Power Management

Update:
After much screwing around building custom kernels.  I have managed to get the board to standby and wakeup from the uart0.

http://processors.wiki.ti.com/index.php/AM335x_Power_Management_Standby_User%27s_Guide

Is the important link.  But first I had to load the 6.0 SDK version onto the BBB and power the device from the barrel jack.  For some reason it won't boot without the usb plugged in but whatever at least it's progress. I have it down to 25mA@5V on standby. Which isn't bad.  Still not as advertised.  Plus using the dying 3.2 linux kernel is a bit of a pain.

I had to do this for standby:

mkdir -p /debugfs
   mount -t debugfs debugfs /debugfs
   cd /debugfs/omap_mux/board/
   echo uart0_rxd.gpio1_10=0x27,rising > standby_gpio_pad_conf
   echo standby > /sys/power/state

cd /debugfs/omap_mux/board/suspend_io_pad_conf

echo 1 > enable*

echo xdma_event_intr0.gpio0_19=0x27 > suspend_pad_conf

echo xdma_event_intr1.gpio0_20=0x27 > suspend_pad_conf

Much of this is extracted from here also here and here.  To save you the trouble and provide what I think is useful here is a summary of the command line stuff you can do and eventually from c/c++.

Note: I found that I had a kernel dated 2013-06-20, I have updated to one from 2013-09-12.

First we will check out the frequency scaling.  Look under:

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq 
echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

cpufreq-set --governor ondemand
cpufreq-set --governor powersave




 Check out all of the different file contents there. By default the frequency scales with demand from 300kHz all the way to 1Ghz.  This brought my device's usage from 250mA down to about 120mA with only the debug serial connected and powered from the barrel plug.

Checking voltages:

cat /sys/class/regulator/regulator.3/microvolts 

It would be very nice to put the device in standby but short of recompiling the kernel with the appropriate flags I cant seem to access these features. (It seems you need this enabled in your kernel which it is not in the default one from BBB) To do this try:

mkdir /debug
mount -t debugfs debugfs /debug
echo mem > /sys/power/state 

There are other modes you can pass to state such as standby

Turning off leds.  This did not have much effect.

echo none > /sys/class/leds/beaglebone\:green\:usr0/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr1/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr2/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr3/trigger