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Date: Tue, 02 Jul 96 10:32:07 PST
From: "Brett Glass" <Brett_Glass@ccgate.infoworld.com>
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To: Bruce Evans <bde@zeta.org.au>, bde@zeta.org.au, hdalog@zipnet.net,
        msmith@atrad.adelaide.edu.au
Cc: Kevin_Swanson@BLaCKSMITH.com, chuckr@glue.umd.edu,
        freebsd-hardware@FreeBSD.org, jparnas@jparnas.cybercom.net
Subject: Re: muliport boards - building a PPP dialup server
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> If the UART's fifo is larger than about 128, then the pseudo-dma buffers
> won't be able to take all the input.  Flow control may fix the problem in
> practice (just like it does for a modem with a bug buffer connected to a
> UART with a small fifo).

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.

--Brett