Measuring Power Values
Device manufacturers must provide a component power profile in /frameworks/base/core/res/res/xml/power_profile.xml.
To determine values for power profiles, use hardware that measures the power being used by the device and perform the various operations for which information is needed. Measure the power use during those operations and compute the values (deriving differences from other baseline power uses as appropriate).
As the goal of a power profile is to estimate battery drain appropriately, power profile values are given in current (amps). The Android framework multiplies the current by the time for which the subsystem was active and computes the mAh value, which is then used to estimate the amount of battery drained by the application/subsystem.
Devices with running Android 6.0 and higher can provide additional power values obtained from chipset data.
Devices with heterogeneous CPUs
The power profile for devices with CPU cores of heterogeneous architecture must include the following additional fields:
- Number of total CPUs for each cluster (expressed in cpu.clusters.cores).
- CPU speeds supported by each cluster.
- Active CPU power consumption for each cluster.
To differentiate between active CPU power consumption and supported CPU speeds for clusters, append the cluster number to the name of the array. Cluster numbers are assigned in the order of CPU cores in the kernel device tree. For example, in a heterogeneous architecture that has two (2) clusters with four (4) cores:
- cluster0 consists of cpu0-3
- cluster1 consists of cpu4-7
The Android framework uses these CPU core numbers when it reads statistics from the sysfs files in: /sys/devices/system/cpu/cpu<number>/cpufreq/stats.
Example of cluster CPUs and speeds:
200 300 400 600000 800000 1200000 400 500 600 800000 1200000 1400000
Power values
The following table describes available power value settings. To view the sample file in AOSP, see .
| Name | Description | Example Value | Notes |
|---|---|---|---|
| none | Nothing | 0 | |
| screen.on | Additional power used when screen is turned on at minimum brightness. | 200mA | Includes touch controller and display backlight. At 0 brightness, not the Android minimum which tends to be 10 or 20%. |
| screen.full | Additional power used when screen is at maximum brightness, compared to screen at minimum brightness. | 100mA-300mA | A fraction of this value (based on screen brightness) is added to the screen.on value to compute the power usage of the screen. |
| bluetooth.active | Additional power used when playing audio through Bluetooth A2DP. | 14mA | |
| bluetooth.on | Additional power used when Bluetooth is turned on but idle. | 1.4mA | |
| wifi.on | Additional power used when Wi-Fi is turned on but not receiving, transmitting, or scanning. | 2mA | |
| wifi.active | Additional power used when transmitting or receiving over Wi-Fi. | 31mA | |
| wifi.scan | Additional power used when Wi-Fi is scanning for access points. | 100mA | |
| dsp.audio | Additional power used when audio decoding/encoding via DSP. | 14.1mA | Reserved for future use. |
| dsp.video | Additional power used when video decoding via DSP. | 54mA | Reserved for future use. |
| camera.avg | Average power use by the camera subsystem for a typical camera application. | 600mA | Intended as a rough estimate for an application running a preview and capturing approximately 10 full-resolution pictures per minute. |
| camera.flashlight | Average power used by the camera flash module when on. | 200mA | |
| gps.on | Additional power used when GPS is acquiring a signal. | 50mA | |
| radio.active | Additional power used when cellular radio is transmitting/receiving. | 100mA-300mA | |
| radio.scanning | Additional power used when cellular radio is paging the tower. | 1.2mA | |
| radio.on | Additional power used when the cellular radio is on. Multi-value entry, one per signal strength (no signal, weak, moderate, strong). | 1.2mA | Some radios boost power when they search for a cell tower and do not detect a signal. Values can be the same or decrease with increasing signal strength. If you provide only one value, the same value is used for all strengths. If you provide two values, the first is used for no-signal, the second value is used for all other strengths, and so on. |
| cpu.speeds | Multi-value entry that lists each possible CPU speed in KHz. | 125000KHz, 250000KHz, 500000KHz, 1000000KHz, 1500000KHz | The number and order of entries must correspond to the mA entries in cpu.active. |
| cpu.idle | Total power drawn by the system when CPUs (and the SoC) are in system suspend state. | 3mA | |
| cpu.awake | Additional power used when CPUs are in scheduling idle state (kernel idle loop); system is not in system suspend state. | 50mA | Your platform might have more than one idle state in use with differing levels of power consumption; choose a representative idle state for longer periods of scheduler idle (several milliseconds). Examine the power graph on your measurement equipment and choose samples where the CPU is at its lowest consumption, discarding higher samples where the CPU exited idle. |
| cpu.active | Additional power used by CPUs when running at different speeds. | 100mA, 120mA, 140mA, 160mA, 200mA | Value represents the power used by the CPU rails when running at different speeds. Set the max speed in the kernel to each of the allowed speeds and peg the CPU at that speed. The number and order of entries correspond to the number and order of entries in cpu.speeds. |
| cpu.clusters.cores | Number of cores each CPU cluster contains. | 4, 2 | Required only for devices with . Number of entries and order should match the number of cluster entries for the cpu.active and cpu.speeds. The first entry represents the number of CPU cores in cluster0, the second entry represents the number of CPU cores in cluster1, and so on. |
| battery.capacity | Total battery capacity in mAh. | 3000mAh |
Devices with Bluetooth and Wi-Fi controllers
Devices with Bluetooth and Wi-Fi controllers running Android 6.0 and higher can be polled for the following energy use data:
- Time spent transmitting (in milliseconds).
- Time spent receiving (in milliseconds).
- Time spent idle (in milliseconds).
Time values are not measured but are instead available from respective chip specifications and must be explicitly stated (for details, see ). To convert time values to power values, the framework expects four (4) values for each controller in a resource overlay at /frameworks/base/core/res/res/values/config.xml.
| Controller | Values/Resource Names | Description |
|---|---|---|
| Bluetooth | android:integer/config_bluetooth_idle_cur_ma | Average current draw (mA) of the Bluetooth controller when idle. |
| android:integer/config_bluetooth_active_rx_cur_ma | Average current draw (mA) of the Bluetooth controller when receiving. | |
| android:integer/config_bluetooth_tx_cur_ma | Average current draw (mA) of the Bluetooth controller when transmitting. | |
| android:integer/config_bluetooth_operating_voltage_mv | Average operating voltage (mV) of the Bluetooth controller. | |
| Wi-Fi | android:integer/config_wifi_idle_receive_cur_ma | Average current draw (mA) of the Wi-Fi controller when idle. |
| android:integer/config_wifi_active_rx_cur_ma | Average current draw (mA) of the Wi-Fi controller when receiving. | |
| android:integer/config_wifi_tx_cur_ma | average current draw (mA) of the Wi-Fi controller when transmitting. | |
| android:integer/config_wifi_operating_voltage_mv | Average operating voltage (mV) of the Wi-Fi controller. |