User`s guide

2-28
Guide to Printers and Printing
y1 Indicates the maximum number of characters in a data block.
y2 Indicates the number of microseconds to delay between data block
transmissions.
64–Port Controller
The 64–port controller provides hardware support for terminal–attached printers. The
64–port controller has the following virtual printer attribute:
y1 Sets the priority with which printing will be done over terminal activity.
The larger the number, the greater the priority the printer has over the
terminal.
128–Port Controller
The 128–port controller also provides hardware support for terminal–attached printers. The
128–port controller has the following virtual printer attributes:
y1 Sets the maximum characters per second (CPS) rate at which
characters are sent to the print device. The rate should be just below
the average print speed for your printer. Consult your printer’s
documentation for print speed.
y2 Sets the maximum number of print characters the device driver places
in the output queue. Reducing this number increases system overhead.
Increasing this number delays operator keystroke echo times when the
terminal–attached printer is in use.
y3 Sets the device driver estimate of the size of the terminal–attached
printer’s input buffer. After a period of inactivity, the driver bursts the
designated number of characters to the printer. Consult your printer’s
documentation for input buff er size.
Printer Backend Commands
The piobe command is the normal backend program run by the print spooling subsystem
when printing to a locally attached printer device. The piobe comm and is started via the
qdaemon process. It determines the data stream it is going to create by reading a flag or
querying the virtual printer database. The piobe process then passes the print file through a
pipeline of appropriate filters so that it generates the correct data stream. At the end of this
pipeline, the filtered file is passed to the pioout device driver interface program.
The pioout command is invoked in a pipeline by the piobe command. For locally attached
printers, the pioout command sends the print file to the appro priate printer device driver
(for example, /dev/lp1). However, for terminal–attached printers, the print files are sent to
the printer via the tty device driver (for example, /dev/tty0), after being modified by data
gathered from the terminf o and virtual printer databases. The terminfo database is queried
for the mc5 and mc4 terminal control attributes. The virtual printer database is queried for
the asynchronous controller–specific attributes.