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From: Dan Christian <dchristian@mail.arc.nasa.gov>
Reply-To: dchristian@mail.arc.nasa.gov
Organization: NASA Ames Research Center
To: Russell King <rmk@arm.linux.org.uk>, Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: 2.4.18 serial drops characters with 16654
Date: Thu, 19 Sep 2002 11:38:48 -0700
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On Thursday 19 September 2002 11:01, Russell King wrote:
> Hmm, looking at the tty stuff, I'd say its a distinct possibility.
>  Even more so since the flip buffer handler is put on tq_timer, which
> is subject to ksoftirqd.
>
>
> However, at the point when we hand data to the tty layer, we should
> have 2048 bytes left in the flip buffer before we really start soft
> overrunning (vs hardware overrunning.)  I notice that we don't make
> any attempt to report such an event to user space, even when user
> space wants to know about overruns.
>
>
> Christian - what baud rate are you running these uarts at?

I've reproduced the drops at very low baud rates.  I didn't take notes, 
but I think that I was getting the same sort of behavior at about 
19.2Kb as 115Kb.

It really doesn't look like a speed thing.  The CPU is >1Ghz and the CPU 
usages is always below 10%.   Since it works with a 16550 (interrupting 
every 16? bytes) and not on a 16654 (interrupting every 64? bytes), it 
doesn't seem like something is too slow.

-Dan
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