From: Paul Fulghum <paulkf@microgate.com>
To: Dick Hollenbeck <dick@softplc.com>
Cc: rmk+serial@arm.linux.org.uk, linux-serial@vger.kernel.org
Subject: Re: PROBLEM: serial port FIONREAD from realtime thread
Date: Tue, 22 Nov 2005 13:12:12 -0600 [thread overview]
Message-ID: <43836D8C.3040307@microgate.com> (raw)
In-Reply-To: <43834F70.4010404@softplc.com>
Dick Hollenbeck wrote:
> Problem Conditions:
>
> 1) linux 2.6.11.7, but possibly other kernels too
> 1) realtime thread
> 2) serial port open()ed *either* with NON_BLOCKING or not
> 3) ioctl( FIONREAD ) always returns zero
> ...
> What causes this? What is the usleep() enabling?
The tty flip buffering uses a workqueue
to push received data to the line discipline.
Your polling loop at raised priority
is probably preventing the workqueue
from being processed by the events
kernel thread.
When you call usleep() your process yields
so receive data can be processed.
Have you tried (just for testing)
lowering your process priority below that
of the events kernel thread?
--
Paul Fulghum
Microgate Systems, Ltd.
next prev parent reply other threads:[~2005-11-22 19:12 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-22 17:03 PROBLEM: serial port FIONREAD from realtime thread Dick Hollenbeck
2005-11-22 19:12 ` Paul Fulghum [this message]
2005-11-22 19:32 ` Dick Hollenbeck
2005-11-22 19:53 ` Paul Fulghum
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