PLIP(4) BSD Programmer's Manual (i386) PLIP(4)
plip - networking via the standard PC parallel port
option PLIP # Ethernet over parallel port lpt0 at isa? port 0x378 irq 7 # standard PC parallel ports lpt1 at isa? port 0x278 irq 5 lpt2 at isa? port 0x3bc # Hercules cards don't have an IRQ
The plip network interface shows up as plip0 when using lpt0, as plip1 when using lpt1, and as plip2 when using lpt2. A parallel port can not drive a plip interface when configured without an IRQ. The port can be used to drive other devices when the corresponding plip interface is configured down. The plip interface simulates Ethernet on a parallel cable with special wiring (see below), known as a "parallel LapLink cable" (formerly) widely available from PC shops. Its acronym is derived from SLIP and means "Parallel IP Protocol", which, in fact, is wrong: it can handle any protocol available on Ethernet, not just IP. Although a plip connection always is point-to-point, the interface is configured like every standard Ethernet interface and uses ARP to find its neighbour. This is inefficient but provides interoperability with other operating systems. Set the link2 flag on the interface if it is not working. Please report back if it helps for you.
plip uses the (Linux-compatible) Crynwr protocol (CLPIP, Crynwr line- printer IP) defined by Russel Nelson <email@example.com>. This makes it interoperable with the (formerly GPL-licenced, now Public Domain) packet driver "PLIP.COM" available from http://www.crynwr.com/drivers/plip.zip for MS-DOS, as well as Linux 1.3 (make sure to configure the interface to use ARP when connecting to a Linux system) and up.
The following describes the connection of two male 25 pin Sub-D connec- tors which fit into standard PC parallel ports (not to be confused with Centronics connectors, which fit into dot-matrix printers of that time). In Linux, this is known as a "Parallel Transfer Mode 0 Cable". INIT(16) INIT(16) SLCTIN(17) SLCTIN(17) GROUND(25) GROUND(25) D0(2) ERROR(15) D1(3) SLCT(13) D2(4) PAPOUT(12) D3(5) ACK(10) D4(6) BUSY(11) Additional grounds are 18, 19, 20, 21, 22, 23 and 24. Do not connect STROBE(1), D5(7), D6(8), D7(9), and FEED/AUTOFD(14). Linux suggests to not connect INIT(16) either. FreeBSD recently suggests to not connect both INIT(16) and SLCTIN(17).
ifconfig(8), pppd(8), slip(8)
Matthias Pfaller wrote the original NetBSD pc532 version. Martin Husemann ported it to the NetBSD i386 . Thorsten Glaser first ported the port of the NetBSD i386 version for OpenBSD by Pablo Ruiz Garcia to MirOS, then re-did the port using a newer NetBSD source version for MirOS #7.
The plip driver has not yet been successfully tested on MirOS. The driver uses a hard-coded network soft interrupt, which is the only thing that makes it i386 architecture dependent. As soon as generic soft interrupt allocation is available, this should be changed, which would make the driver machine independent (but still dependent on the ISA parallel port architecture). The protocol is too much overhead, a bidirectional input/output routine switchable to a well-designed network line discipline with on-line compression would be far superior. FreeBSD does this, but it makes it im- possible to communicate with MS-DOS and Linux boxen. There are some parallel ports which can use all 8 data bits for input and output, you can make up a parallel handshake protocol and a cable with different wiring to get an 8 bit clean (instead of the current 4 bit) data path out of this. In Linux, this is known as a "Parallel Transfer Mode 1 Cable". This is currently not supported. There is apparently work on the way (the parbus) which will integrate this and other parallel-port devices (zip drives e.a.) more smoothly. The plip driver is said to currently be unable to drive a protocol other than IPv4.
Go buy a pocket Ethernet adaptor or a PCMCIA Ethernet adapter and write a driver for it. It has much better throughput, lower load, and a less cou- pled system between client and server. MirOS BSD #10-current September 2, 2016 1
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