[unix-history] / usr / man / man4 / en.4

.TH EN 4 "27 July 1983"
.UC 4
.SH NAME
en \- Xerox 3 Mb/s Ethernet interface
.SH SYNOPSIS
.B "device en0 at uba0 csr 161000 vector enrint enxint encollide"
.SH DESCRIPTION
The
.I en
interface provides access to a 3 Mb/s Ethernet network.
Due to limitations in the hardware, DMA transfers
to and from the network must take place in the lower 64K bytes
of the UNIBUS address space.
.PP
The network number is specified with a SIOCSIFADDR ioctl; the
host's address is discovered by probing the on-board Ethernet
address register.  No packets will be sent or accepted until 
a network number is supplied.
.PP
The interface software implements an exponential backoff algorithm
when notified of a collision on the cable.  This algorithm utilizes
a 16-bit mask and the VAX-11's interval timer in calculating a series
of random backoff values.  The algorithm is as follows:
.TP 5
1.
Initialize the mask to be all 1's.
.TP 5
2.
If the mask is zero, 16 retries have been made and we give
up.
.TP 5
3.
Shift the mask left one bit and formulate a backoff by
masking the interval timer with the mask (this is actually
the two's complement of the value).
.TP 5
4.
Use the value calculated in step 3 to delay before retransmitting
the packet.
.PP
The interface handles both Internet and PUP protocol families,
with the interface address maintained in Internet format.
PUP addresses are converted to Internet addresses by subsituting
PUP network and host values for Internet network and local part
values.
.PP
The interface normally tries to use a ``trailer'' encapsulation
to minimize copying data on input and output.  This may be
disabled, on a per-interface basis, by setting the IFF_NOTRAILERS
flag with an SIOCSIFFLAGS ioctl.
.SH DIAGNOSTICS
.BR "en%d: output error" .
The hardware indicated an error on
the previous transmission.
.PP
.BR "en%d: send error" .
After 16 retransmissions using the
exponential backoff algorithm described above, the packet
was dropped.
.PP
.BR "en%d: input error" .
The hardware indicated an error
in reading a packet off the cable.
.PP
.BR "en%d: can't handle af%d" .
The interface was handed
a message with addresses formatted in an unsuitable address
family; the packet was dropped.
.SH SEE ALSO
intro(4N), inet(4F)
.SH BUGS
The device has insufficient buffering to handle back to
back packets.  This makes use in a production environment
painful.
.PP
The hardware does word at a time DMA without byte swapping.
To compensate, byte swapping of user data must either be done 
by the user or by the system.  A kludge to byte swap only
IP packets is provided if the ENF_SWABIPS flag is defined in
the driver and set at boot time with an SIOCSIFFLAGS ioctl.
Commit	Line	Data
673b0044 C	1	.TH EN 4 "27 July 1983"
	2	.UC 4
	3	.SH NAME
	4	en \- Xerox 3 Mb/s Ethernet interface
	5	.SH SYNOPSIS
	6	.B "device en0 at uba0 csr 161000 vector enrint enxint encollide"
	7	.SH DESCRIPTION
	8	The
	9	.I en
	10	interface provides access to a 3 Mb/s Ethernet network.
	11	Due to limitations in the hardware, DMA transfers
	12	to and from the network must take place in the lower 64K bytes
	13	of the UNIBUS address space.
	14	.PP
	15	The network number is specified with a SIOCSIFADDR ioctl; the
	16	host's address is discovered by probing the on-board Ethernet
	17	address register. No packets will be sent or accepted until
	18	a network number is supplied.
	19	.PP
	20	The interface software implements an exponential backoff algorithm
	21	when notified of a collision on the cable. This algorithm utilizes
	22	a 16-bit mask and the VAX-11's interval timer in calculating a series
	23	of random backoff values. The algorithm is as follows:
	24	.TP 5
	25	1.
	26	Initialize the mask to be all 1's.
	27	.TP 5
	28	2.
	29	If the mask is zero, 16 retries have been made and we give
	30	up.
	31	.TP 5
	32	3.
	33	Shift the mask left one bit and formulate a backoff by
	34	masking the interval timer with the mask (this is actually
	35	the two's complement of the value).
	36	.TP 5
	37	4.
	38	Use the value calculated in step 3 to delay before retransmitting
	39	the packet.
	40	.PP
	41	The interface handles both Internet and PUP protocol families,
	42	with the interface address maintained in Internet format.
	43	PUP addresses are converted to Internet addresses by subsituting
	44	PUP network and host values for Internet network and local part
	45	values.
	46	.PP
	47	The interface normally tries to use a ``trailer'' encapsulation
	48	to minimize copying data on input and output. This may be
	49	disabled, on a per-interface basis, by setting the IFF_NOTRAILERS
	50	flag with an SIOCSIFFLAGS ioctl.
	51	.SH DIAGNOSTICS
	52	.BR "en%d: output error" .
	53	The hardware indicated an error on
	54	the previous transmission.
	55	.PP
	56	.BR "en%d: send error" .
	57	After 16 retransmissions using the
	58	exponential backoff algorithm described above, the packet
	59	was dropped.
	60	.PP
	61	.BR "en%d: input error" .
	62	The hardware indicated an error
	63	in reading a packet off the cable.
	64	.PP
65	.BR "en%d: can't handle af%d" .
66	The interface was handed
67	a message with addresses formatted in an unsuitable address
68	family; the packet was dropped.
69	.SH SEE ALSO
70	intro(4N), inet(4F)
71	.SH BUGS
72	The device has insufficient buffering to handle back to
73	back packets. This makes use in a production environment
74	painful.
75	.PP
76	The hardware does word at a time DMA without byte swapping.
77	To compensate, byte swapping of user data must either be done
78	by the user or by the system. A kludge to byte swap only
79	IP packets is provided if the ENF_SWABIPS flag is defined in
80	the driver and set at boot time with an SIOCSIFFLAGS ioctl.