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Annotation of 43BSDTahoe/man/man4/vax/ec.4, revision 1.1.1.1

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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