235 lines
8.4 KiB
Groff
235 lines
8.4 KiB
Groff
.\" -*- nroff -*-
|
|
.\"
|
|
.\" Copyright (c) 1996 A.R.Gordon, andrew.gordon@net-tel.co.uk
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $Id: lp.4,v 1.6 1998/10/15 20:36:55 wosch Exp $
|
|
.\"
|
|
.Dd March 4, 1996
|
|
.Os
|
|
.Dt LP 4 i386
|
|
.Sh NAME
|
|
.Nm lp
|
|
.Nd printer port Internet Protocol driver
|
|
.Sh SYNOPSIS
|
|
.Nm ifconfig lp0
|
|
.Ar myaddress hisaddress
|
|
.Op Fl link0
|
|
.Cd "device lpt0 at isa? port? tty irq 7"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
driver allows a PC parallel printer port to be used as a
|
|
point-to-point network interface between two similarly configured systems.
|
|
Data is transferred 4 bits at a time, using the printer status lines for
|
|
input: hence there is no requirement for special bidirectional hardware
|
|
and any standard AT-compatible printer port with working interrupts may be used.
|
|
.Pp
|
|
The
|
|
.Nm
|
|
driver is implemented as an integral part of the
|
|
.Nm lpt
|
|
driver, and will automatically be present in a kernel configured with
|
|
Internet support and at least one
|
|
.Nm lpt
|
|
device. During the boot process, for each
|
|
.Nm lpt
|
|
printer device which is probed and has an interrupt assigned, a corresponding
|
|
.Nm
|
|
network device is created. Available devices are announced with a message
|
|
such as:
|
|
.Dl lp0: TCP/IP capable interface
|
|
.Pp
|
|
Initially, the
|
|
.Nm lpt
|
|
device is active for printing and the network interface is inactive; however,
|
|
once the corresponding
|
|
.Nm
|
|
device has been configured 'up' with
|
|
.Xr ifconfig 8
|
|
printing is disabled until the network interface is configured 'down'.
|
|
.Pp
|
|
The communication protocol is selected by the
|
|
.Cm link0
|
|
flag:
|
|
.Bl -tag -width Fl
|
|
.It Fl link0
|
|
(default) Use FreeBSD mode (LPIP). This is the simpler of the two modes
|
|
and therefore slightly more efficient.
|
|
.It Cm link0
|
|
Use Crynwr/Linux compatible mode (CLPIP). This mode has a simulated ethernet
|
|
packet header, and is easier to interface to other types of equipment.
|
|
.El
|
|
.Pp
|
|
The interface MTU defaults to 1500, but may be set to any value. Both ends
|
|
of the link must be configured with the same MTU.
|
|
.Ss Cable Connections
|
|
The cable connecting the two parallel ports should be wired as follows:
|
|
.Bd -literal
|
|
Pin Pin Description
|
|
2 15 Data0 -> ERROR*
|
|
3 13 Data1 -> SLCT
|
|
4 12 Data2 -> PE
|
|
5 10 Data3 -> ACK*
|
|
6 11 Data4 -> BUSY
|
|
15 2 ERROR* -> Data0
|
|
13 3 SLCT -> Data1
|
|
12 4 PE -> Data2
|
|
10 5 ACK* -> Data3
|
|
11 6 BUSY -> Data4
|
|
18-25 18-25 Ground
|
|
.Ed
|
|
.Pp
|
|
Cables with this wiring are widely available as 'Laplink' cables, and
|
|
are often coloured yellow.
|
|
.Pp
|
|
The connections are symmetric, and provide 5 lines in each direction (four
|
|
data plus one handshake). The two modes use the same wiring, but make a
|
|
different choice of which line to use as handshake.
|
|
.Ss FreeBSD LPIP mode
|
|
The signal lines are used as follows:
|
|
.Bl -tag -width dataxxxx(Pinxx)
|
|
.It Em Data0 (Pin 2)
|
|
Data out, bit 0.
|
|
.It Em Data1 (Pin 3)
|
|
Data out, bit 1.
|
|
.It Em Data2 (Pin 4)
|
|
Data out, bit 2.
|
|
.It Em Data3 (Pin 5)
|
|
Handshake out.
|
|
.It Em Data4 (Pin 6)
|
|
Data out, bit 3.
|
|
.It Em ERROR* (pin 15)
|
|
Data in, bit 0.
|
|
.It Em SLCT (pin 13)
|
|
Data in, bit 1.
|
|
.It Em PE (pin 12)
|
|
Data in, bit 2.
|
|
.It Em BUSY (pin 11)
|
|
Data in, bit 3.
|
|
.It Em ACK* (pin 10)
|
|
Handshake in.
|
|
.El
|
|
.Pp
|
|
When idle, all data lines are at zero. Each byte is signalled in four steps:
|
|
sender writes the 4 most significant bits and raises the handshake line;
|
|
receiver reads the 4 bits and raises its handshake to acknowledge;
|
|
sender places the 4 least significant bits on the data lines and lowers
|
|
the handshake; receiver reads the data and lowers its handshake.
|
|
.Pp
|
|
The packet format has a two-byte header, comprising the fixed values 0x08,
|
|
0x00, immediately followed by the IP header and data.
|
|
.Pp
|
|
The start of a packet is indicated by simply signalling the first byte
|
|
of the header. The end of the packet is indicated by inverting
|
|
the data lines (ie. writing the ones-complement of the previous nibble
|
|
to be transmitted) without changing the state of the handshake.
|
|
.Pp
|
|
Note that the end-of-packet marker assumes that the handshake signal and
|
|
the data-out bits can be written in a single instruction - otherwise
|
|
certain byte values in the packet data would falsely be interpreted
|
|
as end-of-packet. This is not a problem for the PC printer port,
|
|
but requires care when implementing this protocol on other equipment.
|
|
|
|
.Ss Crynwr/Linux CLPIP mode
|
|
The signal lines are used as follows:
|
|
.Bl -tag -width dataxxxx(Pinxx)
|
|
.It Em Data0 (Pin 2)
|
|
Data out, bit 0.
|
|
.It Em Data1 (Pin 3)
|
|
Data out, bit 1.
|
|
.It Em Data2 (Pin 4)
|
|
Data out, bit 2.
|
|
.It Em Data3 (Pin 5)
|
|
Data out, bit 3.
|
|
.It Em Data4 (Pin 6)
|
|
Handshake out.
|
|
.It Em ERROR* (pin 15)
|
|
Data in, bit 0.
|
|
.It Em SLCT (pin 13)
|
|
Data in, bit 1.
|
|
.It Em PE (pin 12)
|
|
Data in, bit 2.
|
|
.It Em ACK* (pin 10)
|
|
Data in, bit 3.
|
|
.It Em BUSY (pin 11)
|
|
Handshake in.
|
|
.El
|
|
.Pp
|
|
When idle, all data lines are at zero. Each byte is signalled in four steps:
|
|
sender writes the 4 least significant bits and raises the handshake line;
|
|
receiver reads the 4 bits and raises its handshake to acknowledge;
|
|
sender places the 4 most significant bits on the data lines and lowers
|
|
the handshake; receiver reads the data and lowers its handshake.
|
|
[Note that this is the opposite nibble order to LPIP mode].
|
|
.Pp
|
|
Packet format is:
|
|
.Bd -literal
|
|
Length (least significant byte)
|
|
Length (most significant byte)
|
|
12 bytes of supposed MAC addresses (ignored by FreeBSD).
|
|
Fixed byte 0x08
|
|
Fixed byte 0x00
|
|
<IP datagram>
|
|
Checksum byte.
|
|
.Ed
|
|
.Pp
|
|
The length includes the 14 header bytes, but not the length bytes themselves
|
|
nor the checksum byte.
|
|
.Pp
|
|
The checksum is a simple arithmetic sum of all the bytes (again, including
|
|
the header but not checksum or length bytes). FreeBSD calculates
|
|
outgoing checksums, but does not validate incoming ones.
|
|
.Pp
|
|
The start of packet has to be signalled specially, since the line chosen
|
|
for handshake-in cannot be used to generate an interrupt. The sender
|
|
writes the value 0x08 to the data lines, and waits for the receiver
|
|
to respond by writing 0x01 to its data lines. The sender then starts
|
|
signalling the first byte of the packet (the length byte).
|
|
.Pp
|
|
End of packet is deduced from the packet length and is not signalled
|
|
specially (although the data lines are restored to the zero, idle
|
|
state to avoid spuriously indicating the start of the next packet).
|
|
.Sh SEE ALSO
|
|
.Xr lpt 4 ,
|
|
.Xr ifconfig 8 .
|
|
.Sh BUGS
|
|
Busy-waiting loops are used while handshaking bytes, (and worse still when
|
|
waiting for the receiving system to respond to an interrupt for the start
|
|
of a packet). Hence a fast system talking to a slow one will consume
|
|
excessive amounts of CPU. This is unavoidable in the case of CLPIP mode
|
|
due to the choice of handshake lines; it could theoretically be improved
|
|
in the case of LPIP mode.
|
|
.Pp
|
|
Polling timeouts are controlled by counting loop iterations rather than
|
|
timers, and so are dependent on CPU speed. This is somewhat stabilised
|
|
by the need to perform (slow) ISA bus cycles to actually read the port.
|