Re: [gphoto-kodak] Re: Kodak DC-265 overrunning linux serial driver?

brian@worldcontrol.com
Sat, 20 Nov 1999 01:43:50 -0800

On Fri, Nov 19, 1999 at 06:44:57PM -0500, Theodore Y. Ts'o wrote:
> The problem is that certain other device drivers (and the IDE PIO driver
> is the prime example) keeps interrupts off to long, thus increasing the
> interrupt latency to the point where you start overflowing the FIFO.
> Increasing the buffer which the interrupt routine uses to copy
> characters out of the FIFO isn't going to help, because they're getting
> lost before the interrupt routine even has a chance to run.

I did some testing on my laptop with linux 2.2.13.

So far as I can tell my HD on the laptop is running in DMA mode.
Additionally, the 'hdparm -u 1 /dev/hda' had no effect on the overrun
problem.

It acted pretty much as Jim has described. With the FIFO level mod,
Nearly 100% failure at 115200, 10% failure at 57600.

At 115200 it always fails, so far as I can tell, right away. Long
before any data is actually written to disk.

One of the "other" drivers must be holding of the serial interrupt
for too long.

-- 
Brian Litzinger <brian@litzinger.com>


    Copyright (c) 1999 By Brian Litzinger, All Rights Reserved


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