
	MOV	PARADR(R3),(R2)+ ;(ih.dst)
	MOV	PARADR+2(R3),(R2)+
	MOV	R2,PH.OFS(R4)	;save data offset
	SUB	R4,PH.OFS(R4)
	MOV	R4,R0		;construct default leader
	ADD	#PH.LDR,R0
	MOV	#377*400,(R0)+	;(ph.ldr)
	MOV	R0,R1
	MOV	PARADR(R3),(R0)+
	MOV	PARADR+2(R3),(R0)+
NTO17:	ADD	#LH.TBL-IH.LEN,R2 ;point to table area
	MOV	GATPTR(R5),R0	;is this later fragment
	BNE	NTO11		;branch if yes
	JSR	PC,NETMAP	;no. is this local subnet
	BNE	3$		;branch if no
	MOV	#$HOSAD-1,R1	;yes. construct type-0 table
	MOVB	(R1)+,R0
	MOVB	R0,(R2)+	;(lh.len)
	MOVB	#LF.LCL,(R2)+	;(lh.fmt)
1$:	DECB	R0		;is this end of table
	BMI	3$		;branch if yes
	MOV	HOSDLY(R1),@R2	;no. insert delay
	CMPB	PARPID(R3),HOSPID(R1) ;is this potential loop
	BNE	2$		;branch if no
	MOV	#TM.TTL,@R2	;yes. force max delay
2$:	SWAB	(R2)+
	MOV	HOSOFS(R1),@R2	;insert clock offset
	SWAB	(R2)+
	ADD	#HOSLEN,R1	;advance to next entry
	BR	1$
;
3$:	MOV	GATVPT,R0	;construct type-1 table
NTO11:	MOV	R2,R1
	MOV	#LF.FGN*400,(R2)+ ;(lh.len,lh.fmt)
	MOV	PARMAX(R3),-(SP) ;establish mtu bound
	ADD	#BUFLDR,@SP
	ADD	R4,@SP
1$:	BITB	#GT.HLO,GATFLG(R0) ;is net marked to send
	BEQ	8$		;branch if no
	BITB	#GT.CAC,GATFLG(R0) ;yes. is it alive
	BEQ	2$		;branch if yes
	TSTB	GATTTL(R0)
	BEQ	8$		;branch if no
2$:	ADD	#8.,R2		;is packet full
	CMP	R2,@SP
	BLOS	3$		;branch if no
	SUB	#8.,R2		;yes. resume sanity
	BR	10$
;
3$:	SUB	#8.,R2		;insert entry
	INCB	@R1		;(lh.len)
	MOV	R1,-(SP)	;juggle pointers
	MOV	GATNET(R0),(R2)+ ;insert net
	MOV	GATNET+2(R0),(R2)+
	CLR	R1		;is route wired
	BISB	GATHID(R0),R1
	BEQ	4$		;branch if yes
	CMPB	R1,$HOSAD-2
	BLO	5$		;branch if no
4$:	CLR	(R2)+		;yes. assume delay/offset zero
	CLR	(R2)+
	BR	7$
;
5$:	MUL	#HOSLEN,R1	;not wired. set pointer
	ADD	#$HOSAD,R1
	MOV	HOSDLY(R1),@R2	;insert delay
	CMPB	PARPID(R3),HOSPID(R1) ;is this potential loop
	BNE	6$		;branch if no
	TSTB	GATHOP(R0)
	BEQ	6$		;branch if no
	MOV	#TM.TTL,@R2	;yes. force max delay
6$:	SWAB	(R2)+
	MOV	HOSOFS(R1),@R2	;insert clock offset
	SWAB	(R2)+
7$:	MOV	(SP)+,R1
8$:	BITB	#GT.END,GATFLG(R0) ;is this end of table
	BNE	9$		;branch if yes
	ADD	#GATLEN,R0	;no. advance to next entry
	BR	1$
;
9$:	CLR	R0		;remember table pointer
	TST	GATPTR(R5)	;is this first fragment
	BEQ	11$		;branch if yes
10$:	CMP	R2,@SP		;no. pad to mtu bound
	BHIS	11$		;branch if done
	CLR	(R2)+		;paderewski
	BR	10$
;
11$:	MOV	R0,GATPTR(R5)	;save table pointer for later
	TST	(SP)+
	TSTB	@R1		;are there any entries
	BNE	12$		;branch if yes
	TST	-(R2)		;no. delete header
12$:	SUB	R4,R2		;save length for later
	SUB	PH.OFS(R4),R2
	MOV	R2,PARTFL(R3)
	MOV	R2,PH.LNG(R4)
NTO18:	.GDAT			;(lh.dat) insert date
	SWAB	R0
	MOV	R0,LH.DAT(R4)
	.GCLK			;(lh.tim) insert system clock
	MOV	R0,PH.TIM(R4)
	MOV	R1,PH.TIM+2(R4)
	SUB	PARBIA(R3),R1	;correct for bias
	SBC	R0
	SWAB	R0
	MOV	R0,LH.TIM(R4)
	MOV	R1,LH.TIM+2(R4)
	SWAB	LH.TIM+2(R4)
	ADD	PARTSP(R3),R1	;compute timestamp
	SUB	PARBIA(R3),R1	;correct for bias
	BITB	PARSLB(R3),$CKCNT ;is delay valid
	BNE	2$		;branch if no
	TSTB	PARSTX(R3)
	BNE	3$		;branch if yes
2$:	CLR	R1		;no. indicate that
3$:	SWAB	R1		;(lh.tsp)
	MOV	R1,LH.TSP(R4)
	CLR	LH.CHK(R4)	;compute checksum
	MOV	R4,R1
	JSR	PC,DATSUM
	MOV	R0,LH.CHK(R4)
	ADD	#1,PARHLX+2(R3)	;tally hello messages sent
	ADC	PARHLX(R3)
	CLC			;transmit packet
	RTS	PC
;
; Subroutine to update routing tables
; R1 = address pointer, r2 = update pointer, r4 = packet pointer
;
ADRHLO:	SWAB	@R2		;swap things
	SWAB	2(R2)
	JSR	PC,ADRPTR	;determine ip address mask
	MOV	2(R0),-(SP)	;save mask
	MOV	@R0,-(SP)
	MOV	2(R1),-(SP)	;save address
	MOV	@R1,-(SP)
	BIC	@R0,@SP		;mask address
	BIC	2(R0),2(SP)
	.PSEM	#SF.RUT		;lock routing tables
	MOV	SP,R1		;find entry
	JSR	PC,ADRMAP
	BCS	2$		;branch if not found
	BITB	#1,HOSLNA(R1)
	BNE	7$		;branch if multicast
	BITB	#GT.END,GATFLG(R0)
	BEQ	1$		;branch if not last
	TSTB	@SP
	BNE	2$		;branch if not default
1$:	BITB	#GT.ERR,GATFLG(R0)
	BNE	7$		;branch if egp default
	BITB	#GT.EGP,GATFLG(R0)
	BNE	4$		;branch if egp
	ADD	#10,SP		;update existing entry
	BR	9$
;
2$:	CMP	@R2,#TM.TTL	;not found. is host up
	BHIS	7$		;branch if no
	TSTB	@SP		;yes. is this default host
	BEQ	4$		;branch if yes
3$:	SUB	#GATLEN,R0	;no. back to previous entry
	BITB	#GT.CAC,GATFLG(R0) ;is this cache entry
	BEQ	7$		;branch if no
	TSTB	GATTTL(R0)	;yes. is it free
	BNE	3$		;branch if no
4$:	CLR	R1		;yes. find free hid
	BISB	$HOSAD-1,R1
	MOVB	R1,-(SP)
	MUL	#HOSLEN,R1
	ADD	#$HOSAD,R1
5$:	CMPB	@SP,$HOSAD-2	;is hid available
	BHIS	6$		;branch if no
	TSTB	HOSPID(R1)	;yes. is it free
	BEQ	8$		;branch if yes
	ADD	#HOSLEN,R1	;no. advance to next one
	INCB	@SP
	BR	5$
;
6$:	TSTB	(SP)+		;no hid available
7$:	ADD	#10,SP		;discard junk
	BR	11$
;
8$:	MOVB	(SP)+,GATHID(R0) ;found free hid. initialize net entry
	MOV	(SP)+,GATNET(R0)
	MOV	(SP)+,GATNET+2(R0)
	MOV	(SP)+,GATMSK(R0)
	MOV	(SP)+,GATMSK+2(R0)
	MOVB	#1,GATHOP(R0)	;*** primary route
	CLRB	HOSTTL(R1)
	MOV	#TM.TTL,HOSDLY(R1)
9$:	CMPB	GATHID(R0),$HOSAD-1 ;is this fixed area
	BLO	10$		;branch if yes
	BICB	#^C<GT.END>,GATFLG(R0) ;(take over from egp)
	BISB	#GT.HLO+GT.CAC,GATFLG(R0)
10$:	MOVB	GATHID(R0),LH.FMT(R4) ;(save for clock track) is entry wired
	BEQ	11$		;branch if yes
	CMPB	GATHID(R0),$HOSAD-2
	BHIS	11$		;branch if yes
	JSR	PC,UPDATE	;no. update routing table
11$:	.VSEM	#SF.RUT		;unlock routing tables
	RTS	PC
;
; Subroutine to update routing table entry
; lh.fmt = hid, r0 = net table pointer (type 1), r1 = routing table ptr,
; r2 = update ptr, r4 = packet ptr
;
UPDATE:	CMPB	LH.FMT(R4),$HOSAD-2 ;is this bogon
	BHIS	11$		;branch if yes
	BIT	#BSTBIT,PAROPT(R3) ;maybe not. is this tinkered delay
	BEQ	1$		;branch if no
	BIT	#DLXBIT,PAROPT(R3)
	BEQ	1$		;branch if no
	CLR	@R2		;yes. onward the zip
1$:	ADD	LH.TSP(R4),@R2	;compute delay/offset
	BVC	2$
	MOV	#100000+TM.TTL,@R2 ;clamp for overflow
2$:	CMPB	PARPID(R3),HOSPID(R1) ;is this the old way
	BNE	12$		;branch if no
	BIT	#GATBIT,PAROPT(R3)
	BNE	3$		;branch if yes
	CMPB	LH.FMT(R4),$HOSAD-1
	BLO	3$		;branch if yes
	CMP	IH.SRC(R4),GATLDR(R0)
	BNE	12$		;branch if no
	CMP	IH.SRC+2(R4),GATLDR+2(R0)
	BNE	12$		;branch if no
3$:	MOV	@R2,-(SP)	;yes. unsign delay
	BIC	#100000,@SP
	MOV	HOSDLY(R1),LH.CHK(R4) ;is new delay increasing too fast
	ASL	LH.CHK(R4)
	CMP	@R2,LH.CHK(R4)
	BHI	6$		;branch if yes
	ASR	LH.CHK(R4)	;no. is new delay decreasing too fast
	ASR	LH.CHK(R4)
	BIC	#140000,LH.CHK(R4)
	CMP	@R2,LH.CHK(R4)
	BHI	4$		;branch if no
	BISB	$ONLIN,$ROUTE	;yes. unlatch hold-down and flag for update
	BR	5$
;
4$:	CMP	HOSDLY(R1),#TM.TTL ;determine status
	BHIS	8$		;branch if hold-down or down
	BIT	#BSTBIT,PAROPT(R3) ;up. is this special hello
	BEQ	5$		;branch if no
	CMPB	LH.FMT(R4),$HOSAD-1
	BHIS	5$		;branch if no
	CMP	@SP,HOSDLY(R1)	;yes. keep min delay
	BLOS	5$
	MOV	HOSDLY(R1),@SP
5$:	MOV	(SP)+,@R2
	BR	15$
;
6$:	TSTB	HOSTTL(R1)	;increasing delay. determine status
	BEQ	10$		;branch if down
	CMP	HOSDLY(R1),#TM.TTL
	BHIS	8$		;branch if hold-down
	BIT	#BSTBIT,PAROPT(R3) ;up. is this special hello
	BEQ	7$		;branch if no
	CMPB	LH.FMT(R4),$HOSAD-1
	BLO	10$		;branch if yes
7$:	MOVB	#TS.LNK,HOSTTL(R1) ;no. latch hold-down and flag for update
	BISB	$ONLIN,$ROUTE
8$:	MOV	HOSDLY(R1),LH.CHK(R4) ;keep max delay
	BIC	#100000,LH.CHK(R4)
	CMP	@SP,LH.CHK(R4)
	BHIS	9$
	MOV	LH.CHK(R4),@SP
9$:	BIS	#100000,@SP	;flag hold-down
	MOV	(SP)+,HOSDLY(R1)
	RTS	PC
;
10$:	TST	(SP)+		;down. do not reset route
11$:	RTS	PC
;
12$:	CMP	@R2,#TM.TTL	;new way. is host reachable
	BHIS	11$		;branch if no
	TSTB	HOSTTL(R1)	;yes. determine status
	BEQ	13$		;branch if down
	CMP	HOSDLY(R1),#TM.TTL
	BHIS	11$		;branch if hold-down
13$:	MOV	HOSDLY(R1),-(SP) ;host up or down. is new way shorter
	ASR	@SP		;(constant 0.75)
	ASR	@SP
	NEG	@SP
	ADD	HOSDLY(R1),@SP
	CMP	@R2,(SP)+
	BHI	11$		;branch if no
	CMPB	LH.FMT(R4),$HOSAD-1
	BLO	14$		;branch if not type-1
	INC	$RTCHG		;log route change
	CMP	GATNET(R0),$TRNET ;is this traced net
	BNE	14$		;branch if no
	CMP	GATNET+2(R0),$TRNET+2
	BNE	14$		;branch if no
	INC	$RTCHG+2	;yes. log traced route change
	MOV	R0,-(SP)
	MOV	R1,-(SP)
	MOVB	PARIDX(R3),R1
	.TRAP	#TR.RUT,GATNET(R0),GATNET+2(R0),R1,@R2
	MOV	(SP)+,R1
	MOV	(SP)+,R0
14$:	MOVB	PARPID(R3),HOSPID(R1) ;reset route
	CLR	HOSOFS(R1)
	CLR	HOSLNA(R1)
	CLR	HOSLNA+2(R1)
	CLR	HOSLNA+4(R1)
	BISB	$ONLIN,$ROUTE	;flag for update
15$:	CMPB	LH.FMT(R4),$HOSAD-1 ;is this type 1
	BLO	16$		;branch if no
	MOVB	#TX.HLO/30.,GATTTL(R0) ;yes. tickle ttl
	CLR	GATLDR(R0)	;is this internal hello
	CLR	GATLDR+2(R0)
	BIT	#GATBIT,PAROPT(R3)
	BNE	16$		;branch if yes
	MOV	IH.SRC(R4),GATLDR(R0) ;no. stash ip source address
	MOV	IH.SRC+2(R4),GATLDR+2(R0)
16$:	MOV	LH.DAT(R4),R0	;is clock synchronized
	COM	R0
	BIT	#140000,R0
	BEQ	17$		;branch if no
	ADD	LH.TIM+2(R4),2(R2) ;yes. update offset
	CMPB	LH.FMT(R4),$CKHID ;is clock primed to this host
	BNE	17$		;branch if no
	CMP	PH.LNG(R4),PARTFL(R3)
	BNE	17$		;branch if no
	CLR	PARTFL(R3)	;yes. update local clock
	.TRAP	#TR.CLK,#0*400+CK.DCN,@R2,LH.DAT(R4),LH.TIM(R4),LH.TIM+2(R4)
17$:	MOV	@R2,HOSDLY(R1)	;update routing table
	MOV	2(R2),HOSOFS(R1)
	MOVB	PARMIN(R3),R0
	ASH	#2,R0
	MOVB	R0,HOSTTL(R1) 
	MOV	PH.TIM(R4),HOSTIM(R1)
	MOV	PH.TIM+2(R4),HOSTIM+2(R1)
	RTS	PC
;
; Netest (rut) test neighbor net
; R1 = internet address (word) pointer, returns cc(z) = 1 if neighbor net
;
NETEST:	JSR	PC,ADRPTR	;get address mask
	BNE	1$		;branch if different subnet
	MOV	#$NETID+4,R0	;same subnet. use subnet mask
1$:	MOV	@R1,-(SP)	;is address on same neighbor net
	BIC	@R0,@SP
	MOV	PARADR(R3),-(SP)
	BIC	(R0)+,@SP
	CMP	(SP)+,(SP)+
	BNE	2$		;branch if no
	MOV	2(R1),-(SP)
	BIC	@R0,@SP
	MOV	PARADR+2(R3),-(SP)
	BIC	(R0)+,@SP
	CMP	(SP)+,(SP)+
2$:	RTS	PC		;return cc(z) = 1 if neighbor net
;
; Subroutine to determine ip address mask
; R1 = internet address pointer, returns r0 = mask pointer,
; cc(z) = 1 if home subnet
;	
ADRPTR:	MOV	#MSKTAB,R0	;determine address class
	TSTB	@R1
	BEQ	2$		;branch if default
	CMP	(R0)+,(R0)+
	JSR	PC,NETMAP
	BEQ	3$		;branch if same subnet
	CMP	(R0)+,(R0)+
	CMPB	@R1,#128.	
	BLO	1$		;branch if class a
	CMP	(R0)+,(R0)+
	CMPB	@R1,#192.
	BLO	1$		;branch if class b
	CMP	(R0)+,(R0)+	;class c
1$:	MOV	@R1,-(SP)	;is address on same ip net
	BIC	@R0,@SP
	MOV	$NETID,-(SP)
	BIC	@R0,@SP
	CMP	(SP)+,(SP)+
	BNE	3$		;branch if no
	MOV	2(R1),-(SP)
	BIC	2(R0),@SP
	MOV	$NETID+2,-(SP)
	BIC	2(R0),@SP
	CMP	(SP)+,(SP)+
	BNE	3$		;branch if no
	MOV	#$NETID+4,R0	;yes. use subnet mask
2$:	CLZ
3$:	RTS	PC		;cc(z) = 1 if home subnet
;
	.PSECT	$SUPD,RO,D	;supervisor d-space
;
; IP mask table
;
MSKTAB:	.BYTE	377,377,377,377	;default
	.BYTE	000,000,000,000	;same subnet
	.BYTE	000,377,377,377	;class a
	.BYTE	000,000,377,377	;class b
	.BYTE	000,000,000,377	;class c
	.EVEN
;
	.END