[lug] 16550 Serial port buffering?

Scott A. Herod herod at interact-tv.com
Thu May 24 17:50:02 MDT 2001

After 3 days of trying to get it to work....

  "man setserial"  search for low_latency.

Apparently it was the serial port driver, not context switching
in the kernel.


"Scott A. Herod" wrote:
> Hello,
>   We're having a hard time getting rapid response from a clock attached
> to the 16550 serial port on my machine.  This is RH 7.1 with the
> 2.4.2 kernal.  We believe that we're seeing a big delay ( on the order
> of 10 msecs ) between the time the clock sends a byte and the
> time that select in a user-land process returns with that byte.
>   A couple of questions:
>   Is this an indication of context switching and if so is it possible
> to speed it up?
>   Is there a way to trigger another line on the serial port when the
> read occurs so that I can watch a scope to verify that I am getting
> this delay?
>   Any other thoughts would be greatly appreciated.
> Thanks,
> Scott
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