Building MonoDevelop for the PINE64

MonoDevelop running on the PINE64 using SSH X11 forwarding

4 Dec 2017 Update
These instructions will not work with the latest versions of Mono and MonoDevelop from github. I tried compiling from scratch on a new image, and they will work with the following versions listed below. You can checkout the specific tags immediately after cloning the corresponding repositories before you start building.
Mono 4.8.1.0 – git checkout tags/mono-4.8.1.0
MonoDevelop 6.1.0.5441 – git checkout tags/monodevelop-6.1.0.5441

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.

Some reference PCL Assemblies are required for the build to complete. You will need to build a deb package and install following the instructions below.

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

 

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

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.