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1.1 root 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: .\"
5: .\" @(#)en.4 6.2 (Berkeley) 5/16/86
6: .\"
7: .TH EN 4 "May 16, 1986"
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
19: of the UNIBUS address space, and thus this must be among the first
20: UNIBUS devices enabled after boot.
21: .PP
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.
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
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
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.
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