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Annotation of 43BSDTahoe/man/man4/vax/ec.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: .\"    @(#)ec.4        6.4 (Berkeley) 5/16/86
        !             6: .\"
        !             7: .TH EC 4 "May 16, 1986"
        !             8: .UC 5
        !             9: .SH NAME
        !            10: ec \- 3Com 10 Mb/s Ethernet interface
        !            11: .SH SYNOPSIS
        !            12: .B "device ec0 at uba0 csr 161000 vector ecrint eccollide ecxint flags 0"
        !            13: .SH DESCRIPTION
        !            14: The
        !            15: .I ec
        !            16: interface provides access to a 10 Mb/s Ethernet network through
        !            17: a 3com controller.
        !            18: .PP
        !            19: The hardware has 32 kilobytes of dual-ported memory on the UNIBUS. 
        !            20: This memory
        !            21: is used for internal buffering by the board, and the interface code reads
        !            22: the buffer contents directly through the UNIBUS.
        !            23: The address of this memory is given in the \fIflags\fP field
        !            24: in the configuration file.
        !            25: The first interface normally has its memory at Unibus address 0.
        !            26: .PP
        !            27: Each of the host's network addresses
        !            28: is specified at boot time with an SIOCSIFADDR
        !            29: ioctl.  The
        !            30: .I ec
        !            31: interface employs the address resolution protocol described in
        !            32: .IR arp (4P)
        !            33: to dynamically map between Internet and Ethernet addresses on the local
        !            34: network.
        !            35: .PP
        !            36: The interface normally tries to use a ``trailer'' encapsulation
        !            37: to minimize copying data on input and output.
        !            38: The use of trailers is negotiated with ARP.
        !            39: This negotiation may be disabled, on a per-interface basis,
        !            40: by setting the IFF_NOTRAILERS
        !            41: flag with an SIOCSIFFLAGS ioctl.
        !            42: .PP
        !            43: The interface software implements an exponential backoff algorithm
        !            44: when notified of a collision on the cable.  This algorithm utilizes
        !            45: a 16-bit mask and the VAX-11's interval timer in calculating a series
        !            46: of random backoff values.  The algorithm is as follows:
        !            47: .TP 5
        !            48: 1.
        !            49: Initialize the mask to be all 1's.
        !            50: .TP 5
        !            51: 2.
        !            52: If the mask is zero, 16 retries have been made and we give
        !            53: up.
        !            54: .TP 5
        !            55: 3.
        !            56: Shift the mask left one bit and formulate a backoff by
        !            57: masking the interval timer with the smaller of the complement of this mask
        !            58: and a 5-bit mask, resulting in a pseudo-random number between 0 and 31.
        !            59: This produces the number of slot times to delay,
        !            60: where a slot is 51 microseconds.
        !            61: .TP 5
        !            62: 4.
        !            63: Use the value calculated in step 3 to delay before retransmitting
        !            64: the packet.
        !            65: The delay is done in a software busy loop.
        !            66: .SH DIAGNOSTICS
        !            67: .BR "ec%d: send error" .
        !            68: After 16 retransmissions using the
        !            69: exponential backoff algorithm described above, the packet
        !            70: was dropped.
        !            71: .PP
        !            72: .BR "ec%d: input error (offset=%d)" .
        !            73: The hardware indicated an error
        !            74: in reading a packet off the cable or an illegally sized packet.
        !            75: The buffer offset value is printed for debugging purposes.
        !            76: .PP
        !            77: .BR "ec%d: can't handle af%d" .
        !            78: The interface was handed
        !            79: a message with addresses formatted in an unsuitable address
        !            80: family; the packet was dropped.
        !            81: .SH SEE ALSO
        !            82: intro(4N), inet(4F), arp(4P)
        !            83: .SH BUGS
        !            84: The hardware is not capable of talking to itself.  The software
        !            85: implements local sending and broadcast by sending such packets to the
        !            86: loop interface.  This is a kludge.
        !            87: .PP
        !            88: Backoff delays are done in a software busy loop.  This can degrade the
        !            89: system if the network experiences frequent collisions.

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