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Measuring Power on the OMAP35x EVM
A simple way to take quick power measurements on the OMAP35x EVM is to use a multimeter to measure the voltage drop across the jumpers J5, J6, and J9. Doing this will provide an instantaneous power measurement and is a good representation of the power consumed in a scenario where the power profile is relatively flat. For scenarios where power changes drastically a multimeter might not present the full power picture. For such cases you will need a more sophisticated tool that can obtain and record several voltage readings over time. For tools with their own built-in current measuring shunt resistors, you could remove the resistors on the EVM.
The power rails on the EVM
The EVM has three separate power rails: processor rail, interconnects and peripherals rail, and the EVM 1.8 rail. Each can be measured by measuring the voltage on the specific jumper assigned to that particular rail. The table below describes which jumper corresponds to which rail. The picture will give you an idea of the location of the jumpers for each rail.
|I-Connects / Peripherals||J5|
The following steps describe how to take the measurements on the board and calculate the power.
- Measure voltage drop across the jumper pins.
- Calculate the current being consumed by dividing the measured voltage drop by the resistance in parallel with the jumper pins.
- Measure the voltage seen by the OMAP pin by measuring the voltage from the jumper pin tied to the OMAP side of the series resistor to ground on the board.
- Calculate power by multiplying the current from step 2 by the voltage in step 3.
This procedure can be used to measure the following rails on OMAP35x:
- VDD1/vdd_mpu_iva – the processors power supply rail. Do this on J6.
- VDD2/vdd_core – the interconnects and peripherals supply rail. Do this on J5.
- EVM 1.8V - note that this includes not just OMAP35x 1.8V rails, but also other devices on the EVM. Do this on J9.
As the equations in green above show, the current is calculated by dividing the measured voltage drop over the jumper by the small resistor value on the EVM.