Date: Tue, 25 May 1999 10:29:50 -0400 From: Graeme Tait <graeme@echidna.com> To: Terry Glanfield <terry@program-products.co.uk> Cc: freebsd-questions@freebsd.org Subject: Re: console terminal server and power loss Message-ID: <374AB3DE.C07ABB41@echidna.com> References: <9905251324.AA03380@program-products.co.uk>
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Terry Glanfield wrote:
>
> Hi,
>
> Please forgive me if this is not strictly on topic.
>
> I have an old 386 that I'm trying to configure as a terminal server
> for several Sun's serial consoles. Everything works fine except that
> when the power is dropped on the server, a BREAK is sent to all the
> serial ports resulting in the Suns dropping down to the boot prompt.
> I'm trying to do this on the cheap so switched power supplies is out.
> I'm using 3.2-STABLE if that makes any difference. Any other
> suggestions gratefully received.
For RS-232C communication, "break" is signalled by a prolonged absence of high
("mark") on the transmitted data line - so you can detect a literal line break,
or shorted line, etc., that would result in loss of ability to transmit. The
Suns may also monitor and react to other control signals that are part of the
serial interface.
With a bit of effort and some hardware expertise, you could probably cobble
something together that would prevent loss of power in the 386 from creating a
line break condition. E.g., if DTR (data terminal ready) from the 386 is not
true, pull TD (transmitted data), and (any other lines used by the Suns) high.
You'd have to be careful that this worked even in transient, ill-defined states
that might arise during power-down of the 386.
But it would seem much better and easier if the Suns could be configured to
ignore line breaks.
--
Graeme Tait - Echidna
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