Re: 2.4.18 serial drops characters with 16654

From: Dan Christian (
Date: Thu Sep 19 2002 - 13:38:48 EST

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.

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