1kHz timer behavior on Cyclone V

[Janet Schneider]

Hi - thanks for the responses!


It is a very simple application that is only processing a 1 kHz timer for the purposes of this test.  There is no other CPU load on the system.  The only thing I do right now when the timer fires is calculate the time difference since the last timer fired.  Once a second, I output the average, min and max for that second.


I do have a delay it the main task, since it is just sitting there idle.  Would that account for such an increase in the time between the timer firing?


I will try the POSIX API next.


Thank you,

Janet

________________________________
From: Joel Sherrill <joel at rtems.org>
Sent: Wednesday, December 7, 2016 1:15:23 PM
To: Janet Schneider
Cc: users at rtems.org
Subject: Re: 1kHz timer behavior on Cyclone V



On Wed, Dec 7, 2016 at 11:44 AM, Janet Schneider <janetsc at fb.com<mailto:janetsc at fb.com>> wrote:

Hello,


I am running a 1kHz timer test on the Altera Cyclone V dev board.  I am trying to measure the average time period between the timer firing, and any variance on that latency.


I'm seeing an average of 1003 microseconds between the timer firing.  About once a second, I see the maximum time between the timer firing go up to 2500-3000 microseconds.


There are two sets of timers. One is per clock tick and one is per second.

My guesses are:

Do you have a sleep/delay statement in your thread?
There may be some work updating the time that occurs once per second. The implementation of this area has changed so I don't remember offhand if this is still the case.



I'm using rtems_clock_get_uptime_nanoseconds() to measure the time that the timer fires.  I have CONFIGURE_MICROSECONDS_PER_TICK set to 500.


What happens when the HW interrupt timer fires?

--joel

Has anyone else seen this (or something similar)?  Any ideas what might be happening here?


Thanks,

Janet

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