Xenix386 & Telebit-Plus

[Michael Henning]

In article <5455 at turnkey.TCC.COM>, sandy at turnkey.TCC.COM (Sanford 'Sandy' Zelkovitz) writes:
> I finally found out why the Telebit wasn't running under RTS/CTS Flow
> Control! It turns out that it wasn't the modem. It is either the driver
> for the standard comm ports or my cable going to the modem. When I hooked
> the modem up to the Smart Multi-port card, all works as advertised!
> 

As it turns out, the problem is in uucico. Xenix introduced the rtsflow and
ctsflow stty flags a while ago. The idea is that RTS/CTS handshaking is done
only when rtsflow/ctsflow are set on the terminal. Unfortunately, uucico
puts the modem port into raw mode, which means that -rtsflow, -ctsflow,
-ixon and -ixoff are all set. In other words, as soon as uucico starts up,
there is no handshaking whatsoever left with the modem, which of course
causes big problems with a Trailblazer.

The reason that it works with your smart card is probably that the vendor
has chosen to ignore the rtsflow/ctsflow flags, which means that hardware
handshaking is in effect regardless of the stty settings.

For our own smart card, we chose to support the new Xenix flags, but we
provide an override which allows you to force hardware handshaking on a port
regardless.

Either solution works, although I believe the second one to be better since
it provides full Xenix compatibility.

Another way to get around the problem is to disable hardware handshaking
completely at the modem end. This means that the Trailblazer keeps CTS
permanently asserted and ignores RTS transitions on the port. If you are
running in PEP mode, with the uucp g-protocol enabled, then the uucico
emulation done by the modem will effectively provide flow control through
acknowledgement packets. We found that this method works well and can give
throughputs of up to 50kBytes/minute on a good phone line.


					Michi.


-- 
               | The opinions expressed are my own, not those of my employer. |
               |                                                              |
               | Michael (Michi) Henning                                      |
               | - We have three Michaels here, that's why they call me Michi |