Documentation/networking/plip.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 PLIP: The Parallel Line Internet Protocol Device
14 -----------------
16 This document describes the parallel port packet pusher for Net/LGX.
17 This device interface allows a point-to-point connection between two
18 parallel ports to appear as a IP network interface.
23 PLIP is Parallel Line IP, that is, the transportation of IP packages
24 over a parallel port. In the case of a PC, the obvious choice is the
25 printer port.  PLIP is a non-standard, but [can use] uses the standard
26 LapLink null-printer cable [can also work in turbo mode, with a PLIP
40 even be especially important in the case of notebooks, where netcards
44 cables, everything else is software configuration [which in principle
62 -------------------
65 that uses the parallel port subsystem of the kernel in order to properly
66 share parallel ports between PLIP and other services.
71 When a parallel port used for a PLIP driver has an IRQ configured to it, the
76 to a certain parallel port, mainly because it is used by some other device.
77 On these machines, the PLIP driver can be used in IRQ-less mode, where
78 the PLIP driver would constantly poll the parallel port for data waiting,
80 the IRQ mode, because the driver has to check the parallel port many times
82 indicate that there isn't a noticeable performance drop when using IRQ-less
86 When the PLIP driver is used in IRQ mode, the timeout used for triggering a
92 When in IRQ-less mode, the PLIP driver polls the parallel port HZ times
99 10^6/HZ usecs. If both sides of a PLIP connection are used in IRQ-less mode,
102 It appears that in practice, the trigger timeout can be shorter than in the
104 in which case a long timeout would stall the machine when, for whatever
107 A utility that can perform this change in Linux is plipconfig, which is part
108 of the net-tools package (its location can be found in the
114 -----------------------------
117 only one implemented in the early version of the code) uses a standard
122 bi-directional parallel ports, rather than output-only ``printer``
123 ports.  This allows byte-wide transfers and avoids reconstructing
126 Parallel Transfer Mode 0 Cable
139 two DB-25 male connectors symmetrically connected as follows::
142     D0->ERROR	2 - 15		15 - 2
143     D1->SLCT	3 - 13		13 - 3
144     D2->PAPOUT	4 - 12		12 - 4
145     D3->ACK	5 - 10		10 - 5
146     D4->BUSY	6 - 11		11 - 6
150     SLCTIN	17 - 17
152     GROUND	25 - 25
157 connected to the metallic DB-25 shell at one end only.
159 Parallel Transfer Mode 1
163 bi-directional parallel ports, rather than output-only ``printer``
164 ports.  This allows byte-wide transfers, and avoids reconstructing
166 ``printer`` (as opposed to ``parallel``) ports or when the machine
167 isn't configured for PLIP, as it will result in output driver
172     STROBE->BUSY 1 - 11
173     D0->D0	2 - 2
174     D1->D1	3 - 3
175     D2->D2	4 - 4
176     D3->D3	5 - 5
177     D4->D4	6 - 6
178     D5->D5	7 - 7
179     D6->D6	8 - 8
180     D7->D7	9 - 9
181     INIT -> ACK  16 - 10
182     AUTOFD->PAPOUT 14 - 12
183     SLCT->SLCTIN 13 - 17
184     GND->ERROR	18 - 15
186     GROUND	25 - 25
191 be connected to the metallic DB-25 shell at one end only.
196 The PLIP driver is compatible with the "Crynwr" parallel port transfer
197 standard in Mode 0.  That standard specifies the following protocol::
200    count-low octet
201    count-high octet
211 That raises the ACK line, triggering an interrupt in the receiving
217   (OUT is bit 0-4, OUT.j is bit j from OUT. IN likewise)
220      WAIT FOR IN.4 = 1
222      WAIT FOR IN.4 = 0