topic Re: cpu clock in i.MX Processors

cpu clock

niklasmolin — Thu, 03 Apr 2014 04:15:38 GMT

Hi.

I'm checking in /proc/cpuinfo between my sabreSD and Sabrelite board.

On the lite it shows BogoMIPS : 1988.28

on the sabreSD, BogoMIPS : 790.52

Does this mean the SabreLite is running with a faster internal clock than the SAbreSD?

If so, how do I change the clock for the SabreSD?

Is thet done in the dts file or somewhere else?

I checked in /sys/devices/system/cpu/cpu0/cpufreq

For SabreSD I can see that cpuinfo_cur_freq is 396000 and on the SabreSD it is 996000.

Regards,

Niklas

Re: cpu clock

niklasmolin — Thu, 03 Apr 2014 15:02:15 GMT

I can see that for SabreSD the cpuinfo_cur_freq changes if the processor is more loaded.

So it seems like it changes the frequency depending on the load.

How quick is this change, can it effect the response time of stuff running in the processor?

Is it possible to change the min_freq that it can scale down to?

Re: cpu clock

AnsonHuang — Fri, 04 Apr 2014 06:23:01 GMT

Hi, Niklas

THe cpufreq change is based on the cpu loading which is got from the cpu idle time;

To change the min_freq, you can echo a freq into /sys/device/system/cpu/cpu0/cpufreq/scaling_min_freq, such as "echo 792000 > /sys/...", then the min freq will set to 792M. You can also cat or echo different setting into these sys fs interface to change the cpufreq setting.

Re: cpu clock

niklasmolin — Fri, 04 Apr 2014 07:12:45 GMT

Hi Yongcai.

Thanks for the reply.

I'll try that tomorrow.

Is it possible to also go up to 1.2 GHz.

If so, where do I set that?

I also saw that the DDR freq is set to 528MHz.

Is that the maximum or is it possible to go higher (we have DDR3 memory on the board)?

I notice that some of our applications (redis and node.js) are going as fast as I expected (especially when there are a lot of reading to the redis database).

Best regards,

Niklas

Re: cpu clock

AnsonHuang — Fri, 04 Apr 2014 07:45:45 GMT

The max cpufreq is defined by the fuse map of speed_grading field, not all chips support 1.2GHz, so you need to read the fuse on your chip to see how high freq it supports.

528MHz is the highest freq we recommend.