LP(4) Special files LP(4)
lp - line printer devices
lp[0-2] are character devices for the parallel line printers; they have major number 6 and
minor number 0-2. The minor numbers correspond to the printer port base addresses 0x03bc,
0x0378 and 0x0278. Usually they have mode 220 and are owned by root and group lp. You
can use printer ports either with polling or with interrupts. Interrupts are recommended
when high traffic is expected, e.g. for laser printers. For usual dot matrix printers
polling will usually be enough. The default is polling.
The following ioctl(2) calls are supported:
int ioctl(int fd, LPTIME, int arg)
Sets the amount of time that the driver sleeps before rechecking the printer when
the printer's buffer appears to be filled to arg. If you have a fast printer,
decrease this number; if you have a slow printer then increase it. This is in hun-
dredths of a second, the default 2 being 0.02 seconds. It only influences the
int ioctl(int fd, LPCHAR, int arg)
Sets the maximum number of busy-wait iterations which the polling driver does while
waiting for the printer to get ready for receiving a character to arg. If printing
is too slow, increase this number; if the system gets too slow, decrease this num-
ber. The default is 1000. It only influences the polling driver.
int ioctl(int fd, LPABORT, int arg)
If arg is 0, the printer driver will retry on errors, otherwise it will abort. The
default is 0.
int ioctl(int fd, LPABORTOPEN, int arg)
If arg is 0, open(2) will be aborted on error, otherwise error will be ignored.
The default is to ignore it.
int ioctl(int fd, LPCAREFUL, int arg)
If arg is 0, then the out-of-paper, offline and error signals are required to be
false on all writes, otherwise they are ignored. The default is to ignore them.
int ioctl(int fd, LPWAIT, int arg)
Sets the number of busy waiting iterations to wait before strobing the printer to
accept a just-written character, and the number of iterations to wait before turn-
ing the strobe off again, to arg. The specification says this time should be 0.5
microseconds, but experience has shown the delay caused by the code is already
enough. For that reason, the default value is 0. This is used for both the
polling and the interrupt driver.
int ioctl(int fd, LPSETIRQ, int arg)
This ioctl() requires superuser privileges. It takes an int containing the new IRQ
as argument. As a side effect, the printer will be reset. When arg is 0, the
polling driver will be used, which is also default.
int ioctl(int fd, LPGETIRQ, int *arg)
Stores the currently used IRQ in arg.
int ioctl(int fd, LPGETSTATUS, int *arg)
Stores the value of the status port in arg. The bits have the following meaning:
LP_PBUSY inverted busy input, active high
LP_PACK unchanged acknowledge input, active low
LP_POUTPA unchanged out-of-paper input, active high
LP_PSELECD unchanged selected input, active high
LP_PERRORP unchanged error input, active low
Refer to your printer manual for the meaning of the signals. Note that undocu-
mented bits may also be set, depending on your printer.
int ioctl(int fd, LPRESET)
Resets the printer. No argument is used.
The printer driver was originally written by Jim Weigand and Linus Torvalds. It was fur-
ther improved by Michael K. Johnson. The interrupt code was written by Nigel Gamble.
Alan Cox modularised it. LPCAREFUL, LPABORT, LPGETSTATUS were added by Chris Metcalf.
mknod(1), chown(1), chmod(1), tunelp(8), lpcntl(8)