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Annotation of 43BSDTahoe/man/man4/vax/en.4, revision 1.1

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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