linux-kernel - Dropped characters in serial connection without flow control

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Message-ID: <20091028175937.27472.qmail@stuge.se>
Date:	Wed, 28 Oct 2009 18:59:37 +0100
From:	Peter Stuge <peter@...ge.se>
To:	linux-kernel@...r.kernel.org
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Greg KH <greg@...ah.com>
Subject: Dropped characters in serial connection without flow control

Peter Stuge wrote:
> I'm writing a line discipline for a serial port multiplexing
> hardware

There is no(!) support for flow control in the hardware.

Is there anything I can do to reduce serial port interrupt latency or
otherwise try to mitigate this in my ldisc or in Linux in general? I
realize that it will never be quite reliable without any flow
control.

Baud rate is currently 115200 but could become 57600.

Is there something in particular that I can do wrong or right in
the ldisc?

Might it be a good idea to add a circ_buf in the receiver path and
move out any and all attempts at parsing incoming data? Currently
it has a simple message buffer and a state machine in there.

Characters are dropped both going out and coming in. Nothing to do
about the out direction, but maybe input can be made reliable?

I don't expect it, but maybe you know a trick?

//Peter
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