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Nexus7 Power Measurement

Steve Conklin did an initial investigation on the power consumption on the Nexus7 by watching the I2C bus and doing some disassembly of the unit:

• Initial Nexus7 Power Investigation (ODP)

• git repo for tools mentioned in the above presentation: git@github.com:sconklin/nexus-tools.git (https://github.com/sconklin/nexus-tools)

Identifying Issues

The same tools used to identify power issues for other architectures (like powertop) work just fine:

• Identifying Power Management Issues

• Measuring CPU usage is a good way to detect when your application is drawing too much power, kcachegrind and callgrind (part of Valgrind) are excellent tools.

Statistics

Colin King maintains several tools to gather statistics on power consumption:

• Powerstat: measures the power consumption of a laptop using the ACPI battery information. The output is like vmstat but also shows power consumption statistics. At the end of a run, powerstat will calculate the average, standard deviation and min/max of the gathered data. $ sudo apt-get install powerstat $ sudo powerstat

• Eventstat: calculates the rate of events per second and can dump the data in a .csv $ git clone git://kernel.ubuntu.com/cking/eventstat.git $ cd eventstat; make $ sudo ./eventstat

Hardware Tools

The ARM Energy Probe is a hardware tool that is fairly cheap and can be used to measure power consumption. It uses a GPL software stack and offers command-line and HTML5+websockets interface. Here is an intro video on using the ARM Energy Probe.