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

.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)en.4	6.2 (Berkeley) 5/16/86
.\"
.TH EN 4 "May 16, 1986"
.UC 5
.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, and thus this must be among the first
UNIBUS devices enabled after boot.
.PP
Each of the host's network addresses
is specified at boot time with an SIOCSIFADDR
ioctl.  The station address is discovered by probing the on-board Ethernet
address register, and is used to verify the protocol addresses.
No packets will be sent or accepted until 
a network address 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 NS protocol families.
It normally tries to use a ``trailer'' encapsulation
to minimize copying data on input and output.
The use of trailers is negotiated with ARP.
This negotiation 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
6ec15d08 KM	1	.\" Copyright (c) 1983 Regents of the University of California.
	2	.\" All rights reserved. The Berkeley software License Agreement
	3	.\" specifies the terms and conditions for redistribution.
	4	.\"
95f51977	5	.\" @(#)en.4 6.2 (Berkeley) 5/16/86
6ec15d08	6	.\"
95f51977	7	.TH EN 4 "May 16, 1986"
6ec15d08 KM	8	.UC 5
	9	.SH NAME
	10	en \- Xerox 3 Mb/s Ethernet interface
	11	.SH SYNOPSIS
	12	.B "device en0 at uba0 csr 161000 vector enrint enxint encollide"
	13	.SH DESCRIPTION
	14	The
	15	.I en
	16	interface provides access to a 3 Mb/s Ethernet network.
	17	Due to limitations in the hardware, DMA transfers
	18	to and from the network must take place in the lower 64K bytes
f183d20a MK	19	of the UNIBUS address space, and thus this must be among the first
f183d20a MK	20	UNIBUS devices enabled after boot.
6ec15d08	21	.PP
f183d20a MK	22	Each of the host's network addresses
	23	is specified at boot time with an SIOCSIFADDR
	24	ioctl. The station address is discovered by probing the on-board Ethernet
	25	address register, and is used to verify the protocol addresses.
	26	No packets will be sent or accepted until
	27	a network address is supplied.
6ec15d08 KM	28	.PP
	29	The interface software implements an exponential backoff algorithm
	30	when notified of a collision on the cable. This algorithm utilizes
	31	a 16-bit mask and the VAX-11's interval timer in calculating a series
	32	of random backoff values. The algorithm is as follows:
	33	.TP 5
	34	1.
	35	Initialize the mask to be all 1's.
	36	.TP 5
	37	2.
	38	If the mask is zero, 16 retries have been made and we give
	39	up.
	40	.TP 5
	41	3.
	42	Shift the mask left one bit and formulate a backoff by
	43	masking the interval timer with the mask (this is actually
	44	the two's complement of the value).
	45	.TP 5
	46	4.
	47	Use the value calculated in step 3 to delay before retransmitting
	48	the packet.
	49	.PP
f183d20a MK	50	The interface handles both Internet and NS protocol families.
	51	It normally tries to use a ``trailer'' encapsulation
	52	to minimize copying data on input and output.
	53	The use of trailers is negotiated with ARP.
	54	This negotiation may be disabled, on a per-interface basis,
	55	by setting the IFF_NOTRAILERS
6ec15d08 KM	56	flag with an SIOCSIFFLAGS ioctl.
	57	.SH DIAGNOSTICS
	58	.BR "en%d: output error" .
	59	The hardware indicated an error on
	60	the previous transmission.
	61	.PP
	62	.BR "en%d: send error" .
	63	After 16 retransmissions using the
	64	exponential backoff algorithm described above, the packet
	65	was dropped.
	66	.PP
	67	.BR "en%d: input error" .
	68	The hardware indicated an error
	69	in reading a packet off the cable.
	70	.PP
	71	.BR "en%d: can't handle af%d" .
	72	The interface was handed
	73	a message with addresses formatted in an unsuitable address
	74	family; the packet was dropped.
	75	.SH SEE ALSO
	76	intro(4N), inet(4F)
	77	.SH BUGS
	78	The device has insufficient buffering to handle back to
	79	back packets. This makes use in a production environment
	80	painful.
	81	.PP
	82	The hardware does word at a time DMA without byte swapping.
	83	To compensate, byte swapping of user data must either be done
	84	by the user or by the system. A kludge to byte swap only
	85	IP packets is provided if the ENF_SWABIPS flag is defined in
	86	the driver and set at boot time with an SIOCSIFFLAGS ioctl.