1.\" -*- nroff -*- 2.\" 3.\" Copyright (c) 1996 A.R.Gordon, andrew.gordon@net-tel.co.uk 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" Id: man4.i386/lp.4,v 1.9 1999/02/14 12:06:16 nsouch Exp 35.\" $FreeBSD$ 36.\" 37.Dd March 4, 1996 38.Os 39.Dt LP 4 40.Sh NAME 41.Nm lp 42.Nd printer port Internet Protocol driver 43.Sh SYNOPSIS 44.Nm ifconfig 45.Ar plip0 46.Ar myaddress hisaddress 47.Op Fl link0 48.Pp 49.Cd "device ppbus" 50.Cd "device plip" 51.Cd "device ppc" 52.Sh DESCRIPTION 53The 54.Nm 55driver allows a PC parallel printer port to be used as a 56point-to-point network interface between two similarly configured systems. 57Data is transferred 4 bits at a time, using the printer status lines for 58input: hence there is no requirement for special bidirectional hardware 59and any standard AT-compatible printer port with working interrupts may be used. 60.Pp 61During the boot process, for each 62.Nm plip 63device which is probed and has an interrupt assigned, a corresponding 64.Nm network 65device is created. 66.Pp 67Configuring an 68.Nm 69device with 70.Xr ifconfig 8 71causes the corresponding 72.Nm parallel port bus 73to be reserved for PLIP until the network interface is configured 'down'. 74.Pp 75The communication protocol is selected by the 76.Cm link0 77flag: 78.Bl -tag -width Fl 79.It Fl link0 80(default) Use 81.Fx 82mode (LPIP). 83This is the simpler of the two modes 84and therefore slightly more efficient. 85.It Cm link0 86Use Crynwr/Linux compatible mode (CLPIP). 87This mode has a simulated Ethernet 88packet header, and is easier to interface to other types of equipment. 89.El 90.Pp 91The interface MTU defaults to 1500, but may be set to any value. 92Both ends 93of the link must be configured with the same MTU. 94.Ss Cable Connections 95The cable connecting the two parallel ports should be wired as follows: 96.Bd -literal 97 Pin Pin Description 98 2 15 Data0 -> ERROR* 99 3 13 Data1 -> SLCT 100 4 12 Data2 -> PE 101 5 10 Data3 -> ACK* 102 6 11 Data4 -> BUSY 103 15 2 ERROR* -> Data0 104 13 3 SLCT -> Data1 105 12 4 PE -> Data2 106 10 5 ACK* -> Data3 107 11 6 BUSY -> Data4 108 18-25 18-25 Ground 109.Ed 110.Pp 111Cables with this wiring are widely available as 'Laplink' cables, and 112are often coloured yellow. 113.Pp 114The connections are symmetric, and provide 5 lines in each direction (four 115data plus one handshake). 116The two modes use the same wiring, but make a 117different choice of which line to use as handshake. 118.Ss FreeBSD LPIP mode 119The signal lines are used as follows: 120.Bl -tag -width dataxxxx(Pinxx) 121.It Em Data0 (Pin 2) 122Data out, bit 0. 123.It Em Data1 (Pin 3) 124Data out, bit 1. 125.It Em Data2 (Pin 4) 126Data out, bit 2. 127.It Em Data3 (Pin 5) 128Handshake out. 129.It Em Data4 (Pin 6) 130Data out, bit 3. 131.It Em ERROR* (pin 15) 132Data in, bit 0. 133.It Em SLCT (pin 13) 134Data in, bit 1. 135.It Em PE (pin 12) 136Data in, bit 2. 137.It Em BUSY (pin 11) 138Data in, bit 3. 139.It Em ACK* (pin 10) 140Handshake in. 141.El 142.Pp 143When idle, all data lines are at zero. 144Each byte is signalled in four steps: 145sender writes the 4 most significant bits and raises the handshake line; 146receiver reads the 4 bits and raises its handshake to acknowledge; 147sender places the 4 least significant bits on the data lines and lowers 148the handshake; receiver reads the data and lowers its handshake. 149.Pp 150The packet format has a two-byte header, comprising the fixed values 0x08, 1510x00, immediately followed by the IP header and data. 152.Pp 153The start of a packet is indicated by simply signalling the first byte 154of the header. 155The end of the packet is indicated by inverting 156the data lines (i.e., writing the ones-complement of the previous nibble 157to be transmitted) without changing the state of the handshake. 158.Pp 159Note that the end-of-packet marker assumes that the handshake signal and 160the data-out bits can be written in a single instruction - otherwise 161certain byte values in the packet data would falsely be interpreted 162as end-of-packet. 163This is not a problem for the PC printer port, 164but requires care when implementing this protocol on other equipment. 165.Ss Crynwr/Linux CLPIP mode 166The signal lines are used as follows: 167.Bl -tag -width dataxxxx(Pinxx) 168.It Em Data0 (Pin 2) 169Data out, bit 0. 170.It Em Data1 (Pin 3) 171Data out, bit 1. 172.It Em Data2 (Pin 4) 173Data out, bit 2. 174.It Em Data3 (Pin 5) 175Data out, bit 3. 176.It Em Data4 (Pin 6) 177Handshake out. 178.It Em ERROR* (pin 15) 179Data in, bit 0. 180.It Em SLCT (pin 13) 181Data in, bit 1. 182.It Em PE (pin 12) 183Data in, bit 2. 184.It Em ACK* (pin 10) 185Data in, bit 3. 186.It Em BUSY (pin 11) 187Handshake in. 188.El 189.Pp 190When idle, all data lines are at zero. 191Each byte is signalled in four steps: 192sender writes the 4 least significant bits and raises the handshake line; 193receiver reads the 4 bits and raises its handshake to acknowledge; 194sender places the 4 most significant bits on the data lines and lowers 195the handshake; receiver reads the data and lowers its handshake. 196[Note that this is the opposite nibble order to LPIP mode]. 197.Pp 198Packet format is: 199.Bd -literal 200Length (least significant byte) 201Length (most significant byte) 20212 bytes of supposed MAC addresses (ignored by FreeBSD). 203Fixed byte 0x08 204Fixed byte 0x00 205<IP datagram> 206Checksum byte. 207.Ed 208.Pp 209The length includes the 14 header bytes, but not the length bytes themselves 210nor the checksum byte. 211.Pp 212The checksum is a simple arithmetic sum of all the bytes (again, including 213the header but not checksum or length bytes). 214.Fx 215calculates 216outgoing checksums, but does not validate incoming ones. 217.Pp 218The start of packet has to be signalled specially, since the line chosen 219for handshake-in cannot be used to generate an interrupt. 220The sender writes the value 0x08 to the data lines, and waits for the receiver 221to respond by writing 0x01 to its data lines. 222The sender then starts 223signalling the first byte of the packet (the length byte). 224.Pp 225End of packet is deduced from the packet length and is not signalled 226specially (although the data lines are restored to the zero, idle 227state to avoid spuriously indicating the start of the next packet). 228.Sh SEE ALSO 229.Xr ppbus 4 , 230.Xr ppc 4 , 231.Xr ifconfig 8 232.Sh BUGS 233Busy-waiting loops are used while handshaking bytes, (and worse still when 234waiting for the receiving system to respond to an interrupt for the start 235of a packet). 236Hence a fast system talking to a slow one will consume 237excessive amounts of CPU. 238This is unavoidable in the case of CLPIP mode 239due to the choice of handshake lines; it could theoretically be improved 240in the case of LPIP mode. 241.Pp 242Polling timeouts are controlled by counting loop iterations rather than 243timers, and so are dependent on CPU speed. 244This is somewhat stabilised 245by the need to perform (slow) ISA bus cycles to actually read the port. 246