On 10-03-16 18:48, Moritz Fischer wrote:
Hi Mike,
On Thu, Mar 10, 2016 at 3:01 AM, Mike Looijmans <mike.looijm...@topic.nl> wrote:
On 10-03-16 11:17, Nathan Rossi wrote:
On Thu, Mar 10, 2016 at 7:29 PM, Mike Looijmans <mike.looijm...@topic.nl>
wrote:
After migrating to the current 4.4 kernel, I noticed that the internal
timer
no longer works correctly.
When the CPU frequency scaling sets the CPU speed to 333MHz, the "wall
clock" time also slows down to half the normal rate (e.g. a "sleep 1"
will
actually take 2 seconds).
This wasn't the case on the 4.0 kernels.
Is this only on linux-xlnx kernels? or linux-yocto and or mainline kernels
too?
It's quite easy to test on ANY kernel, just set the CPU to 333MHz,
typically:
echo 333333 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
and then check how long "sleep 1" really takes.
(Most boards default to "userspace" governor, setting the governor to
"ondemand" will also reduce the speed)
This is a known issue with Zynq. Stuff also horribly breaks if you run
speedgrade 3 devices with cpufreq,
as the prescaler hack goes horribly wrong for these. The issue is that
the cadence ttc's clock depends on
the cpu clock ... which changes ...
The 'prescaler hack' is apparently still present in the 4.4 kernel code. The
problem is that it no longer works, not even on the speedgrade 1 devices (with
only 333 and 666 MHz setpoints).
The frequency scaling saves about 40mA CPU current so I would really like to
keep it, even in its limited form.
I just turn off cpufreq on my Zynq targets since it breaks the timers
for non speedgrade 1 devices and
use the arm global timer instead.
I'm confused by that last remark. What do you mean by "use the arm global
timer instead"?
Kind regards,
Mike Looijmans
System Expert
TOPIC Embedded Products
Eindhovenseweg 32-C, NL-5683 KH Best
Postbus 440, NL-5680 AK Best
Telefoon: +31 (0) 499 33 69 79
E-mail: mike.looijm...@topicproducts.com
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