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From: gusw@zedat.fu-berlin.de (Gunther Schadow)
Newsgroups: comp.unix.programmer,comp.unix.bsd.freebsd.misc
Subject: How prevent character loss on SIO?
Date: 14 Aug 1996 02:51:49 GMT
Organization: Freie Universitaet Berlin
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Message-ID: <4urf05$fsg@fu-berlin.de>
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Xref: euryale.cc.adfa.oz.au comp.unix.programmer:41335 comp.unix.bsd.freebsd.misc:25471
I have go a big problem with serial line IO. I am loosing characters
when there is high load on the machine, and I have no clue what to do.
The problem is that the lines are either 3-wire (via glas fibers) or
the other side (to which I have no influence) just doesn't use hard
flow control. Now I thought that by enabling the IXON and IXOFF bits I
could enable soft flow control, but I fear that the TTY device just
doesn't send a STOP character when it's buffer is full, or, it comes
too late to handle the interrupt from the SIO to read the data before
this is overwritten?
I need some help from someone who has some more TTY experience (seems
like networking experience is more en voge nowadays, and I would so
much like to dump the RS232 shit into the trashbin #@!*) To be more
specific:
1. is the IXOFF sending of a STOP character handled automatically
by the SIO device driver?
2. if yes, then would hard flow control improve the situation? I mean
-- suppose I could use hard frow control, would the character loss on
times of high system load be avoided? (i guess no)
3. would FIFO chips *fix* this problem? Right now we use 81450 UARTs
but the *550 would require to change the motherboard.
4. BTW: is a faster board/CPU and memory upgrade necessary? I can't
believe that serving just two serial lines requires a RISC
processor?
5. Currently the SIOs are served by two quite sizable C++ programs
that are performing numerous network communications on behalf of the
serial communication, is a restructuring of the system required to
make the SIO service faster?
I guess that the answer on each of these question is ``yes, sure, fast
hardware -- less problems'', but I need to know what is really
required and what is just a ``nice to have'', and what I could
improve on the software side.
any help is *so much* appreciated -- a very high level data
interchange project is about to loose it's practicability, if I cannot
get the SIOs to run reliably :-(
regards,
Gunther Schadow
--
Gunther Schadow------------------Windsteiner Weg 54a, Berlin 14165, FR. Germany
Dept. of Anaesthesia, Benjamin Franklin University Hospital, Berlin.
gusw@fub46.zedat.fu-berlin.de | http://userpage.fu-berlin/~gusw
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