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: src/share/man/man4/lp.4,v 1.5.2.3 2000/12/29 10:18:00 ru Exp $ 36.\" $DragonFly: src/share/man/man4/lp.4,v 1.5 2005/08/01 01:49:17 swildner Exp $ 37.\" 38.Dd March 4, 1996 39.Os 40.Dt LP 4 41.Sh NAME 42.Nm lp 43.Nd printer port Internet Protocol driver 44.Sh SYNOPSIS 45.Nm ifconfig 46.Ar lp0 47.Ar myaddress hisaddress 48.Op Fl link0 49.Pp 50.Cd "device ppbus" 51.Cd "device plip" 52.Cd "device ppc0 at isa? port? irq 7" 53.Sh DESCRIPTION 54The 55.Nm 56driver allows a PC parallel printer port to be used as a 57point-to-point network interface between two similarly configured systems. 58Data is transferred 4 bits at a time, using the printer status lines for 59input: hence there is no requirement for special bidirectional hardware 60and any standard AT-compatible printer port with working interrupts may be used. 61.Pp 62During the boot process, for each 63.Nm plip 64device which is probed and has an interrupt assigned, a corresponding 65.Nm network 66device is created. 67.Pp 68Configuring an 69.Nm 70device with 71.Xr ifconfig 8 72causes the corresponding 73.Nm parallel port bus 74to be reserved for PLIP until the network interface is configured 'down'. 75.Pp 76The communication protocol is selected by the 77.Cm link0 78flag: 79.Bl -tag -width Fl 80.It Fl link0 81(default) Use 82.Dx 83mode (LPIP). This is the simpler of the two modes 84and therefore slightly more efficient. 85.It Cm link0 86Use Crynwr/Linux compatible mode (CLPIP). This mode has a simulated ethernet 87packet header, and is easier to interface to other types of equipment. 88.El 89.Pp 90The interface MTU defaults to 1500, but may be set to any value. Both ends 91of the link must be configured with the same MTU. 92.Ss Cable Connections 93The cable connecting the two parallel ports should be wired as follows: 94.Bd -literal 95 Pin Pin Description 96 2 15 Data0 -> ERROR* 97 3 13 Data1 -> SLCT 98 4 12 Data2 -> PE 99 5 10 Data3 -> ACK* 100 6 11 Data4 -> BUSY 101 15 2 ERROR* -> Data0 102 13 3 SLCT -> Data1 103 12 4 PE -> Data2 104 10 5 ACK* -> Data3 105 11 6 BUSY -> Data4 106 18-25 18-25 Ground 107.Ed 108.Pp 109Cables with this wiring are widely available as 'Laplink' cables, and 110are often coloured yellow. 111.Pp 112The connections are symmetric, and provide 5 lines in each direction (four 113data plus one handshake). The two modes use the same wiring, but make a 114different choice of which line to use as handshake. 115.Ss LPIP mode 116The signal lines are used as follows: 117.Bl -tag -width dataxxxx(Pinxx) 118.It Em Data0 (Pin 2) 119Data out, bit 0. 120.It Em Data1 (Pin 3) 121Data out, bit 1. 122.It Em Data2 (Pin 4) 123Data out, bit 2. 124.It Em Data3 (Pin 5) 125Handshake out. 126.It Em Data4 (Pin 6) 127Data out, bit 3. 128.It Em ERROR* (pin 15) 129Data in, bit 0. 130.It Em SLCT (pin 13) 131Data in, bit 1. 132.It Em PE (pin 12) 133Data in, bit 2. 134.It Em BUSY (pin 11) 135Data in, bit 3. 136.It Em ACK* (pin 10) 137Handshake in. 138.El 139.Pp 140When idle, all data lines are at zero. Each byte is signalled in four steps: 141sender writes the 4 most significant bits and raises the handshake line; 142receiver reads the 4 bits and raises its handshake to acknowledge; 143sender places the 4 least significant bits on the data lines and lowers 144the handshake; receiver reads the data and lowers its handshake. 145.Pp 146The packet format has a two-byte header, comprising the fixed values 0x08, 1470x00, immediately followed by the IP header and data. 148.Pp 149The start of a packet is indicated by simply signalling the first byte 150of the header. The end of the packet is indicated by inverting 151the data lines (ie. writing the ones-complement of the previous nibble 152to be transmitted) without changing the state of the handshake. 153.Pp 154Note that the end-of-packet marker assumes that the handshake signal and 155the data-out bits can be written in a single instruction - otherwise 156certain byte values in the packet data would falsely be interpreted 157as end-of-packet. This is not a problem for the PC printer port, 158but requires care when implementing this protocol on other equipment. 159.Ss Crynwr/Linux CLPIP mode 160The signal lines are used as follows: 161.Bl -tag -width dataxxxx(Pinxx) 162.It Em Data0 (Pin 2) 163Data out, bit 0. 164.It Em Data1 (Pin 3) 165Data out, bit 1. 166.It Em Data2 (Pin 4) 167Data out, bit 2. 168.It Em Data3 (Pin 5) 169Data out, bit 3. 170.It Em Data4 (Pin 6) 171Handshake out. 172.It Em ERROR* (pin 15) 173Data in, bit 0. 174.It Em SLCT (pin 13) 175Data in, bit 1. 176.It Em PE (pin 12) 177Data in, bit 2. 178.It Em ACK* (pin 10) 179Data in, bit 3. 180.It Em BUSY (pin 11) 181Handshake in. 182.El 183.Pp 184When idle, all data lines are at zero. Each byte is signalled in four steps: 185sender writes the 4 least significant bits and raises the handshake line; 186receiver reads the 4 bits and raises its handshake to acknowledge; 187sender places the 4 most significant bits on the data lines and lowers 188the handshake; receiver reads the data and lowers its handshake. 189[Note that this is the opposite nibble order to LPIP mode]. 190.Pp 191Packet format is: 192.Bd -literal 193Length (least significant byte) 194Length (most significant byte) 19512 bytes of supposed MAC addresses (ignored by 196.Dx Ns ). 197Fixed byte 0x08 198Fixed byte 0x00 199<IP datagram> 200Checksum byte. 201.Ed 202.Pp 203The length includes the 14 header bytes, but not the length bytes themselves 204nor the checksum byte. 205.Pp 206The checksum is a simple arithmetic sum of all the bytes (again, including 207the header but not checksum or length bytes). 208.Dx 209calculates 210outgoing checksums, but does not validate incoming ones. 211.Pp 212The start of packet has to be signalled specially, since the line chosen 213for handshake-in cannot be used to generate an interrupt. The sender 214writes the value 0x08 to the data lines, and waits for the receiver 215to respond by writing 0x01 to its data lines. The sender then starts 216signalling the first byte of the packet (the length byte). 217.Pp 218End of packet is deduced from the packet length and is not signalled 219specially (although the data lines are restored to the zero, idle 220state to avoid spuriously indicating the start of the next packet). 221.Sh SEE ALSO 222.Xr ppbus 4 , 223.Xr ppc 4 , 224.Xr ifconfig 8 225.Sh BUGS 226Busy-waiting loops are used while handshaking bytes, (and worse still when 227waiting for the receiving system to respond to an interrupt for the start 228of a packet). Hence a fast system talking to a slow one will consume 229excessive amounts of CPU. This is unavoidable in the case of CLPIP mode 230due to the choice of handshake lines; it could theoretically be improved 231in the case of LPIP mode. 232.Pp 233Polling timeouts are controlled by counting loop iterations rather than 234timers, and so are dependent on CPU speed. This is somewhat stabilised 235by the need to perform (slow) ISA bus cycles to actually read the port. 236