Documentation/networking/plip.rst

1 .. SPDX-License-Identifier: GPL-2.0
14 -----------------
17 This device interface allows a point-to-point connection between two
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
62 -------------------
72 PLIP driver is signaled whenever data is sent to it via the cable, such that
73 when no data is available, the driver isn't being used.
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,
79 and if such data is available, process it. This mode is less efficient than
81 per second, even when no data at all is sent. Some rough measurements
82 indicate that there isn't a noticeable performance drop when using IRQ-less
83 mode as compared to IRQ mode as far as the data transfer speed is involved.
87 data transfer (the maximal time the PLIP driver would allow the other side
88 before announcing a timeout, when trying to handshake a transfer of some
89 data) is, by default, 500usec. As IRQ delivery is more or less immediate,
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,
108 of the net-tools package (its location can be found in the
114 -----------------------------
116 PLIP uses several different data transfer methods.  The first (and the
118 printer "null" cable to transfer data four bits at a time using
119 data bit outputs connected to status bit inputs.
121 The second data transfer method relies on both machines having
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
129 The cable for the first transfer mode is a standard
130 printer "null" cable which transfers data four bits at a time using
131 data bit outputs of the first port (machine T) connected to the
133 status inputs, and they are used as four data inputs and a clock (data
134 strobe) input, arranged so that the data input bits appear as contiguous
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
162 The second data transfer method relies on both machines having
163 bi-directional parallel ports, rather than output-only ``printer``
164 ports.  This allows byte-wide transfers, and avoids reconstructing
170 The cable for this transfer mode should be constructed as follows::
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.
193 PLIP Mode 0 transfer protocol
196 The PLIP driver is compatible with the "Crynwr" parallel port transfer
200    count-low octet
201    count-high octet
202    ... data octets
210 To start a transfer the transmitting machine outputs a nibble 0x08.
217   (OUT is bit 0-4, OUT.j is bit j from OUT. IN likewise)