Using the Energy Probe
ARM DUI 0482K Copyright © 2010-2012 ARM. All rights reserved. 12-3
ID120712 Non-Confidential
12.2 Energy Probe requirements
The Energy Probe has the following requirements:
• An installation of ARM DS-5 Basic or Professional Edition, version 5.9 or later.
• A suitable DS-5 license.
• A Streamline-enabled target. For Linux and Android targets, this requires the gator driver
and daemon to be installed on the target.
• An Energy Probe Unit.
• A USB extension cable.
• 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.
You can tell if your target has the right power management headers by visual inspection.
For more information about whether or not your target meets the other requirements for
Energy Probe, see the documentation for your target.
12.2.1 Precautions
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. This includes I/O pins and power
pins. Doing so could cause damage to your Energy Probe or the power supply of your target.
12.2.2 Determining the optimal shunt resistor value
With 20x amplification, Energy Probe requires 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. A shunt resistor with a value too low reduces measurement dynamic range,
resulting in less resolution in the power data. A shunt resistor with a value too high can cause
the input stage of the Energy Probe to saturate, which causes a flat line in the charts related to
Energy Probe in the Streamline Timeline view.
To avoid input saturation, the drop across the Rshunt resistor must never be more than 165mV.
You can also use the following equation to determine if your shunt resistor is appropriate:
RShunt(max) = 165 x Vsupply / ( 1000 x Power )
Vsupply
is the input/core 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 greater
than
Rshunt(max)
might cause input saturation.
This equation provides the absolute maximum value for Rshunt. Use a value that is more than
five percent lower than this value to allow for component tolerances.
Examples
• 5V power supply, 8W(max), Rshunt(max) = 100mOhm
• 1V core voltage, 2.5W(max), Rshunt(max) = 50mOhm
• 1.5V core voltage, 0.4W(max), Rshunt(max) = 500mOhm.
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