and connecting an oscilloscope:

We clearly see that the voltages change (I did start in idle and type

"apt-get update" and ENTER).

Voltages are quite exactly what I have defined in the OPP DT, i.e. 840/880mV going

up to 1100mV.

What you also can see is such voltage steps occur not faster than

every 300ms.

There is some noise on the supply line but that can be an artifact

of the setup and the oscilloscope precision (8bit).

What I have planned to do is a similar test with 1.25GHz and high-load

loops.

Interestingly we can even underclock the OMAP5 down to 250 MHz and it appears

to run stable as well.

root@letux:~# cpufreq-info 
cpufrequtils 008: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq@vger.kernel.org, please.
analyzing CPU 0:
  driver: cpufreq-dt
  CPUs which run at the same hardware frequency: 0 1
  CPUs which need to have their frequency coordinated by software: 0 1
  maximum transition latency: 350 us.
  hardware limits: 250 MHz - 1000 MHz
  available frequency steps: 250 MHz, 500 MHz, 750 MHz, 1000 MHz
  available cpufreq governors: conservative, userspace, powersave, ondemand, performance
  current policy: frequency should be within 250 MHz and 1000 MHz.
                  The governor "ondemand" may decide which speed to use
                  within this range.
  current CPU frequency is 250 MHz (asserted by call to hardware).
  cpufreq stats: 250 MHz:81.74%, 500 MHz:12.91%, 750 MHz:2.24%, 1000 MHz:3.11%  (516)
analyzing CPU 1:
  driver: cpufreq-dt
  CPUs which run at the same hardware frequency: 0 1
  CPUs which need to have their frequency coordinated by software: 0 1
  maximum transition latency: 350 us.
  hardware limits: 250 MHz - 1000 MHz
  available frequency steps: 250 MHz, 500 MHz, 750 MHz, 1000 MHz
  available cpufreq governors: conservative, userspace, powersave, ondemand, performance
  current policy: frequency should be within 250 MHz and 1000 MHz.
                  The governor "ondemand" may decide which speed to use
                  within this range.
  current CPU frequency is 250 MHz (asserted by call to hardware).
  cpufreq stats: 250 MHz:81.74%, 500 MHz:12.91%, 750 MHz:2.24%, 1000 MHz:3.11%  (516)
root@letux:~# 

This was done with these OPP:

&cpu0 {
operating-points = <
/* kHz    uV */
250000 800000
500000 850000
750000 950000
1000000 1050000
// 1250000 1150000
// 1500000 1250000
// 1700000 1250000
>;
};

As you can see I plan to run a slightly lowered 1.25GHz OPP voltage to

be linear between 500 MHz and 1500 MHz.

BR,

Nikolaus