Controlling an Arduino connected to the PINE64 over I2C with C and C#

In a previous post, we connected an Arduino Mega to the PINE64 and wrote a sketch for the Mega for data communication. The data to be sent and received will follow the simple rules which were listed in the post. Next, we’re going to write a shared library with some C code to interface with I2C natively, and then a C# class which will call the shared library and bring everything together. Just a quick recap of the data rules:

  • Maximum length: 16 bytes.
  • First byte: Number of bytes sent/received.
  • Second byte: Control command. CMD_DIGITAL_WRITE (0x01 or 1), CMD_DIGITAL_READ (0x02 or 2) and CMD_ANALOG_WRITE (0x03 or 3).
  • Third byte: Pin number.
  • Fourth byte: Value of either 1 (for high) or 0 (for low) for CMD_DIGITAL_WRITE, or
  • Fourth to seventh bytes: Integer value for CMD_ANALOG_WRITE.

Linux has native I2C support which lets us communicate directly with any device connected to the bus. Since native communication is possible, we create a shared library with methods which can be invoked from our C# code. Since we can open the connection to a device on the I2C bus as a file descriptor, we will be making use of fcntl.h for the descriptor. Let’s take a look at the C library.

The first thing we do is include required headers and define a constant specifying the maximum number of bytes, which is 16. Then we create the nanite_i2c_open function try to open the specified device file (usually /dev/i2c-1). Next we call ioctl so that we will be able to control the device using a reference to the file descriptor, and the specified slave address. The file descriptor is returned for reference in other function calls. If any of the steps in the function fails, -1 is returned to indicate an error condition. Other functions in the library will handle the failure the same way.

The nanite_i2c_close function is fairly simple. It takes the file descriptor as an argument and checks if it is open in order to close it.

Next is the nanite_i2c_send function which takes the file descriptor and the data to be sent as arguments. The bytes are written to the open file descriptor, and the number of bytes written is verified. If it does not match the length defined in the first byte, -1 is returned to indicate an error condition.

The nanite_i2c_read function will be used to read data over I2C. The first byte is retrieved in order to determine how many more bytes to read. Then we validate the number of bytes that were received with the expected length. 0 is returned if the operation was successful.

The final function in the library is nanite_i2c_max_bytes() which returns MAX_BYTES. This gives us a complete library that we can use for I2C data communication. You can create the shared library using gcc -shared -o libnanitei2c.so -fPIC main.c. The full code listing for the library is available at https://gitlab.com/akinwale/nanitei2c/blob/master/main.c.

Using DllImport, we can call functions from the shared library in the C# code which we’re going to look at next. We create our class, define the supported commands as an enumeration and specify the private members. We also define a couple of constructors with the default constructor using the default I2C device file which is /dev/i2c-1 on the PINE.

The DllImport calls are defined within the class and are used to map the functions from the library to functions that we can call in the I2CExtendedIO class. For instance, to call the nanite_i2c_send in the class, we’ll make use of I2CSendBytes.

Here, we’ve defined our class dispose function which closes the file descriptor if it is open. We also have a bunch of simple helper functions which will be called within the class.

The Open function is simple as it delegates to the OpenI2C function with the specified device filename and the slave address, and assigns the returned file descriptor to a private member.

With DigitalWrite, we build the data to be sent based on the specified rules. Then we delegate to I2CSendBytes using the specified arguments, which calls the corresponding library function.

AnalogWrite is similar to DigitalWrite, except that we convert the integer value to 4 bytes instead of the single byte for low (0) or high (1). Valid values are between 0 and 255 inclusive.

To wrap it all up, we have the DigitalRead function which is a little different because we have to send data and then immediately receive a response. We obtain a mutual-exclusion lock so that the send and receive process completes before any subsequent operations are run. Then we validate the received data and return the value for the pin that was read.

You can obtain the full code listing for the C# class at https://gitlab.com/akinwale/NaniteIo/blob/master/Nanite/IO/I2CExtendedIO.cs.

We can put this all together and test with a simple interactive console application.

The console application accepts inputs like 13 on, 18 off or 9 analog 172 which makes it easy to test the Arduino pins. Although this is practically a complete solution for most requirements with respect to controlling an Arduino connected to the PINE (or Pi or any other SBC) over I2C using C#, you could choose to implement an additional command for analogRead. All you would have to do is follow the logic for digitalRead and add the necessary code to the sketch and the C# class.

Extending GPIO with an Arduino connected to the PINE64 using I2C

Although the PINE64 provides quite a decent number of GPIO pins, there are several reasons that you may want to have access to more pins. For example, the Arduino can provide an extra number of native PWM pins, or you may want to implement low-level control of a robot using the Arduino, with high-level operations being handled by the PINE. This post will cover how this can be achieved with the PINE64 and an Arduino Mega. We’ll also create a sketch for the Mega which for handling I2C communication. In the next post, we will write some C and C# code which will show how to send and receive data between the PINE and the Mega. Note that this can be done with any single board computer that supports I2C including any of the Raspberry Pis, the Beagleboard and others.

PINE64 connected to Arduino Mega over I2C

I2C stands for Inter-Integrated Circuit and it is a serial computer bus that enables communication between multiple devices that support the protocol. Every board that supports I2C will have 2 pins called SDA (serial data line) and SCL (serial clock line).

Pins 3 and 5 of the Pi 2 pinout on the PINE64 are the SDA and SCL pins respectively. On the Mega, they are pins 20 and 21. Connect the SDA and SCL pins from the PINE64 to the SDA and SCL pins respectively on the Arduino. I have also connected the 5V from the PINE to the Mega in order for the Mega to be powered by the PINE. If you decide to take this approach, one of the ground pins also has to be connected between both boards.

A closer look at the I2C connection between the PINE64 and the Arduino Mega

Before connecting the Mega, we’ll need to create and upload a sketch that will assign an I2C address which will be used to access the device. The sketch will make use of the Wire library which will be used for I2C communication. We will be making use of byte arrays to send and receive data over the I2C bus. You can come up with a fancy protocol for this, but I came up with the following simple rules.

  • Maximum length of 16 bytes.
  • First byte will always be the length (inclusive of the first byte) of the data sent or received.
  • Second byte is the command. We’ll support 3 simple commands, digital write (0x01 or 1), digital read (0x02 or 2) and analog write (0x03 or 3).
  • Third byte is the pin number.
  • For digital write only, fourth byte be a value of either 1 (for high) or 0 (for low).
  • For analog write only, the next four bytes after the third byte will store an integer value between 0 and 255 inclusive.

With that out of the way, let’s take a look at the sketch. First things first, define our constants and variables.

The code is straightforward. We define 0x08 as the I2C address that we want the Mega to use. We also define our commands, pin states (for digital read / write), buffers for storing data to be sent and received and other variables that will be used. The ioPins array is a list of all the pins available on the Mega. This will need to be changed to match the board that the sketch will be uploaded to. The ioPinStates is a pseudo hashmap which will map the pin number (used as the array index) to one of the defined pin states (IO_PIN_STATE_INPUT or IO_PIN_STATE_OUTPUT). We’re keeping track of the pin states so that we can activate the pins on demand, instead of activating them all at once in the setup() function.

The setup function simply initialises the Wire library using the specified I2C address, and enables Serial output which will be used to output debug messages. Wire.onReceive registers the onDataReceived function which will be called when data is sent from the PINE64, while Wire.onRequest registers the onDataRequested function which will be called when the PINE64 requests data from the Mega. The isPinValid function is a helper method which checks if the pin specified as the parameter is valid for the board. It checks the pin against the ioPins array that we defined earlier.

Next is the onDataReceived function which handles most of the work. It accepts an argument which represents the number of bytes that were received.

The while loop checks if there is data available from the Wire library. If there is, the absolute minimum number of bytes received that can be considered valid based on the rules we defined earlier is 3 (length, command, pin). If the number of bytes received is less than 3, then the function ends at that point and output is written to the Serial console. The next step is to use a switch statement to check and handle the command that was received. The second byte (index 1) contains this data.

For digital write, the minimum number of bytes to be considered valid is 4 (length, command, pin, value). The function is terminated if we received less than 4 bytes for the command. The isPinValid is called to check if the pin received is valid, and if it isn’t, the function ends at that point. Next thing to be done is to check if the pin has been activated. We make use of the ioPinStates array to do this making use of the pin number as the index. If the pin has not yet been activated (IO_PIN_STATE_OUTPUT), then we activate the pin using pinMode. Once this check is complete, we can call digitalWrite using the pin and the value specified.

Digital read also follows the same set of steps as digital write (validate date length, validate pin, check pin state) but we will call the actual digitalRead function in onDataRequested. What we do here is store the command and the pin in variables (lastReadCommand and lastReadPin respectively) which we can then make use of in onDataRequested.

Similar to digital write, analog write follows a couple of steps (validate data length and validate pin). We don’t need to check or set the pin state before calling the analogWrite function. We check that the value is between 0 and 255 inclusive before calling analogWrite with the pin and the value as the arguments.

If the data sent did not match any of the defined commands, the code falls back to the default statement which outputs Unrecognised command. to the serial command, and then the onDataReceived function will be called again when new data is received.

Finally, we have the onDataRequested function which makes use of lastReadCommand and lastReadPin. The function is straightforward, as it uses the Wire library to send data back to the PINE following our simple rules.

And that’s it! Compile the sketch using the Arduino IDE and then upload it to your board. Connect your Arduino to the PINE after the sketch is successfully uploaded, and boot up the PINE. You can obtain the full code listing for the sketch at https://gitlab.com/akinwale/nanitei2c/blob/master/nanitei2c_mega.ino.

Install i2c-tools using sudo apt-get install i2c-tools. By default, only root can use the I2C commands, but you can add the user account with useradd -G i2c ubuntu (replace ubuntu with the username that you want to use to access I2C). Reboot the PINE and then scan the I2C bus with the using i2cdetect -y 1. You should get output should be similar to the following:

Based on this output, we can see that the Mega was recognised over the I2C bus with the configured address in our sketch (0x08 or 8). With this, we have access to the extra pins which we will be able to control directly from the PINE. That’s pretty neat. In the next post, we will write the C and C# code for the PINE for handling I2C communication.

Control GPIO pins on the PINE64 with C#

Similar to the Raspberry Pi, GPIO pins on the PINE64 can be controlled through sysfs. You can refer to my previous post which goes into the concept in detail, and the C# code remains the same for the PINE64. However, with the longsleep Ubuntu image, root access is required to control the GPIO pins. You will need to grant the necessary permissions in order to be able to control GPIO pins as a normal user.

Granting user permissions
We’ll assume that we want to be able to control the pins as the default ubuntu user. Follow these steps to grant the necessary permissions.

  1. Create a user group called gpio.
    groupadd gpio
  2. Add the ubuntu user to the gpio group.
    useradd -G gpio ubuntu
  3. Add a udev rule to run chown on the sysfs files. The chown command will set group ownership to the gpio group. Adding the udev rule will run the chown command automatically whenever you export a pin. Create a file called 99-com.rules in /etc/dev/rules.d and paste the following contents.

    Physical pin to GPIO number mapping
    I took some time to test the physical pins on the PINE in order to determine the sysfs gpio numbers and came up with this table. As an example, physical pin 22 on the Pi 2 pinout corresponds to /sys/class/gpio/gpio79.

    Pin #GPIO #
    Pi 2 pinout
    3227
    5226
    832
    1033
    1171
    1272
    13233
    1576
    1677
    1878
    1964
    2165
    2279
    2366
    2467
    26231
    27361
    28360
    29229
    31230
    3268
    3369
    3573
    3670
    3780
    3874
    4075
    Euler pinout
    7363
    10232
    1135
    1236
    1337
    1538
    1639
    18100
    1998
    2199
    22101
    2397
    2496
    26102
    2734
    28103
    2940
    3041
    Exp pinout
    2359
    740
    841

Measuring PINE64 Idle Power Consumption

I got a DROK digital multimeter and I decided to find out just how much power the PINE64 consumes running headless.

PINE64 connected to RAVPOWER powerbank through DROK multimeter

The measurements were taken on my 1GB PINE64 running longsleep’s Ubuntu image. The measured voltage from the powerbank is 5.06V.

 CPU @ 1152MHzCPU @ 480MHz
WiFi / BT module plugged in260mA (1.32W)200mA (1.01W)
WiFi / BT module removed250mA (1.27W)190mA (0.96W)

This is not by any means a proper scientific test, but it gives an idea of what to expect. Got any tips for reducing power consumption? Feel free to share them in the comments below.

Building MonoDevelop for the PINE64

My PINE64 is here and the first thing I decided to do was build MonoDevelop which I’ll use to manage C# projects, since most of the code I’ll be writing for my autonomous project will be in C#. I’m using the longsleep Ubuntu Xenial image as a base, so these instructions assume that this is what you have installed. You can adapt as required based on your distro.

Of course, the easiest way to get MonoDevelop installed is by using the package manager. The version is also fairly recent (4.2.1.102), so you can choose skip the rest of this post if you prefer. Simply run the apt-get install command and all required dependencies will also be automatically installed.

Most of the steps will be similar to the MonoDevelop for Raspberry Pi build post, but we’ll be skipping fsharp altogether. I cloned the fsharp repository but the make process failed due to the following error:

F# is only required for the fsharpbindings extension and I don’t plan on using that. There appears to be an fsharp package which you can install using apt, but this will also install the mono 4.2.1 dependencies. If you’re fine with using an older version of mono and would still like to build MonoDevelop, then you can also skip the steps up till Build MonoDevelop.

So let’s get started!

Install all prerequisites
Git is required to clone the source repositories for Mono, MonoDevelop and dependencies. The other packages are required for building MonoDevelop dependencies from source.

 

Pre-build: NuGet certificates
The MonoDevelop build process makes use of NuGet at certain points. You will need to import certificates into your certificate store using the following commands.

 

Build Mono
This step is fairly straightforward. Clone the mono source repository and run the build process.

This build will take a while. If you wish to run the mono and mcs test suites, you can do a make check before make install.

Build MonoDevelop dependencies
MonoDevelop requires gtk-sharp and gnome-sharp to be installed on the system. To build gtk-sharp.

gnome-sharp follows a similar process.

 

Build MonoDevelop
First, we clone the monodevelop repository and initialise the submodules using git.

Next, we remove references to fsharp. The assumed working directory for these steps is the top-level monodevelop source directory.

Remove the external/fsharpbinding/MonoDevelop.FSharpBinding/FSharpBinding.addin.xml \ line, save the file and close.

Comment out or remove the following lines in the file and save your changes. To comment out the lines, simply prefix each line with the # character.

Then we can go on to build the IDE.

You can run mono main/.nuget/NuGet.exe update -self if you get the following error after running make.

Once the build is successfully completed, you can run the application using monodevelop. If you have X11 forwarding enabled for your SSH session, you should see the MonoDevelop IDE on your screen after a couple of seconds.

MonoDevelop running on the PINE64 using SSH X11 forwarding
MonoDevelop running on the PINE64 using SSH X11 forwarding

The PINE64 is finally here

I received my PINE64 yesterday and I was pretty excited after such a long wait. The following items were in the package:

  • PINE64 1GB board
  • Camera module
  • RTC battery module (which is actually bigger than I expected)
  • WiFi/Bluetooth module

They were all in good shape, and the board was not bent nor warped which I was afraid would happen after reading a few horror stories. The Pine64 is most definitely a huge board (compared to the Raspberry Pi), and the build quality also seems solid. I was able to burn the longsleep Ubuntu Xenial image to a 32GB microSD card, and since I wanted to run the board as a headless device, I mounted the microSD on my Linux box and updated the /etc/network/interfaces file to connect to my wireless network. The connection to the network was established a few seconds after providing power to the board and I was able to SSH into the device after the boot process was successfully completed.

I’ll update this post with a few pictures once I get a decent camera.

Update

1GB PINE64 with the WiFi module and RTC battery module installed. It's huge!
1GB PINE64 with the WiFi module and RTC battery module installed. It’s huge!
PINE64 side-by-side with a Raspberry Pi 3 and the Keyestudio Mega clone
PINE64 side-by-side with a Raspberry Pi 3 and the Keyestudio Mega clone

Building Visual Studio Code for the Raspberry Pi 3

If you’d rather prefer to use Visual Studio Code for C# development instead of MonoDevelop, you can build Microsoft’s own Visual Studio Code from the source repository. I’ve used Visual Studio Code on Ubuntu and it’s actually a pretty neat tool for developing on Linux. It supports over 30 languages including C#, C++, Python, Java and more, so even if you’re not writing C# code, it’s still a useful tool.

Prerequisites for the build on Linux include Python 2.7, make and libx11-dev which should already be installed on your Pi if you started of with a Raspbian Jessie image. Also, if git has not been installed yet, run sudo apt-get install git. Nodejs and npm also need to be installed, as they will be used by the build script to retrieve some required packages. A recent version of nodejs has to be downloaded since the package version in the repository is not adequate.

Install required dependencies for running Visual Studio Code.

Let’s clone the repository and start the build process.

If you get an error like so:

edit npm-shrinkwrap.json and delete the following lines.

Once the build is completed, you can run:

The script will download a few more required files and perform a few initialisation steps before the IDE launches. The editor performance was very poor when I ran it using X11 forwarding however. Perhaps, it works better if running within a native X11 display.

Visual Studio Code running on the Raspberry Pi 3 using X11 forwarding
Visual Studio Code running on the Raspberry Pi 3 using X11 forwarding

How to control GPIO pins on the Raspberry Pi 3 using C#

GPIO pins on the Raspberry Pi can be controlled using the sysfs interface, which is a virtual filesystem that the Linux kernel provides. In this guide, we will write a basic C# class to control available pins on the Pi through sysfs.

Understanding the sysfs interface
sysfs provides access to the GPIO pins at the path /sys/class/gpio. You can cd into this path and ls to list files in the directory. There are two special files here which are export and unexport. You write to the export file to activate a particular pin, while writing to unexport deactivates the pin. The following example activates GPIO pin 18.

You can verify that the pin is activated by listing the files in the /sys/class/gpio directory. You should see a gpio18 folder in the directory listing. After the pin has been activated, you should specify whether the pin should be an input or output pin before you can read or write values. You do this for input like so:

Or for output:

If the pin is specified as an output pin, you can write a value of either 0 (low) or 1 (high) for the pin. If a LED is connected to the pin for this example, a value of 0 will turn the LED off, while a value of 1 will turn the LED on. To specify the pin value, you can do this:

Once you are done with the pin, you can deactivate it using:

Writing the C# class
Now that we have an idea of how sysfs works, we can create a class to implement the necessary steps. The sysfs approach basically requires writing values to the file, so we can use simple file I/O operations to achieve the desired result. The full listing for the GPIO class can be found at https://gitlab.com/akinwale/NaniteIo/blob/master/Nanite/IO/GPIO.cs.

The first thing we’ll do is add the using statements for the namespaces. System.IO is required for FileStream, StreamReader and StreamWriter which are used for file I/O. System.Threading is required for the Thread class, while Nanite.Exceptions contains the custom exceptions defined for our project. We’ll also define enumerations for the GPIO direction and value, and a few constants for strings like the GPIO path and other special files. The class will be defined as static, because we do not need to create an instance of the class.

Pretty straightforward so far. The first method we’re going to define is the PinMode method, which will take the pin number and direction as parameters. This method will activate the pin and then set the direction to either in or out depending on the specified parameter value.

We build the pinPath string making use of Path.Combine(GPIOPath, string.Format("gpio{0}", pin));. If the value specified for the pin parameter is 18, pinPath will contain the string, "/sys/class/gpio/gpio18". The ClosePin method call is optional, but the idea behind this is that the pin should be deactivated first before activating. We also check if the gpio pin directory exists using if (!Directory.Exists(pinPath)) before activating to make sure we are not activating a pin that has already been activated.

After the request for pin activation, there may be a small delay which is why we have a while loop which waits until the corresponding gpio pin directory has been created before we set the pin direction. Thread.Sleep(500) makes the program wait 500 milliseconds before proceeding to the next statement. Note that this while loop is completely optional, but it acts as a safeguard against setting the pin direction before the gpio pin directory has been created by the system. One thing to take note of is if the gpio pin directory never gets created (for instance, if the pin is invalid), the loop may end up running forever. To fix this, we can set a maximum number of times the loop should run before ending the loop.

The next method is the ClosePin method which takes the pin number as a parameter. This method checks if the pin directory exists before it writes the pin number to the /sys/class/gpio/unexport file.

We create the Write method to write a value to a pin. It takes two parameters, the pin number and the value which is of the Value enumerator type with possible values Value.Low or Value.High. In this method, we make use Path.Combine to create the full path to the value file in the gpio pin directory. For pin 18, this will be "/sys/class/gpio/gpio18/value". If value for the value parameter is Value.Low, we write 0 to the file, otherwise if it’s Value.High, we write 1 to the file.

Finally, we have our Read method to read a value from a pin. It will return either Value.Low or Value.High depending on what the pin has been set to. The question mark at the end of the method return type indicates that we can return null for the method if the value retrieved is invalid.

To determine if the retrieved value is valid, we add a couple of checks in the method. The first is the int.TryParse method, which returns false if the retrieved value is not a valid integer. Then verify that the value is either 0 or 1 using if (pinValue != 0 && pinValue != 1). If it’s neither 0 nor 1, null is returned. Otherwise, the corresponding enumeration value is returned by casting the integer to GPIO.Value.

Finally, we can put this all together in a sample program. If a LED is connected to pin 18, the LED will light up when the value is set to High and turn off when the value is set to Low.

Source Code
The full code listing for the GPIO class can be obtained from https://gitlab.com/akinwale/NaniteIo/blob/master/Nanite/IO/GPIO.cs.

Building MonoDevelop for the Raspberry Pi 3

Since I will be using C# for most of my development (with a combination of C for some native system functionality), I decided to go with Mono. This guide is based on the assumption that you’re running the May 2016 Raspbian Jessie Lite image. The easiest way to get MonoDevelop up and running would be to run sudo apt-get install monodevelop which would also handle all the necessary dependencies including the Mono runtime. However, the versions in the repository are pretty old, and I want to be able to make use of .NET 4 features.

Another option for .NET development on Linux is .NET Core. Version 1.0 was officially announced by Microsoft a few days ago, but there aren’t ARM binaries available and I haven’t been able to successfully build it for the Pi, yet.

Git
The Mono project code is hosted on Github, so the first thing to be done is to install git.

Build Mono
Obtain the source code from the Github repository using the command

Then install the Mono build process prerequisites.

You can follow the build instructions in the README.md for the repository at https://github.com/mono/mono/blob/master/README.md. To summarise, change to the source root directory (cd mono) and run the following commands.

If you wish to run the mono and mcs test suites, you can do a make check before make install. The build will take quite a while, so you have to be patient. I didn’t time my build, but my best guess would be about 3 to 4 hours.

Build FSharp
MonoDevelop apparently requires the F# compiler to be installed. First thing to do is to import trusted root certificates required by the NuGet package manager into the machine store. The NuGet package manager retrieves certain required packages as part of the build process, so this is required.

Next, we clone the FSharp git repository and build.

Build additional MonoDevelop dependencies
MonoDevelop also requires gtk-sharp and gnome-sharp to be installed on the system. The first step is to install the rest of the apt dependencies for all three packages.

devscripts will be used to create a package of PCL Assemblies which is required for the MonoDevelop build process.

Once the dependencies have been installed, gtk-sharp should be built first and then gnome-sharp.

To build gtk-sharp

And gnome-sharp

Build MonoDevelop
If you made it through all of that, you can finally proceed to build MonoDevelop. But there are a few caveats which we’ll cover in a bit.

The first error I encountered after I running make was an issue with NuGet not finding a number of packages. To fix this while your current directory is the monodevelop directory, run the following commands and then run make again (if you’ve run it previously).

The next error stated that certain PCL Assemblies were missing. To sort this out

Remove mono-xbuild from the list of dependencies in the control file, save and close. Then continue with the following commands.

The final error had to do with the fsharpbinding regarding missing references in a particular assembly. Since I don’t need the F# bindings, and it’s not a required feature, I removed it from the build process using the following steps (assuming the monodevelop source directory is the working directory).

Remove the external/fsharpbinding/MonoDevelop.FSharpBinding/FSharpBinding.addin.xml \ line, save the file and close.

Finally, you can build and install.

This build will also take a bit of time, so sit back, relax and rest easy. Once the installation is complete, you can simply run it by typing monodevelop at the command line (assuming you have X11 forwarding enabled in your SSH session).

Getting started with the Raspberry Pi 3

It’s taken quite a while for my PINE64 to arrive. Apparently, the shipping was delayed because the addon camera module was not ready yet. Quite disappointing, but I guess it’s to be expected since it’s a Kickstarter project. In the mean time, I decided to grab a Raspberry Pi 3 so that I could start off with my autonomous robot project.

I started off with the Raspbian Jessie Lite image which is a 292MB download (May 2016 version). Got it set up on a Sandisk 32GB microSD card and booted it up. I was planning to connect to it using a USB to TTL serial cable as I don’t have any USB peripherals available, nor an Ethernet cable. The plan was to configure the wireless connection so that I could SSH into it (and use X forwarding for GUI applications) once it booted. This did not go smoothly, and it took quite some time to figure out since a lot of the information online only applies to the earlier Pi models.

It turns out the default Raspbian image for the Pi 3 does not support serial connections out of the box due to the in-built Bluetooth module, so I had to make some adjustments to get this to work. Hence, this is sort of a beginner’s mini guide to working with a headless Raspberry Pi 3. The following instructions will require a Linux box.

So how do you get Pi 3 serial to work?
Note that these instructions are based on the May 2016 Raspbian Jessie Lite image. I mounted the SD card on my laptop’s Ubuntu installation, and had to chroot into it (following instructions at https://hblok.net/blog/posts/2014/02/06/chroot-to-arm/) to run a few updates. Inserting the SD card will create 2 mount points: the /mnt/boot/ partition and the main partition which we’ll refer to as /mnt/main/ (note that the path to the mount points may be different depending on your Linux distribution, so verify). After mounting, run the following commands.

Before you can chroot, you need to be able to run ARM binaries using qemu.

Next, register the ARM executable format with the QEMU static binary.

Now, you can chroot into /mnt/main

If you get an error stating that ‘/bin/bash’ was not found, you may have to run

Once you’ve chrooted in, update the system.

If you get an error along the lines of qemu: uncaught target signal 4 (Illegal instruction) - core dumped, edit /etc/ld.so.preload and comment out the lines in the file.

Next, you’ll need to install and run rpi-update.

Once the update is completed, edit the /boot/config.txt file. Add these lines to the end of the file and save.

Unmount the microSD card and insert it into your Pi. Connect the appropriate pins for your Pi using your USB-to-TTL serial cable and plug it into your host. Instructions for this can be found at http://workshop.raspberrypiaustralia.com/usb/ttl/connecting/2014/08/31/01-connecting-to-raspberry-pi-via-usb/. Note that if you’re going to use an external power source, you do not need to connect the 5V pin from the serial cable. Connecting to the 5V pin while an external power source is connected may damage your Pi, so be careful!

You should then be able to access your Pi using screen (or your preferred serial client). Note that /dev/ttyUSB0 is the port attached after the cable was connected. To find out what port your USB cable is attached to, you can run dmesg | tail after you connect the cable.

If you see a blank screen, your Pi has probably already finished booting up, so just type your login username and press Enter. Alternatively, you can reboot your Pi (without disconnecting the USB cable from your host) and then you should be able to see the boot messages in the serial console before the login prompt is displayed.

Configure Pi 3 WiFi from the command line
After you’re logged in, you’ll need to configure your WLAN connection. Just edit /etc/wpa_supplicant/wpa_supplicant.conf and add the following lines replacing [networkssid] and [key] with the WiFi SSID and the access key respectively:

Save the file and then run the following commands

Next, check if the connection was successfully established. If you see inet addr after running the ifconfig command, then you’re connected to the network and you can SSH in (after raspi-config) from a different device on the network.

Enable I2C and SSH with raspi-config
With raspi-config, you can make a number of configuration changes to your Pi 3. Enabling SSH is required for remote access and I plan to use I2C to connect to an Arduino Mega in order to control the pins, so I2C has to be enabled as well. To enable both, launch raspi-config.

Then select Advanced Options, and then enable the SSH and I2C options. You can also explore the other configuration settings and modify them to suit your needs.

What now?
That’s it! I will be writing about the software I’m installing on the Pi 3 relating to my autonomous robot project over the next few posts. I will also create posts related to the PINE64 once I have the board in my hands. Hopefully, very soon!