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I have been following the list for the last month or so and notice a lot of Sun - ZyXEL users out there. I tried to get FlexFAX going with hardware flow control on the sun and was told by the list that this is not possible.
Does anyone know why? I have been talking to Sun here who said they used truefax software and "did not do anything special with flow control."
I'd like to recap the current status of the SUN RTS/CTS flow control problems, and see if anyone has anything further to add. Perhaps these problems should go noted in a README file in the port/sun directory. I'm running SunOS 4.1.1 with a U1496E+ with 6.00 ROMS and FlexFAX beta 97. Here is the problem as I see it:
The Sun driver for the Sparcstation on-board zs serial port behaves somewhat differently than one may expect. If hardware flow control is requested by the host and carrier detect is not asserted by the modem then data from the modem to the Sun is discarded. Note that data from the host to the modem works fine under these conditions. Once carrier detect is asserted, RTS/CTS works as expected. The problem is that when flexfax awaits responses from its 'AT' commands, the replies are thrown away by the OS since Carrier Detect is not present.
One would think that the recent changes to FlexFAX in regards to setting the CLOCAL bit would fix this problem. However, it appears that the CLOCAL bit is having no effect.
As mentioned by Steven Grimm, and further verified by looking at the data sheets, the problem arises from the Zilog Z8530 chip used for serial communications. On that chip there is a single control bit which turns on automatic RTS/CTS handling. This same bit turns the CD input into a receiver enable. Thus if the hardware is set for RTS/CTS flow control, then input is discarded whenever CD is inactive. This explains why the OS can't do what we'd like when CLOCAL is set.
One fix for this is to set the modem to always assert CD using AT&C0. However, this will cause problems in disconnecting after a call is finished. Another fix is to use XON/XOFF flow control, but effective RTS/CTS would be better, especially for data connections.
I believe the only way we are going to get around this problem is if FlexFAX would allow independent flow-control selection for setup, data transfer, and FAX transfer. This would also help out handling for modems like the ZyXEL which always do Xon/Xoff flow control when sending faxes.
An infamous and long-standing hardware flow control problem with Sun's
built-in serial ports, which Sun customers have often been led to
believe was insoluable, has at last been solved.
Sun has released a new jumbo tty patch 100513-04 for SunOS 4.1.2 and
4.1.3 that incorporates changes that I have developed for the ZS 8530
serial communications driver (which most notably affects the built-in
serial ports) to support bidirectional hardware flow control.
My changes eliminate a problem in which the receiver is disabled if
CRTSCTS mode is enabled but CD (carrier detect) is not present, and
add support to lower RTS (request to send) when the input buffers are
getting full and reassert it when the buffers drain.
If you are not running SunOS 4.1.2 or 4.1.3 but you have a software
support contract with Sun and are interested in seeing this enhancement
supported in the release you are running, I suggest you contact your
Sun software support representative.
I would like to take this opportunity to thank Dr. R. P. C. Rodgers of
the National Library of Medicine Lister Hill Center, Peter Glassenbury
of the University of Canterbury, Christchurch, New Zealand, and
Arborvitae Software, all of whom provided invaluable assistance.
From: katzung@katsun.chi.il.us (Brian Katzung)
To: flexfax@sgi.sgi.com
Subject: Bidirectional hardware flow control for Sun zs users!
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