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Date: Wed, 3 Jul 1996 03:54:03 +1000
From: Bruce Evans <bde@zeta.org.au>
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To: Brett_Glass@ccgate.infoworld.com, bde@zeta.org.au, hdalog@zipnet.net,
        msmith@atrad.adelaide.edu.au
Subject: Re: muliport boards - building a PPP dialup server
Cc: Kevin_Swanson@BLaCKSMITH.com, chuckr@glue.umd.edu,
        freebsd-hardware@FreeBSD.org, jparnas@jparnas.cybercom.net
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>This brings up a problem I'd forgotten about: slow modem response to flow
>control signals. Often, the modem's internal firmware gives flow control
>such a low priority that several hundred characters can escape before a
>dropped "Clear to Send" signal is recognized. A UART with a big FIFO can
>help, especially if the UART does not have automatic flow control.

The modem needs to recognize flow control within 100-200 characters for
the default FreeBSD buffer sizes.

Flow control can't be depended on to prevent fifo overflows in the UART
because the sender can't be depended on to stop before sending more
characters than fit in the fifo.

Bruce