linux-kernel - Re: serial flow control appears broken

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Message-ID: <46AA32C5.9080705@howardsilvan.com>
Date:	Fri, 27 Jul 2007 11:00:37 -0700
From:	Lee Howard <faxguy@...ardsilvan.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Uwe Kleine-König 
	<ukleinek@...ormatik.uni-freiburg.de>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: serial flow control appears broken

Alan Cox wrote:

>As the flow control is driven by software on most 16x50 chips (there are
>a couple of exceptions) if we fail to empty the fifo fast enough then any
>flow control will be asserted too late to save the day.
>
>If you stop the application and do the following
>
>	cat /dev/ttywhatever
>	^Z
>	[stopped]
>
>(so you are asking the OS to buffer data but not ever reading it)
>
>and then fire data at it does the flow control eventually occur ?
>

Yes it does appear to.  I told the application to simply sleep(300) at 
the appropriate moment, and I watched the application and when it began 
the sleep I ran:

  cat /dev/ttyS1
  (lots of "garbage" began spewing forth)
  ^Z
  (about 2 or 3 seconds and the RTS light goes dark)

Thanks,

Lee.

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