Some MSP430 launchpads such as the MSP430FR4133 LaunchPad include the so-called "EnergyTrace™ technology". It consists of a software-controlled DC-DC converter that can measure the energy it is delivering. Looks like TI has patents on that: US20130154594, US20140253096

The "official" way to make use of this feature is TI's "Code Composer Studio" IDE. Since I don't use CCS, installing CCS just for measuring current consumption seems a bit silly. Fortunately there's a better way: TI provides an open-source library for communicating with some of their MSP430 programmers. As well as debugging control and programming the library also gives access to the EnergyTrace feature. So I wrote a small program based on an example that reads the EnergyTrace measurements.

Output Format

Data is written to stdout in 4 columns:

1. Time in seconds
2. Current in amps
3. Voltage in volts
4. Energy in Joules

Debug information gets prefixed with a #, so it gets ignored by gnuplot and the like. For some reason, differentiating and low-pass filtering the energy measurements leads to more accurate readings than the current measurement itself.

Dependencies

You'll need MSP430 debug stack (libmsp430.so) and the usual things like make and gcc. Unfortunately, building the MSP430 debug stack is a bit difficult at this time since it's missing some #include and triggers a compiler bug. Using Arch Linux? You're lucky, I've created a PKGBUILD and patches for easy installation: aur-mspds At the time of writing, the AUR package mspds is broken.

How do I build and run?

$ make
$ ./energytrace <measurement duration in seconds> > energytrace.log

Use you favourite tool for visualizing and processing the recorded data.

$ gnuplot

        G N U P L O T
        Version 5.2 patchlevel 2    last modified 2017-11-01 

        Copyright (C) 1986-1993, 1998, 2004, 2007-2017
        Thomas Williams, Colin Kelley and many others

        gnuplot home:     http://www.gnuplot.info
        faq, bugs, etc:   type "help FAQ"
        immediate help:   type "help"  (plot window: hit 'h')

Terminal type is now 'qt'
gnuplot> plot "energytrace.log" 
gnuplot> 

Conclusion

EnergyTrace comes in really handy for measuring the power consumption of MCUs as it saves you from fiddling with current shunts, differential amplifiers and oscilloscopes. Event when you're just using EnergyTrace, the MSP430FR4133 LaunchPad is pretty good value at $14.

This little program has proven to be useful during the development of pluto.