Power measurement with BayLibre’s ACME cape

When working on optimizing the power consumption of a board we need a way to measure its consumption. We recently bought an ACME from BayLibre to do that.

Overview of the ACME

The ACME is an extension board for the BeagleBone Black, providing multi-channel power and temperature measurements capabilities. The cape itself has eight probe connectors allowing to do multi-channel measurements. Probes for USB, Jack or HE10 can be bought separately depending on boards you want to monitor.

acme

Last but not least, the ACME is fully open source, from the hardware to the software.

First setup

Ready to use pre-built images are available and can be flashed on an SD card. There are two different images: one acting as a standalone device and one providing an IIO capture daemon. While the later can be used in automated farms, we chose the standalone image which provides user-space tools to control the probes and is more suited to power consumption development topics.

The standalone image userspace can also be built manually using Buildroot, a provided custom configuration and custom init scripts. The kernel should be built using a custom configuration and the device tree needs to be patched.

Using the ACME

To control the probes and get measured values the Sigrok software is used. There is currently no support to send data over the network. Because of this limitation we need to access the BeagleBone Black shell through SSH and run our commands there.

We can display information about the detected probe, by running:

# sigrok-cli --show --driver=baylibre-acme
Driver functions:
    Continuous sampling
    Sample limit
    Time limit
    Sample rate
baylibre-acme - BayLibre ACME with 3 channels: P1_ENRG_PWR P1_ENRG_CURR P1_ENRG_VOL
Channel groups:
    Probe_1: channels P1_ENRG_PWR P1_ENRG_CURR P1_ENRG_VOL
Supported configuration options across all channel groups:
    continuous: 
    limit_samples: 0 (current)
    limit_time: 0 (current)
    samplerate (1 Hz - 500 Hz in steps of 1 Hz)

The driver has four parameters (continuous sampling, sample limit, time limit and sample rate) and has one probe attached with three channels (PWR, CURR and VOL). The acquisition parameters help configuring data acquisition by giving sampling limits or rates. The rates are given in Hertz, and should be within the 1 and 500Hz range when using an ACME.

For example, to sample at 20Hz and display the power consumption measured by our probe P1:

# sigrok-cli --driver=baylibre-acme --channels=P1_ENRG_PWR \
      --continuous --config samplerate=20
FRAME-BEGIN
P1_ENRG_PWR: 1.000000 W
FRAME-END
FRAME-BEGIN
P1_ENRG_PWR: 1.210000 W
FRAME-END
FRAME-BEGIN
P1_ENRG_PWR: 1.210000 W
FRAME-END

Of course there are many more options as shown in the Sigrok CLI manual.

Beta image

A new image is being developed and will change the way to use the ACME. As it’s already available in beta we tested it (and didn’t come back to the stable image). This new version aims to only use IIO to provide the probes data, instead of having a custom Sigrok driver. The main advantage is many software are IIO aware, or will be, as it’s the standard way to use this kind of sensors with the Linux kernel. Last but not least, IIO provides ways to communicate over the network.

A new webpage is available to find information on how to use the beta image, on https://baylibre-acme.github.io. This image isn’t compatible with the current stable one, which we previously described.

The first nice thing to notice when using the beta image is the Bonjour support which helps us communicating with the board in an effortless way:

$ ping baylibre-acme.local

A new tool, acme-cli, is provided to control the probes to switch them on or off given the needs. To switch on or off the first probe:

$ ./acme-cli switch_on 1
$ ./acme-cli switch_off 1

We do not need any additional custom software to use the board, as the sensors data is available using the IIO interface. This means we should be able to use any IIO aware tool to gather the power consumption values:

  • Sigrok, on the laptop/machine this time as IIO is able to communicate over the network;
  • libiio/examples, which provides the iio-monitor tool;
  • iio-capture, which is a fork of iio-readdev designed by BayLibre for an integration into LAVA (automated tests);
  • and many more..

Conclusion

We didn’t use all the possibilities offered by the ACME cape yet but so far it helped us a lot when working on power consumption related topics. The ACME cape is simple to use and comes with a working pre-built image. The beta image offers the IIO support which improved the usability of the device, and even though it’s in a beta version we would recommend to use it.

UN climate conference: switching to “green” electricity

Wind turbines in Denmark

The United Nations 2015 Climate Change Conference is an opportunity for everyone to think about contributing to the transition to renewable and sustainable energy sources.

One way to do that is to buy electricity that is produced from renewable resources (solar, wind, hydro, biomass…). With the worldwide opening of the energy markets, this should now be possible in most parts of the world.

So, with a power consumption between 4,000 and 5,000 kWh per year, we have decided to make the switch for our main office in Orange, France. But how to choose a good supplier?

Greenpeace turned out to be a very good source of information about this topic, comparing the offerings from various suppliers, and finding out which ones really make serious investments in renewable energy sources.

Here are the countries for which we have found Greenpeace rankings:
Australia France

If you find a similar report for your country, please let us know, and we will add it to this list.

Back to our case, we chose Enercoop, a French cooperative company only producing renewable energy. This supplier has by far the best ranking from Greenpeace, and stands out from more traditional suppliers which too often are just trading green certificates, charging consumers a premium rate without investing by themselves in green energy production.

The process to switch to a green electricity supplier was very straightforward. All we needed was an electricity bill and 15 minutes of time, whether you are an individual or represent a company. From now on, Enercoop will guarantee that for every kWh we consume from the power grid, they will inject the same amount of energy into the grid from renewable sources. There is no risk to see more power outages than before, as the national company operating and maintaining the grid stays the same.

It’s true our electricity is going to cost about 20% more than nuclear electricity, but at least, what we spend is going to support local investments in renewable energy sources, that don’t degrade the fragile environment that keeps us alive.

Your comments and own tips are welcome!

The Bifferboard: tiny, low power embedded x86 board

A nice, cheap and tiny x86 embedded board that runs Linux and just consumes 1W. It has all the basic connectivity you need in an embedded system.

As you may already know, we maintain a list of attractive and Linux friendly embedded boards. Whenever we find a new board that is attractive and meets our strict criteria (supporting Linux or other free kernels, public pricelist, public documentation and website with an English version), we add this board to our list. This way, we don’t forget about any useful board, and we can offer useful guidance to our customers and to any embedded system developer looking for a suitable hardware platform.

Somebody at Bifferos.com has just contacted us to let us know about their Bifferboard product. Here are its announced features:

  • Bifferboard150MHz RDC CPU, Intel 486SX compatible
  • 1 watt power consumption (200mA @5v)
  • 68mm x 28mm x 19mm
  • 32MB SDRAM/1MB Flash
  • OHCI/EHCI USB 2.0
  • 10/100 Ethernet
  • Serial console 115200 baud
  • 4-pin JTAG (can be used as GPIO)
  • 2 GPIO (1 LED, 1 button)
  • Linux 2.6.27.5 + OpenWrt
  • 29 UK pounds

The board has two components: the CPU board, and the I/O one, offering Ethernet and USB host connectivity. For a serial port, you can order a special cable from their shop, which connects to a USB port on your workstation.

Thanks to its low power consumption, the Bifferboard can even be powered by USB. According to its makers, the board can do anything a NSLU2 device can do. It is just cheaper (approximately 33 EUR at the time of this writing).

Last but not least, most Bifferboard hardware can be emulated with QEMU.

While it could also be suitable for mass production projects, it can be at least a nice platform for prototypes, hobby, research and educational projects.

Of course, if you know about other attractive boards that we could add to our list, please post a comment or send us e-mail.

Embedded Linux and Ecology

Embedded Linux contributions to the Linux Ecology HOWTO.

Free Electrons has contributed major updates to the Linux Ecology HOWTO, a Linux Documentation Project document that gathers ideas and techniques for using Linux in an environmentally friendly way.

In particular, Free Electrons took advantage of its experience with embedded Linux system development to add new techniques which can reduce power consumption or make it possible to extend the lifetime of old systems with limited resources.

Free Electrons also contributed an overview presentation on this HOWTO. The latest HOWTO version with our updates (waiting for the next official release) can also be found on the same page.