Two Types of Gateways

There are two types of gateways in the IoT (Internet of Things) world.

The first is a field gateway. It’s called such because it resides in the “field” - that is it’s on location and not in the cloud. It’s in the factory or on the robot for instance. Microsoft has an open source codebase for field gateways called the Azure IoT Gateway SDK you can start with.

The second is a cloud gateway, and obviously that one is in the cloud. Microsoft has a codebase for one common cloud gateway function - protocol adaptation available at Azure IoT Protocol Gateway.

Both of these entities exist as a point of communication through which you direct your IoT traffic messages for various reasons.

You’ll also hear the term edge to refer to devices and gateways in the field. The edge is the part of an IoT solution that’s touching the actual things. In the internet of cows, it’s the device hanging on the cow’s collar. In an airliner, it’s all the stuff on the plane itself (which I realize is a confusing scenario since technically those devices may also be in a cloud).

Reasons to Use a Gateway

Some possible reasons gateways exist are…

• you need to filter the data. It may be that qualifying data deserves the trip to the cloud, but the rest just needs to be archived to local mass storage or even completely ignored.

• you need to aggregate the data. Your messages may be too granular, and what you really want to send to the cloud is a moving average, a batch of each 1000 messages, a batch of messages every hour, or something else.

• you need to react to your data quickly. It doesn’t usually take that long to get to the cloud and back, but then again “long” is relative. If you’re trying to apply the brakes in a vehicle every millisecond counts.

• you need to control costs. You can use filtering or aggregation to massage your messages before going to the cloud to reduce your costs, but there may be some other business logic you van apply to the same end.

• you have some cross cutting concerns such as message logging, authorization, or security that a gateway can facilitate or enforce.

• you need some additional capabilities. Devices that are not IP capable and able to encrypt messages are dependent on a field gateway to get any messages to the cloud. Devices that are able to speak securely to the cloud but are not for some reason capable to using one of the standard IoT protocols (HTTP, AMQP, or MQTT) require either a field gateway or a cloud gateway (such as Azure IoT Protocol Gateway).

Gateway Hardware

What kind of hardware might you end up using for a gateway? Well, the possibilities are very broad. It could be anything from a Raspberry Pi to a very expensive, dedicated gateway system.

Intel has a helpful article about field gateways and the hardware they offer. Dell has a product called the Edge Gateway 5000 that looks to me to be a pretty solid solution too.

Also, Azure maintains a big catalog of certified hardware including gateways that might be the most helpful resource.

Closing

There’s certainly a lot more about gateways to know, but I’ll leave this here now in case it helps you out.

​I’ve been hacking on the Raspberry Pi of late and wanted to share out some of the more interesting learnings.

I think people that love technology love understanding how things work. When I was a kid I took apart the family phone because I was compelled to see what was inside that made it tick. My brother didn’t care. If it made phone calls, he was fine with it. I had to understand.

Likewise, I knew that I could use a Node library and change the GPIO pin levels on my Raspberry Pi, but I wanted to understand how that worked.

In case you’re not familiar, GPIO stands for General Purpose Input/Output and is the feature of modern IoT boards that allows us to controls things like lights and read data from sensors. It’s a bank of pins that you can raise high (usually to something like 3.3V) or low (0V) to cause some electronic behavior to occur.

On an Intel Edison (another awesome IoT board), the platform developers decided to provide a C library with mappings to Node and Python. On the default Edison image, they provided a global node module that a developer could include in his project to access pins. The module, by the way, is called libmraa.

On a Raspberry Pi, it works differently. Instead of a code library, a Pi running Raspbian uses the Linux file system.

When you’re sitting at the terminal of your pi (either hooked up to a monitor and keyboard or ssh’ed in), try…

cd /sys/class/gpio

You’ll be taken to the base of the file system that they chose to give us for accessing GPIO.

The first thing to note is that this area is restricted to the root user. Bummer? Not quite. There’s a way around it.

The system has a function called exporting and unexporting. Yes, I know that unexport is not a real word, but alas I’m not the one that made this stuff up, and besides, who said Linux commands had to make sense?

To access a pin, you have to first export that pin. To later disallow access to that pin, you unexport it.

I had a hard time finding good documentation on this, but then I stumbled upon this znix.com page that describes it quite well. By the way, this page references “the kernel documentation,” but when I hit that link here’s what I get…

Oh well.

Now keep in mind that to follow these instructions you have to be root. You cannot simply sudo these commands. There is an alternative called gpio-admin that I’ll talk about in a second. If you want to just become root to do it this way, you do…

su root

If you get an error when you do that, you may need to first set a password for root using sudo passwd.

To export then, you do this…

echo <pin number> > /sys/class/gpio/export

And the pin number is the pin name - not the header number. So pin GPIO4 is on pin 7 on an RP2, and to export this you use the number 4.

When you do that, a virtual directory is created inside of /sys/class/gpio called gpio4, and that directory contains virtual files such as direction, value, edge, and active_low. These files don’t act like normal files, by the way. When you change the text inside one of these files, it actually does something - like perhaps the voltage level on a GPIO pin changes. Likewise, if a hardware sensor causes the voltage level on a pin to change, the content of one of these virtual files is going to change. So this becomes the means by which we communicate in both directions with our GPIO pins.

The easiest way, then, to read the value of the /sys/class/gpio/gpio4/value file is…

cat /sys/class/gpio/gpio4/value

Easy.

To write to the same file, you have to first make sure that it’s an out pin. That is, you have to make sure the pin is configured as an output pin. To do that, you change the virtual direction file. Like this…

echo out > /sys/class/gpio/gpio17/direction

That’s a fancy (and quick) way to edit the contents of the file to have a new value of “out”. You could just use vi or nano to edit the file, but using echo and the direction operator (>) is quicker.

Once you have configured your pin as an output, you can change the value using…

echo 0 > /sys/class/gpio/gpio4/value //set the pin low (0V)
echo 1 > /sys/class/gpio/gpio4/value //set the pin high (3.3V)

Now that I’ve described the setting of the direction and the value, you should know that there’s a shortcut for doing both of those in one motion…

echo high > /sys/class/gpio/gpio4/direction

There’s more you can do including edge control and logic inversion, but I’m going to keep this post simple and let you read about that on the znix.com page.

Now, although it’s fun and satisfying to understand how this is implemented, and it might be fun to manipulate the pins using this method, you’ll most likely want to use a language library to control your pins in your app. Just know that the Python and Node libraries that change value are actually just wrappers around these file system calls.

For instance, let’s take a look at the pi-gpio.js file in the pi-gpio module…

write: function(pinNumber, value, callback) {
	pinNumber = sanitizePinNumber(pinNumber);
	value = !!value ? "1" : "0";
	fs.writeFile(sysFsPath + "/gpio" + pinMapping[pinNumber] + "/value", value, "utf8", callback);
}

When you call the write() method in this library, it’s just calling the file system.

So there you have it. I hope you feel a little smarter.

Getting a Raspberry Pi online is really easy if you have an HDMI monitor, keyboard, and mouse.

Subsequently getting an SSH connection to your pi is easy if you have a home router with internet access that you’re both (your PC and your pi) connected to.

But let’s say you’re on an airplane and you pull your Raspberry Pi out of its box and you want to get set up. We call that provisioning. How would you do that?

I’ll propose my method.

First, you need to plug your pi into your PC using an ethernet cable. If you’re a technologist of old like I am, you may be rummaging through your stash for a crossover cable at this point. It turns out that’s not necessary though. I was pretty interested to discover that modern networking hardware has auto-detection that is able to determine that you have a network adapter plugged directly into another network adapter and crosses it over for you. This means I only have to carry one ethernet cable in my go bag. Nice.

If you put a new OS image on your pi and boot it up, it already detects and supports the ethernet NIC, so it should get connected and get an IP automatically.

Here comes the seemingly difficult part. How do you determine what the IP address of your pi is if you don’t have a screen?

The great thing is that the pi will tell you if you know how to listen.

The means by which you listen is called mDNS. mDNS (Multicast DNS) resolves host names to IP addresses within small networks that do not have a local name server. You may also hear mDNS called zero configuration and Apple implemented it and felt compelled (as they tend to) to rename it - they call it Bonjour.

This service is included by default on the Raspberry Pi’s base build of Raspbian, and what it means is that out of the box, the pi is broadcasting its IP address.

To access it, however, you also need mDNS installed on your system. The easiest way I am aware of to do this is to download and install Apple’s Bonjour Print Services for Windows. I’m not certain, but I believe if you have a Mac this service is already there.

Once you have mDNS capability, you simply…

ping raspberrypi.local -4

The name raspberrypi is there because that’s the default hostname of a Raspberry Pi. I like to change the hostname of my devices so I can distinguish one from another, but out of the box, your pi will be called raspberrypi. The .local is there because that’s the way mDNS works. And finally, the -4 is an argument that specifically requests the IPv4 address.

If everything works as expected you’ll see something like…

Again, my pi has been renamed to cfpi1, but yours should be called raspberrypi if it’s new.

My system uses 192.168.1.X addresses for my wireless adapter and 169.254.X.X for my ethernet adapter.

So that’s the information I needed. I can now SSH to the device using…

ssh pi@169.254.187.84

I could just use ssh pi@raspberrypi.local to remote to it, but I’ve found that continuing to force this local name resolution comes with a little time cost, so it’s sometimes significantly faster to hit the IP address directly. I only use the mDNS to discover the IP and then I use the IP after that.

Provisioning a Raspberry Pi usually includes a number of system configuration steps too. You need to connect it to wireless, set the locale and keyboard language, and maybe turn on services like the camera. If you’re used to doing this through the Raspbian Configuration in XWindows, fear not. You can also do this from the command line using…

sudo raspi-configuration

Most everything you need is in there.

You may also be wanting to tell your pi about your wifi router so it’s able to connect to via wireless the next time you boot up. For that, check out my post at codefoster.com/pi-wifi. Actually, if you’re playing a lot with the Raspberry Pi, you might want to visit codefoster.com/pi and see all of the posts I’ve written on the device.

Happy hacking!

I beat my head against a wall for a long time wondering why I wasn’t able to do basic GPIO on a Raspberry Pi using Node. Even after a fresh image and install, I was getting cryptic node error messages when I ran my basic blinky app.

Lucky for me (and perhaps you) I got to the bottom of it and am going to document it here for posterity. Let’s go.

The head beating happened at a hackathon I recently attended with some colleagues.

The task was simple - turn on an LED. It’s so simple that it’s become the “hello world” app of the IoT world. There’s zero reason in the world why this task should take more than 10 minutes. And yet I was stumped.

After a fresh image of Raspbian, an install of NVM, and then a subsequent installation of Node.js 6.2.2, I wrote a blink app using a variety of modules. I used pi-gpio, rpi-gpio, onoff, and finally johnny-five and the raspi-io driver.

None of these strategies were successful. Ugh. Node worked fine, but any of the libraries that accessed the GPIO were failing.

I was getting an obscure error about an undefined symbol: node_module_register. No amount of searching was bringing me any help until I found this GitHub issue where nodesocket (thanks, nodesocket!) mentioned that he had the same issue and it was caused by an NVM install of Node and an accidental, residual version of node still living in /usr/local/bin. In fact, that was exactly what was happening for me. It was a subtle issue. Running node -v returned my v6.2.2. Running which node returned my NVM version. But somewhere in the build process of the GPIO modules, the old version (v0.10) of node from the /usr/local/bin folder was being used.

There are two resolutions to this problem. You can kill the old version of node by deleting the linked file using sudo rm /usr/local/bin/node and then create a new one pointing to your NVM node. I decided, however, to deactive NVM…

nvm deactivate

…and then follow these instructions (from here) to install a single version node…

wget http://nodejs.org/dist/v6.2.2/node-v6.2.2-linux-armv7l.tar.xz`` # Copied link
tar -xf node-v6.2.2-linux-armv7l.tar.xz # Name of the file that was downloaded
sudo mv node-v6.2.2-linux-armv7l /usr/local/node
cd /usr/local/bin
sudo ln -s /usr/local/node/bin/node node
sudo ln -s /usr/local/node/bin/npm npm

I like using NVM on my dev machine, but it’s logical and simpler to use a single, static version of Node on the pi itself.

EDIT (2016-12-14): Since writing this, I discovered the awesomeness of nvs. Check it out for yourself.

And that did it. I had blinky working in under 3 minutes and considering I get quite obsessive about unresolved issues like this, I had a massive weight lifted.

BTW, through this process I also learned about how the GPIO works at the lowest level on the pi, and I blogged about that at codefoster.com/pi-basicgpio.

I’ve been doing a lot of hacking on the Raspberry Pi, and I’ve written a few articles on the topic. I’ve assembled all of my posts here for easy access.

• Accidental Old Version of Node on the Raspberry Pi - I beat my head against a wall for a long time wondering why I wasn’t able to do basic GPIO on a Raspberry Pi using Node. Even after a fresh image and install, I was getting cryptic node error messages when I ran my basic blinky app.Lucky for me (and perhaps you) I got to the bottom of it and am going to document it here for posterity.
• The Most Basic Way to Access GPIO on a Raspberry Pi - I’m always looking for the lowest level understanding, because I hate not knowing how things work. On a Raspberry Pi, I’m able to write a Node app that changes GPIO, but how does that work? Turns out it’s pretty interesting. I’ll show you.
• Easy and Offline Connection to your Raspberry Pi - Getting a Raspberry Pi online is really easy if you have an HDMI monitor, keyboard, and mouse, but what about if you want to get connected to your Pi while you’re, say, flying on a plane?
• Wifi on the Command Line on a Raspberry Pi - How to configure wireless connections on your Raspberry Pi from the command line.