Why is /dev/lp slow?

[Bret Orsburn]

In article <1990Jun1.184946.17448 at cbnewsl.att.com> rubin at cbnewsl.att.com (Mike Rubin) writes:
>In article <110 at westmark.UU.NET> dave at westmark.UU.NET (Dave Levenson) writes:
>>Just upgraded from AT&T SysV/386r3.2 to SysV/386r3.2.2.  Nothing in
>>the hardware has changed....
>>Since upgrading to 3.2.2, the printer has slowed to about 30 cps or so.
>
>Any other board in the system (whether it has a Unix driver installed
>or not) using interrupt 7, will cause this behavior -- it will eat
>some of the interrupts that come from the lp port.
>
>Make sure you have no extraneous boards in your box.
>

A bad cable or connector can do this, too. (At least it could under
Xenix 286, which was the last place I saw this problem.)

If your /ACK signal (Centronics pin 10) is lost, your printer will still
work fine in a polled environment (i.e. DOS) but will slow to a crawl under
Unix (an interrupt-driven environment).



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Bret Orsburn