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From: terry@cs.weber.edu (A Wizard of Earth C)
Subject: Re: [386bsd] 16550 and rtscts patch
Message-ID: <1992Dec14.171834.7500@fcom.cc.utah.edu>
Sender: news@fcom.cc.utah.edu
Organization: Weber State University (Ogden, UT)
References: <Bz25Io.L40@ucunix.san.uc.edu>
Date: Mon, 14 Dec 92 17:18:34 GMT
Lines: 46
In article <Bz25Io.L40@ucunix.san.uc.edu> pmartin@eniac.san.uc.edu (Paul Martin) writes:
>
>I applied the rtscts flow control patch to the com driver that was
>posted here sometime back. Now I cannot send anything to the modem. The
>modem does not receive the characters, and the command:
>echo ats0=1 > /dev/com2
>seems to hang until I shut off the modem. This worked before the patch.
>I am using 16550's. By the way, the mouse on com1 still works fine.
>
>Any Ideas?
I haven't had a chance to look at the patch yet (I did save it off);
I suspect that the problem is that the inverse level is being looked at
(ie: only with the RTS deasserted can you send). The other possibility
is that the CTS assert/RTS require order is munged, and your modem needs
your serial prot to assert before it can assert, and your serial port
needs the same (ie: starvation deadlock).
In general, it can be said that *nobody* does CTS/RTS as "expected", and
unless you have a Bell 103 dataset, you can't expect it to work quite
right without a lot of tweaking.
The other possibility is that *many* modems will not assert RTS until
they have carrier; this is fine for dial-in to a UNIX box, but dial out
expects to be able to dialog with the modem without DCD *or* RTS
present. If you are using a "calling unit" version of the device, this
problem should be taken care of for you on dial out (although I can't
vouch for whether or not the patch only applies to "calling unit"
devices AFTER DCD has been asserted.
I assume since you can "shut off" your modem that it's external. If you
have a breakout box, you may want to watch the signal levels to/from
the modem to confirm your problem.
Terry Lambert
terry@icarus.weber.edu
terry_lambert@novell.com
---
Any opinions in this posting are my own and not those of my present
or previous employers.
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