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ARM Energy Probe 3 Channel

The Energy Probe is a low impact, inexpensive solution to give application and system software developers quick feedback on the impact of their code on the system energy footprint. It is intended to provide a better understanding of the static and dynamic behavior of the target system for the purposes of debugging, profiling, and analysis. It is not intended to be a high-precision data acquisition instrument for power benchmarking.

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Features

To capture energy data, you must have either an Arm Energy Probe or a supported NI DAQ device.

Note

Power profiling is a deprecated feature, and is being removed from Streamline in a future version.

The Energy Probe is a low impact, inexpensive solution to give application and system software developers quick feedback on the impact of their code on the system energy footprint. It is intended to provide a better understanding of the static and dynamic behavior of the target system for the purposes of debugging, profiling, and analysis. It is not intended to be a high-precision data acquisition instrument for power benchmarking.

The Energy Probe has three power connectors, each of which is designed to connect to a 2-pin header for measuring the power. Having three power connectors allows the energy probe to provide three independent power, current, or voltage measurements.

Energy Probe schematic

Figure 1. Energy Probe schematic

In addition to the three power connectors, the Energy Probe has a single pin GND connector that must be connected to ground on your target board. It provides a ground connection for the Energy Probe.

Each of the three power connectors measures:

  • The current flow through a shunt resistor of a known value on your target system
  • The voltage at the positive terminals of the Energy Probe.

Energy Probe electrical connection example

Figure 2. Energy Probe electrical connection example

CAUTION
The Energy Probe has flying leads and must be carefully connected to your target. Do not plug the green ground wire into anything but the target ground. Do not plug it into the I/O pins or power pins. Doing so could damage your Energy Probe or the power supply of your target.

Requirements

There are several hardware and software requirements when using the Energy Probe.

Note

Power profiling is a deprecated feature, and is being removed from Streamline in a future version.

The Energy Probe has the following requirements:

  • An installation of ArmĀ® Development Studio.
  • A valid Arm Development Studio license.
  • A target running Linux kernel version 3.4 or later, configured for Streamline profiling.
  • An Energy Probe unit.
  • USB drivers for the Energy Probe.
  • A target that has 2-pin IDC 0.1″ power measurement headers. The target also requires a shunt resistor with a supply voltage less than 15V and rated at least 0.5W. The shunt resistor needs a 1-pin IDC ground terminal and must not drop more than 165mV.

Shunt resistor selection

With 20x amplification, Energy Probe requires the correct selection of a shunt resistor to provide the best possible dynamic range in power measurement, while avoiding saturation of the input of Energy Probe.

Note

Power profiling is a deprecated feature, and is being removed from Streamline in a future version.

A shunt resistor with a value that is too low reduces measurement dynamic range, resulting in less resolution in the power data. A shunt resistor with a value that is too high can cause the input stage of the Energy Probe to saturate, which causes a flat line in the charts that are related to Energy Probe in the Timeline view.

To avoid input saturation, the drop across the shunt resistor must never be more than 165mV. You can also use the following equation to determine whether your shunt resistor is appropriate:

RShunt(max) = 165 x Vsupply / ( 1000 x Power )

Vsupply is the input voltage. Power(max) is the maximum power that the Energy Probe measures. Rshunt(max) is the maximum value of the shunt resistor. A shunt resistor value that is greater than Rshunt(max) might cause input saturation.

This equation provides the absolute maximum value for the shunt resistor. Use a value that is at least five percent lower than this maximum to allow for component tolerances.

Note

When connecting the Energy Probe, consider the following:

  • The black and white probe closest to the green wire is Channel 0.
  • For best results, attach Channel 0 to the power source which best represents the CPU load. Streamline aligns the power data with the software activity by maximizing the correlation of Channel 0 with the CPU load.
  • The probe white wire is V+. The black wire is V-.
Examples
  • 5V power supply, 8W(max), Rshunt(max) = 100 milliohms.
  • 1V core voltage, 2.5W(max), Rshunt(max) = 50 milliohms.
  • 1.5V core voltage, 0.4W(max), Rshunt(max) = 500 milliohms.

Setting up

It is critical that you set up your Energy Probe correctly. Failure to do so can result in missing power data in Streamline, and even damage to your target.

About this task
Note

Power profiling is a deprecated feature, and is being removed from Streamline in a future version.

Procedure
  1. Connect your target to your host through a USB port.
  2. If necessary, install drivers using the standard Windows driver installation.

    When first plugging in the Energy Probe on Windows, the LED flashes RED at approximately one second intervals. These red flashes indicate that the USB enumeration has failed and that you must install the driver.

  3. If you are prompted to locate the driver file, select the ARM_EnergyProbe.inf configuration file, which is located in <DS_install_directory>/sw/streamline/energy_meter/energy_probe/.

    When you have installed the drivers, and Energy Probe is operating correctly, the LED remains green.

  4. To set it up on Linux Ubuntu, enter the following command:
  • sudo apt-get install libudev-dev
  • On Linux Ubuntu, you must do either of the following for Energy Probe to successfully use the device:
    • Change the permissions of the TTY device by entering the following command:
  • chmod 777 <tty_location>
  • Add yourself to the same group as the TTY device by entering the following command:
    • usermod -a -G <Group_Name User_Name>

    dialout is the usual name of the group for the TTY device.

    If you attach a probe to the target with the channel wire connector the wrong way around, the LED turns red and blinks. Connecting the channel wire the wrong way round does not damage your target or the Energy Probe but it does not provide useful data. Disconnect all Energy Probes and wait until the LED changes to green. Then reattach them one by one and make sure that you reverse any probe that caused the LED to change to red. When you have attached the Energy Probe correctly, the LED remains green.

    Note

    If there is low consumption, it is possible that the LED remains red even if the connection is correct. For example, the LED might remain red if the target device is idle.

  • If your target has headers available for power or energy metering, attach the ground wire, then attach the probes.
  • Attach the probes.

    Make sure that the probe polarity is correct by observing whether the LED changes from green to red. The probe white wire is V+. The black wire is V-.

Results

ARM Energy Probe 3 Channel
ARM Energy Probe 3 Channel connected to development board

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