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From: Javier Martin Rueda <jmrueda@diatel.upm.es>
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Subject: frequent errors "tty-level buffer overflow"
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I have a 486DX2-66 that is serving two printers: a PostScript connected
to the paralell port, and an HP LaserJet III connected to the serial
port at 9600 bps. The serial port has a 16450 UART.

Quite often I'm getting messages such as:

...
sio0: 961 more tty-level buffer overflows (total 103188)
sio0: 960 more tty-level buffer overflows (total 104148)
sio0: 960 more tty-level buffer overflows (total 105108)
...

And print jobs are output incorrectly, because chars seem to be lost. The
man page for sio(4) says that is a problem in the application.

At 19200 bps, things are worse, and almost any print job has errors.

My printcap entry for the printer is:

lj|hp|HPLaserJetIII:\
        :br#9600:lp=/dev/cuaa0:mx#0:sh:\
        :lf=/var/spool/lpd/ljlog:sd=/var/spool/output/lpd/lj:\
        :af=/var/spool/lpd/ljacct:if=/usr/local/bin/contapcl:

If anybody has encountered and solved this problem, can you please tell
me how? Thanks in advance.

Note: although that is not the only activity of the machine, it is idle or
with a low load of work most of the time.