## Power Measurement

Power usage can be measured via two methods on the Summit SOM 8M Plus DVK:

• Externally via a digital multimeter
• Programmatically from the on-board power monitoring IC

Both of these methods can be used to measure power for either the SOM itself or an externally connected battery (connector J7).

### Current Sense Resistor

The Summit SOM 8M Plus DVK is equipped with a pair of 0.033 Ohm current sense resistors: R272 which is located inline with the SOM (VSYS_5V) power rail to the SOM 8M Plus itself and R266 which is located inline with the external battery power rail. By measuring the voltage drop across test points TP66 and TP67 for the SOM power rail and test points TP65 and TP64 for the external battery power rail, the current (and therefore also the power) used can be calculated.

Measurement Type Current Sense Resistor Test Points Current Calculation Formula
SOM Power Rail R272 TP66 (-) and TP67 (+) $I_{SOM}=\frac{V_{R272}}{0.033\Omega}$
External Battery Power Rail R266 TP65 (-) and TP64 (+) $I_{Batt}=\frac{V_{R266}}{0.033\Omega}$

From here, the power can also be easily calculated since the voltage is known.

For example, a measured voltage drop of 12mV on R272 would correlate to a current draw of ~364mA and a power usage of ~1.82W:

$I_{SOM}=\frac{12mV}{0.033\Omega}=\:&space;\sim364mA$

$P_{SOM}=5V\times\:&space;\sim364mA=\:&space;\sim1.82W$

### On-board Power Monitor IC (Microchip PAC1932)

The Summit SOM 8M Plus DVK includes an onboard power monitoring IC (a Microchip PAC1932) which can be used to measure the current draw on the SOM (VSYS_5V) power rail and an externally connected battery (J7). To read either current, issue the corresponding command below:

SOM Power Rail:

cat /sys/bus/iio/devices/iio\:device0/in_current0_input


Battery:

cat /sys/bus/iio/devices/iio\:device0/in_current1_input


From here, the power can also be easily calculated since the voltage is known.

## Entering / Exiting Suspend

### Entering Suspend

To place the Summit SOM 8M Plus into suspend, issue the following command:

systemctl suspend


The SOM will gracefully suspend all relevant subsystems and enter a low power state until woken up by an appropriate signal.

### Exiting Suspend

There are a number of available methods to wake the SOM back up from suspend:

• Wake on LAN
• Wake on wireless
• The CPU ON/OFF signal (mapped to switch S2 on the DVK board)
• The Messaging Unit (MU) peripheral (used to communicate between the A53 cores and the M7 core)