Subject: Problem with clock_gettime()
To: None <firstname.lastname@example.org>
From: Ian McIntosh <email@example.com>
Date: 11/24/2003 10:45:59
I have encountered an interesting problem in NetBSD 1.5.1
with clock_gettime. I am currently running tests with a
custom designed PCI frame grabber. My current test is to
stress the PCI bus a little to try and determine the
maximum DMA transfer rate I could possibly get.
When doing this I have noticed some strange behaviour
with clock_gettime(). I can call clock_gettime() and
store the result in a temporary variable and then
when I call it again the time returned is before
the time in the temporary variable (indicating that
time has gone backwards????). The time difference
is only ever a few milli-seconds. I have even tested
this when the bus is not that stressed but is still
fairly busy. The problem only appears when the bus is
busy for extended periods of time. When the bus is
not busy then everything seems fine.
Here is the core of the test program I run.
assert; // asserts and stops program.....
// ..time has gone backwards
I have operators to correctly compare timespec values
and make them = and so on. Anyone have any ideas that
can explain this? If so I would very much like to know.