Kees Verruijt is a sailing software engineer from Harlingen, NL. He
maintains CANboat, which he describes as "[a] small but effective
set of command-line utilities to work with CAN networks on BOATs".
By Femnett/Maretron, LLP (Maretron, LLP) CC BY 2.5, via Wikimedia Commons
To help you understand a bit more about the technology on top of which
CANboat works, we have provided a brief explanation below. The
following text has been adapted from the CAN bus article on
English Wikipedia (which was originally licensed under the terms of
the Creative Commons Attribution-ShareAlike 3.0 License):
A Controller Area Network (CAN bus) is a vehicle bus standard
designed to allow microcontrollers and devices to communicate with
each other without a host computer or server. It is a message-based
protocol that was designed originally for multiplex electrical
wiring within automobiles. Modern automobiles may have as many as 70
electronic control units (ECU) for various subsystems. Others are
used for transmission, airbags, antilock braking/ABS, cruise
control, electric power steering, audio systems, power windows,
doors, mirror adjustment, battery and recharging systems for
hybrid/electric cars, etc. Some of these form independent
subsystems, but communications among others are essential. A
subsystem may need to control actuators or receive feedback from
sensors. The CAN standard was devised to fill this need. The use of
CAN was adopted by the marine industry, because they also needed a
plug-and-play communications standards used for connecting marine
sensors and display units within ships and boats.
Could you provide a little info to landlubbers about the kinds of electronics and computers used in the marine world?
Marine electronics has a long history, it was way back in the 1960s
when electronics were starting to make an appearance on recreational
and commercial boats. Depth sensors, marine radios, wind sensors and
geo-location devices were appearing on the market. In the beginning
every manufacturer started creating their own networks, usually based
on some variation of serial data, typically running at 4800 or 9600
baud. Electronic sensors enabled boaters to have displays with data
such as compass heading, wind and boat speed. Two other major
developments were the first auto-pilots (a device that keeps the boat
on a particular heading) and position locators -- first based on land
based radio signals and later on satellite radio signals. As you can
imagine knowing where you are is much harder for a sailor than a
landlubber as there are so few reliable points of reference out on the
ocean! One of the first applications for a protocol used by devices
made by different manufacturers was to pass heading data from the
sensor network or from the satellite navigator to the auto-pilot.
The need for industry data standards lead to a group of US electronics
dealers forming the National Maritime Electronics Association (NMEA),
which interacted with the various manufacturers to standard protocol
and data formats for devices. Membership for these manufacturers meant
access to the large single US market, so soon manufacturers from
Europe and Australia/New Zealand joined as well. In the 1980s this
resulted in the NMEA 0180 and later 0183 standard. This standard is
used every day by billions of users as (almost) all modern satellite
navigation building blocks will transmit data using this protocol.
As the number of devices on board started to rise and new sensors and
displays were added the manufacturers saw that a new standard would be
needed. Like most such standard committees they chose a name that
would reflect the hoped-for release year, so NMEA 2000 came to be. It
took a few years more before the first NMEA 2000 devices to come to
market, but today they're everywhere. NMEA 2000, or N2K, is based on
CANbus. Development for CANbus was started by Bosch for use in
the car industry, but it was soon adopted by many other industries as
well. The marine version communicates at 250,000 baud, and allows you
to hook up many devices to a single "backbone" meandering through your
ship. Electrically its really neat -- no master device, no wasted
bandwidth with high priority messages automatically taking
precedence. The datagrams are easier to generate and parse in small
microcontrollers as the format is in binary, with fixed bit length
fields. In other words, when done correctly they map one-on-one to a C
structure with the fields in a native C unsigned or signed integer
value. This also has the effect of the data being harder to understand
if you don't have access to the standard.
Where does CANboat fit into all this?
Use of the NMEA 2000 standard is encumbered by onerous copyright
restrictions. The original documents are under copyright, and no
member NMEA is allowed to publish them, not even in a different
format. This resulted in manufacturers documenting just the list of
sentences that their devices support. The NMEA nowadays does provide a
list of all messages and what fields they contain, but not the
precision or meaning of these fields.
CANboat gets around this by being written using only public sources,
without access to the standard itself. The technical detail of which
fields take up how many bits and what the used precision is was
reverse engineered from live networks.
Nowadays CANboat is the only comprehensive NMEA 2000 database
available in a free format. It also contains programs that can be used
to read N2K data from the bus, convert it into text, XML or JSON and
pass it on to other software.
What inspired you to create CANboat?
As I was building a new boat in 2008-2010 I wanted to have a single
device that would show all the data available on board via a simple
Web interface. I could join the NMEA and buy the NMEA 2000 standard
(spending $3,000 USD or so) but then I couldn't actually release my
program as free software. So I figured that the only way out was to
reverse engineer the protocol from scratch. It took me about a week to
write some code to interact with a CAN interface and only a few
evenings before I had the first datagram done.
Soon I was able to have my dream of a tablet-friendly, HTML5(ish)
page, in 2010. It took many evenings though over the last 6 years to
add more and more N2K datagrams. Luckily, after making the sources GPL
and putting them on Github I soon got a few collaborators from around
the globe. All regular non-company specific NMEA 2000 messages are
now decoded, most of them completely. CANboat is unique in that it
also decodes. It is able to direct quite a number of company specific
messages, but work on this is particularly slow as it requires a
software developer with both access to a device producing them, a
(perceived) need to use them and the will to put in hard hours doing
the reverse engineering. This involves looking at hex dumps and
fiddling until it makes sense.
How are people using it?
This has changed over time. In the early days everyone in the Marine
Electronics community loved the idea but didn't necessarily use it --
partly because you need to have N2K on board. Andrew Mason of the
University of Auckland, N.Z., was one of the first who grasped what I
was doing and he created OpenSkipper using the CANboat database, and
others soon joined.
Nowadays it is used by hobbyists (usually professional software
developers with a boat) to monitor their onboard devices. And some
even use it to control stuff -- for example turning a water maker off if
the shore power fails or the generator shuts down. I use it myself to
infer the boat's navigation status and automatically switch on the correct
navigation lights. It uses the anchor winch state, engine RPM and GPS
location to decide what lights should be on and which should be off.
CANboat is also used by people in the marine electronics industry --
software developers and hardware developers that are either
contemplating entering the marine electronics world and are not yet
NMEA members or haven't bought the standard yet. It is also used by
companies that do have the standard but use it as a "lab instrument"
to see what is going on and log data produces by new devices under
development.
Probably the biggest set of users are those using it to feed NMEA 2000
data into Signal K servers. Signal K is probably even more
exciting than CANboat. It is the outcome of an association of
frustrated software developers who felt it was time for a completely
new free standard for marine electronics, based on the ideas of
"internet of things" and oriented towards reusing standards such as
TCP, WS and JSON.
What features do you think really sets CANboat apart from similar software or projects (if there are any similar projects!)?
There are a few other projects that contain N2K parsers, but the ones
that I have seen cater more towards very small microcontrollers, and
focus on the most used data sentences only. CANboat is the only one
with the ambition to cover all messages, and to cover company specific
messages.
Why did you choose the GNU GPL version 3 (or later) as the license for CANboat?
I personally think the RFC method of publishing standards is a better
one than the ISO/IEC style of charged access. I also don't like how
the NMEA uses copyright law to prevents people with access to the
standard to talk about content within the standard. Even the IEC
doesn't do this. When I decided to make my work free software, I felt
that I wanted to help non-professionals to gain access, but I also
wanted to respect the NMEA as much as possible. I'm not trying to
subvert their business model here, just offering an alternative for
free software development. What I didn't want to see happening is that
business would just use my work as a means to evade paying the NMEA
without them contributing back to the community. This is why I made a
deliberate choice for the GPL with its strong copyleft clause, which
ensures this.
How can users (technical or otherwise) help contribute to CANboat?
If you've installed CANboat and you get "unknown PGN" messages you
should, at the very least, create an issue on Github to make us aware
of this. We can then decide to add at least minimal support for
these. What would be even better is that you exercise the device that
emits the PGNs and do the reverse engineering yourself. This is
especially true if the PGNs are in the "company specific" range, as
these tend to be hard for others to analyze if they don't have access
to a live device.
Over the last five years the amount of community updates has steadily
increased, so I'm not complaining, but this is still a
mostly-one-person-effort right now.
What's the next big thing for CANboat?
The next big thing is support for Signal K. This is a brand new set of
Internet age message and server specifications. If you are a marine
electronics enthusiast that wants to build your own sensors and
connect those into a network, you should not use NMEA 0183 or NMEA
2000, but Signal K. If you are a software enthusiast that wants to
experiment with the data available on your NMEA 2000 network, by all
means use CANboat, but use it to feed data into a Signal K server, and
then use the Signal K data.
As Signal K is a work that stands on its own and does not require the
use of either NMEA 0183 or 2000 it can be the next generation protocol
for marine data interchange. This has been recognized by the NMEA as
well, who now recommend the use of Signal K when creating new products
that communicate over TCP/IP. Signal K code is Apache licensed and
protocols and databases are CC BY-SA licensed.
Enjoy this interview? Check out our previous entry in this series, featuring Matt Lee of GNU Social.
