[Gllug] re: uart overrun problem

Peter Childs blue.dragon at blueyonder.co.uk
Thu Dec 4 08:31:54 UTC 2003

On Thu, 4 Dec 2003, t.clarke wrote:

> A search on the web reveals a setserial package at sourceforge whic has amongst
> other features a 'latency' feature (which is presumably controlled by the rx
> trigger level).   You could try downloading, compiling, and using this.
> Setting a 'low latency' may then cure the problem.
> However, the question still remains as to why this is happening anyway:
> since uart overruns are simply due to the cpu not being able to clear the
> receive buffer on the uart fast enough, the possibilities would seem to be:
> a) running the serial line too fast

4800bps too fast?

> b) cpu too slow

Modern Processor too slow? Serial Lines have been in use for the last 30
years (think again)

> c) cpu overloaded with other non-interruptible load

	As many pages on the internet "Caused by a multi-process"

> d) crap uart with too small a buffer (any decent mobo should be using a 16550
>    or compatible uart)

	You mean 16550A. The 16550 is crap its only got a 1 byte buffer.

> e) problems with the serial driver code ??

	Linux Kernel?

> f) shared interrupt not being handled efficiently ??
> I have a vague feeling that the driver reports on receiver buffer overruns
> - available by interrogating the appropriate /proc filesystem entry.
> A post containing details of your hardware/o-s config might be helpful to
> others to assist.

	I'll have a look at sourceforge.

> Tim
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Peter Childs

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