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Date: Wed, 22 Jan 1997 05:39:43 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199701211839.FAA14689@godzilla.zeta.org.au>
To: freebsd-hackers@freebsd.org, luoqi@watermarkgroup.com
Subject: Re: My sportster internal modem doesn't work after switched to 2.2-BETA
Sender: owner-hackers@freebsd.org
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>After some poking around, I found that the if I sent multiple bytes
>to the modem, some would get lost. So I went to sio.c and changed
>com->tx_fifo_size to 1 from 16, and everything works fine now.
>But I am still wondering if this is a problem with the modem, or with
>the software. It seems that NT is doing the same, sending no more than
>one
>byte at a time. This is not a satisfactory solution, the output FIFO
>is underutilized and CPU is servicing 16 times more interrupts.

Which version did it work in?  The sio driver streams output better
than it used to.  There used to be a small amount of dead time every
256(?)  characters.  Perhaps the internal modem can't quite keep up
and its flow control doesn't work or you're not using flow control.
Reducing com->tx_fifo_size gives flow control a better chance of working.

Try other values < 16 for com->tx_fifo_size.

Bruce