I have instaled Ubuntu 11.10 on BB-XM and I measured power consumption while running a video decode.
First I configured MADC with i2c (as said on: https://groups.google.com/forum/?fromgroups#!topic/beagleboard/8PqigpF1VEk by horse_dung)
turn on MADC and connect the ADC pins…
i2cset -y -f 1 0x4a 0x00 0x01
i2cset -y -f 1 0x48 0xbb 0x08
set which ADCs to read/average
i2cset -y -f 1 0x4a 0x06 0x28
i2cset -y -f 1 0x4a 0x07 0x00
i2cset -y -f 1 0x4a 0x08 0x28
i2cset -y -f 1 0x4a 0x09 0x00
start read and get results
i2cset -y -f 1 0x4a 0x12 0x20
i2cget -y -f 1 0x4a 0x3d w
i2cget -y -f 1 0x4a 0x41 w
In example, I got two values
then I turned it on decimal and divided by 64 and then by 1024 (because it is 10-bit res.). Multiplying then by 2.5 I got the voltages (dynamic range of the ADCs are 2.5V)
50624/64-> /1024 → *2.5
51520/64-> /1024 → *2.5
as said on the xm manual, that value is 46% of the voltage
so, multiplied by 2.17, I got those values:
to get the drop of current, I made (value2 - value1)/0.1R.
(4.264 - 4.19)/0.1 = 0,741699 → 741mA
Finally, with P = V * I
I get, for example
P = 5 * 0,741 = ~3,7 W
Well, is that process correct?
The values I get, by looping the (#start read and get results) process in a 0.5s with cpufreq-set at 300 MHz and then at 800MHz
shows minimal diference. Somebody made similar tests to compare the results?
In the loop with a video decode on ARM get Average drop current at 614mA.
Comparing with values on Beagle C4, where the read values are
(Dec/64) (V - 5V)
adcin3 909 → 4,81574707
adcin5 913 → 4,836938477
Current= adcin5- adcin3= 211mA
That means ~2.9x more drop current on XM than C4, in that example. Is it because the USB hub integrated on the XM board?
I would appreciate some coments on that, and if someone done similar tests or to confirm those values…