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page.title=Power consumption
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<h2>In this document</h2>
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<h2 id="low_power_sensors">Low-power sensors</h2>
<p>Some sensor types are defined as being low power. Low-power sensors must
function at low power, with their processing done in the hardware. This means
they should not require the SoC to be running. Here are some low-power sensor
<li> Geomagnetic rotation vector </li>
<li> Significant motion </li>
<li> Step counter </li>
<li> Step detector </li>
<li> Tilt detector </li>
<p>They are accompanied by a low-power (<img src="images/battery_icon.png"
width="20" height="20" alt="Low power sensor" />) icon in the <a
href="sensor-types.html#composite_sensor_type_summary">Composite sensor type
summary</a> table.</p>
<p>These sensor types cannot be implemented at high power as their primary benefit
is low battery use. These sensors are expected to be activated for very long
periods, possibly 24/7. It is better to not implement a low-power sensor at all
rather than implement it as high power, as it would cause dramatic battery
<p>Composite low-power sensor types, such as the step detector, must have their
processing conducted in the hardware.</p>
<p>See the CDD for specific power requirements, and expect tests in CTS to
verify those power requirements.</p>
<h2 id="power_measurement_process">Power measurement process</h2>
<p>The power is measured at the battery. For values in milliWatts, we use the
nominal voltage of the battery, meaning a 1mA current at 4V must be counted as
<p>The power is measured when the SoC is asleep, and averaged over a few seconds
of the SoC being asleep, so that periodic spikes in power from the sensor chips
are taken into account.</p>
<p>For one-shot wake-up sensors, the power is measured while the sensor doesnt
trigger (so it doesnt wake the SoC up). Similarly, for other sensors, the
power is measured while the sensor data is stored in the hardware FIFO, so the
SoC is not woken up.</p>
<p>The power normally is measured as a delta with when no sensor is activated.
When several sensors are activated, the delta in power must be no greater than
the sum of the power of each activated sensor. If an accelerometer consumes
0.5mA and a step detector consumes 0.5mA, then activating both at the same time
must consume less than 0.5+0.5=1mA.</p>