DVFS (i.MX31)

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1 LTIB Configuration

In the Kernel Configuration select

  * Device Drivers -> MXC Support Drivers -> Advanced Power Management Devices -> MXC DPTC Driver
  * Device Drivers -> MXC Support Drivers -> Advanced Power Management Devices -> MXC DVFS Driver
  * Device Drivers -> MXC Support Drivers -> Advanced Power Management Devices -> SDMA

Recompile the kernel.

2 Testing

Run the command

/unit_tests/dvfs_dptc_hi_demo/dvfs_dptc_hi.out

and try working point #12 (reduces core voltage from 1,6V to 1,35V)

If you enable DVFS, and connect and oscilloscope to the pin indicated below, you should be able to see a frequency change depending on the workload. This can easily be checked: Reboot the device and connect the oscilloscope to the pin indicated below. Run the command to enable clock output on the pin as well (please see below). Then start the test application and press "8". The application will say "press any key to continue". In this moment, the application runs in an infinite loop which causes a high cpu load. If you press any key, it will go back into normal mode and you should be able to see a frequency change. You can try this multiple times.

3 Notes

To detect the changes in the frequency, you will need an oscilloscope connected to the pin header X1 Pin 2 (close to the keypad connector). You will further need to set the appropriate register to enable the clock out signal. COSR: 0x53F8 001C (Clock Out Source Register). Write the following value into the register to enable the clock out signal and to set a prescaler of 16 (maximum prescaler): 0x00000306. This can be done by

/unit_tests/memtool/memtool 0x53f8001c=0x306
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