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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 hundredths of
a second, the default 2 being 0.02 seconds. It only influences
the polling driver.
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
number. The default is 1000. It only influences the polling
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 turning 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
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 undocumented bits may also be set, depending on your
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 further 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.
chmod(1), chown(1), mknod(1), lpcntl(8), tunelp(8)