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From: paradis@encore.UUCP (Jim Paradis)
Newsgroups: comp.os.minix
Subject: Problems with serial TTY driver
Message-ID: <2314@encore.UUCP>
Date: Tue, 8-Dec-87 11:57:28 EST
Article-I.D.: encore.2314
Posted: Tue Dec  8 11:57:28 1987
Date-Received: Sun, 13-Dec-87 11:45:19 EST
Organization: The Whizzo Chocolate Company
Lines: 31

After many weeks of not quite being able to get around to it,
I finally added serial line support to my rewritten MINIX TTY
driver.  It works, but there's one serious problem: If I test
it out by looping back transmit and receive on the serial line
and running a quick&dirty terminal program, if I type at it
too fast the system will hang.  Now, I remember someone else in
this newsgroup sometime back who added serial capabilities to
the stock TTY driver and ended up with the same problem.  Is there
some limit to how fast MINIX will take interrupts?  If one takes
them too fast, will messages get lost?

A little background info:  I'm running a 12 MHz AT-clone with
an AST-sixpack-clone board for serial I/O.  The TTY driver takes
interrupts for both "data ready" and "transmit register empty".
I've tried a number of techniques for minimizing the number of
interrupts processed, including doing all writes synchronously
(thereby only having to process data-ready interrupts), waiting 
around for a period of time after a character comes in to see if
there's another immediately following, all to no avail.  I'm
running the serial line at 1200 baud (the default MINIX ioctl
structure has no way of specifying baud rates, so it's hard-coded
for now.  Eventually I'll fix ioctl).

Any ideas out there?  Am I missing something obvious?

   +----------------+  Jim Paradis                  linus--+
+--+-------------+  |  Encore Computer Corp.       necntc--|
|  | E N C O R E |  |  257 Cedar Hill St.           ihnp4--+-encore!paradis
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But if we took the bones out it wouldn't be crunchy, now would it?