312 lines
9.9 KiB
Groff
312 lines
9.9 KiB
Groff
.\" $NetBSD: plip.4,v 1.3 2009/03/09 19:24:28 joerg Exp $
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.\"
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.\" Copyright (c) 1996 A.R.Gordon, andrew.gordon@net-tel.co.uk
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" Id: man4.i386/lp.4,v 1.9 1999/02/14 12:06:16 nsouch Exp
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.\" $FreeBSD: src/share/man/man4/lp.4,v 1.5.2.3 2000/12/29 10:18:00 ru Exp $
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.\"
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.Dd January 28, 2004
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.Dt PLIP 4
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.Os
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.Sh NAME
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.Nm plip
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.Nd printer port Internet Protocol driver
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.Sh SYNOPSIS
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.Cd "plip* at ppbus?"
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.Cd options PLIP_DEBUG
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.Sh DESCRIPTION
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The
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.Nm
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driver allows a PC parallel printer port to be used as a point-to-point
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network interface between two similarly configured systems.
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Data is transferred 4 bits at a time, using the printer status
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lines for input: hence there is no requirement for special
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bidirectional hardware and any standard AT-compatible printer port
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with working interrupts may be used.
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.Pp
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During the boot process, for each
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.Xr ppbus 4
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device which is attached and has an interrupt capability, a
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corresponding
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.Nm
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device is attached.
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The
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.Nm
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device is configured using
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.Xr ifconfig 8
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using the options for a point-to-point network interface:
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.Pp
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.Nm ifconfig
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.Ar plip0
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.Ar hostaddress destaddress
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.Op Fl link0|link0
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.Op up|down
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.Op ...
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.Pp
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Configuring a
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.Nm
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device
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.Dq up
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with
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.Xr ifconfig 8
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causes the corresponding
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.Xr ppbus 4
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to be reserved for PLIP until the network interface is configured
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.Dq down .
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.Pp
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The communication protocol is selected by the
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.Cm link0
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flag:
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.Bl -tag -width Fl
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.It Fl link0
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(default)
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Use
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.Fx
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mode (LPIP).
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This is the simpler of the two modes and therefore slightly more
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efficient.
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.It Cm link0
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Use Crynwr/Linux compatible mode (CLPIP).
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This mode has a simulated ethernet packet header, and is easier to
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interface to other types of equipment.
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.El
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.Pp
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The interface MTU defaults to 1500, but may be set to any value.
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Both ends of the link must be configured with the same MTU.
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See
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.Xr ifconfig 8
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for details on configuring network interfaces.
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.Ss Cable Connections
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The cable connecting the two parallel ports should be wired as follows:
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.Bd -literal
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Pin Pin Description
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2 15 Data0 -\*[Gt] ERROR*
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3 13 Data1 -\*[Gt] SLCT
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4 12 Data2 -\*[Gt] PE
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5 10 Data3 -\*[Gt] ACK*
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6 11 Data4 -\*[Gt] BUSY
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15 2 ERROR* -\*[Gt] Data0
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13 3 SLCT -\*[Gt] Data1
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12 4 PE -\*[Gt] Data2
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10 5 ACK* -\*[Gt] Data3
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11 6 BUSY -\*[Gt] Data4
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18-25 18-25 Ground
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.Ed
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.Pp
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Cables with this wiring are widely available as
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.Dq Tn Laplink
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cables, and are often colored yellow.
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.Pp
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The connections are symmetric, and provide 5 lines in each direction
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(four data plus one handshake).
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The two modes use the same wiring, but make a
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different choice of which line to use as handshake.
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.Ss FreeBSD LPIP mode
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The signal lines are used as follows:
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.Bl -tag -width dataxxxxXPinxxX
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.It Em Data0 (Pin 2)
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Data out, bit 0.
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.It Em Data1 (Pin 3)
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Data out, bit 1.
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.It Em Data2 (Pin 4)
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Data out, bit 2.
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.It Em Data3 (Pin 5)
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Handshake out.
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.It Em Data4 (Pin 6)
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Data out, bit 3.
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.It Em ERROR* (pin 15)
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Data in, bit 0.
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.It Em SLCT (pin 13)
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Data in, bit 1.
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.It Em PE (pin 12)
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Data in, bit 2.
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.It Em BUSY (pin 11)
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Data in, bit 3.
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.It Em ACK* (pin 10)
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Handshake in.
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.El
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.Pp
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When idle, all data lines are at zero.
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Each byte is signaled in four steps: sender writes the 4 most
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significant bits and raises the handshake line; receiver reads the
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4 bits and raises its handshake to acknowledge; sender places the
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4 least significant bits on the data lines and lowers the handshake;
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receiver reads the data and lowers its handshake.
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.Pp
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The packet format has a two-byte header, comprising the fixed values
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0x08, 0x00, immediately followed by the IP header and data.
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.Pp
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The start of a packet is indicated by simply signaling the first
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byte of the header.
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The end of the packet is indicated by inverting the data lines
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(i.e. writing the ones-complement of the previous nibble to be
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transmitted) without changing the state of the handshake.
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.Pp
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Note that the end-of-packet marker assumes that the handshake signal
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and the data-out bits can be written in a single instruction -
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otherwise certain byte values in the packet data would falsely be
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interpreted as end-of-packet.
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This is not a problem for the PC printer port, but requires care
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when implementing this protocol on other equipment.
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.Ss Crynwr/Linux CLPIP mode
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The signal lines are used as follows:
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.Bl -tag -width dataxxxxXPinxxX
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.It Em Data0 (Pin 2)
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Data out, bit 0.
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.It Em Data1 (Pin 3)
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Data out, bit 1.
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.It Em Data2 (Pin 4)
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Data out, bit 2.
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.It Em Data3 (Pin 5)
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Data out, bit 3.
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.It Em Data4 (Pin 6)
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Handshake out.
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.It Em ERROR* (pin 15)
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Data in, bit 0.
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.It Em SLCT (pin 13)
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Data in, bit 1.
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.It Em PE (pin 12)
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Data in, bit 2.
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.It Em ACK* (pin 10)
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Data in, bit 3.
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.It Em BUSY (pin 11)
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Handshake in.
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.El
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.Pp
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When idle, all data lines are at zero.
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Each byte is signaled in four steps: sender writes the 4 least
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significant bits and raises the handshake line; receiver reads the
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4 bits and raises its handshake to acknowledge; sender places the
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4 most significant bits on the data lines and lowers the handshake;
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receiver reads the data and lowers its handshake.
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[Note that this is the opposite nibble order to LPIP mode].
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.Pp
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Packet format is:
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.Bd -literal
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Length (least significant byte)
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Length (most significant byte)
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12 bytes of supposed MAC addresses (ignored by FreeBSD).
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Fixed byte 0x08
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Fixed byte 0x00
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\*[Lt]IP datagram\*[Gt]
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Checksum byte.
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.Ed
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.Pp
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The length includes the 14 header bytes, but not the length bytes
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themselves nor the checksum byte.
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.Pp
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The checksum is a simple arithmetic sum of all the bytes (again,
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including the header but not checksum or length bytes).
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.Fx
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calculates outgoing checksums, but does not validate incoming ones.
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.Pp
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The start of packet has to be signaled specially, since the line
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chosen for handshake-in cannot be used to generate an interrupt.
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The sender writes the value 0x08 to the data lines, and waits for
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the receiver to respond by writing 0x01 to its data lines.
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The sender then starts signaling the first byte of the packet (the
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length byte).
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.Pp
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End of packet is deduced from the packet length and is not signaled
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specially (although the data lines are restored to the zero, idle
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state to avoid spuriously indicating the start of the next packet).
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.Sh SEE ALSO
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.Xr atppc 4 ,
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.Xr ppbus 4 ,
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.Xr ifconfig 8
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.Sh HISTORY
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The
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.Nm
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driver was implemented for
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.Xr ppbus 4
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in
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.Fx
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and imported into
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.Nx .
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Crynwr packet drivers implemented PLIP for
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.Tn MS-DOS .
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Linux also has a PLIP driver.
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The protocols are know as LPIP
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.Pq Fx
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and CLPIP (Crynwr/Linux) in the documentation and code of this
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port.
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LPIP originally appeared in
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.Fx .
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.Sh AUTHORS
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This manual page is based on the
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.Fx
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.Nm lp
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manual page.
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The information has been updated for the
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.Nx
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port by Gary Thorpe.
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.Sh BUGS
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Busy-waiting loops are used while handshaking bytes (and worse
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still when waiting for the receiving system to respond to an
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interrupt for the start of a packet).
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Hence a fast system talking to a slow one will consume excessive
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amounts of CPU.
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This is unavoidable in the case of CLPIP mode due to the choice of
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handshake lines; it could theoretically be improved in the case of
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LPIP mode.
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.Pp
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Regardless of the speed difference between hosts, PLIP is CPU-intensive
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and its made worse by having to send nibbles (4 bits) at a time.
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.Pp
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Polling timeouts are controlled by counting loop iterations rather
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than timers, and so are dependent on CPU speed.
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This is somewhat stabilized by the need to perform (slow) ISA bus
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cycles to actually read the port.
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.Pp
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In the
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.Fx
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implementation, the idle state was not properly being restored on
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errors or when finishing transmitting/receiving.
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This implementation attempts to fix this problem which would result
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in an unresponsive interface that could no longer be used (the port
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bits get stuck in a state and nothing can progress) by zeroing the
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data register when necessary.
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.Pp
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For unknown reasons, the more complex protocol (CLPIP) yields higher
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data transfer rates during testing so far.
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This could possibly be because the other side can reliably detect
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when the host is transmitting in this implementation of CLPIP (this
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may not necessarily be true in Linux or
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.Tn MS-DOS
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packet drivers).
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CLPIP gets about 70 KB/sec (the best expected is about 75 KB/sec)
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and LPIP get about 55 KB/sec.
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This is despite LPIP being able to send more packets over the
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interface (tested with
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.Dq Ic ping Fl f )
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compared to CLPIP.
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