If you have “broken the ice” with GNU / Linux through Raspberry Pi already, here is a board that allows you to jump into the real professional world, with all the needed support and with totally “Open” instruments and, why not, in an enjoyable way. Arietta G25 is the “mascot” of a series of professional boards designed and made in Italy by Acme Systems. That also provides support to its boards for the next 5 years.

Arietta G25 condenses into a few low-cost square inches many years of experience in embedded GNU / Linux, concretized in the manufacturing of professional systems currently distributed over thousands of units.

The technical features we will describe below are definitely innovative for a board of this size. Besides, the technical level of the board design and the software approach is so high that assigns to Arietta an important role in the professional use of embedded GNU / Linux, allowing customizing and optimizing the GNU / Linux kernel on our project requirements.

“Factotum” Kernel such as Raspberry Pi, full of plug and play drivers and modules simplifies the management for most peripherals, but generates a heavy distribution, both in terms of memory usage and performance. In our case, we can keep the kernel as “lean” as possible, saving memory and CPU cycles while maintaining respectable performance. This also for the benefit of a limited energy consumption, making it possible to use a battery to feed the whole board.

The board is equipped with a 40-pin configurable GPIO I/O. In addition to the standard digital I/O, there are several pins that can be configured either as generic digital I/O or as analog ADC and PWM inputs/outputs, as well as I2C, SPI, I2S and UART. The engineers of ACME Systems wanted to add value to their offering with a website full of information and tutorials for users of their boards. In particular, there is an application to configure the different pins and automatically generate the file .dtb (Device Tree Blob) used to bind the desired functions to the corresponding physical pin. The .dtb file is read by the kernel at boot time for the initial system configuration, associating the SoC pins of the physical GPIO pins, and loads their drivers.

There are instructions on the website on how to recompile the kernel to include specific drivers, but also to use precompiled images directly.

Arietta G25 Features

We can see the layout of the board with the indication of the connectors and the main and additional components.

Let us see the main features:

Consequently, the functions described below are not all available at the same time:

Let us prepare the Arietta G25 board

For the first use, we recommend to use the board with his WiFi adapter and the FTDI converter to access to the console. Those two tiny devices can be soldered directly on the board or mounted on a 7mm female stripe, 2mm spacing for the WiFi and on a 6mm male, 2,54mm spacing for the serial interface.

We have chosen the WiFi adapter with the external antenna connector. We assemble the pigtail cable and the antenna on the module, and then we plug both modules on their connectors. If we do not think of using any GPIO pin, the board is ready. Now we need to power the board and connect to it for the customizations.

In this case there are several possibilities. You can connect via “serial console”, or connect via micro USB “Device Port”, in which case the board is “seen” as a LAN adapter. We can connect to WiFi using the extension module that we mentioned or finally using a wired Ethernet cabling to GPIO a USB port and using a LAN adapter / USB.

For a first “exploratory” use we still have several possibilities. To begin, let us connect the mini USB cable to DPI serial module. Open a PuTTY terminal on our PC and configure it as shown.

We configure the field “Connection type” to “Serial”. In Serial line, insert the COM port number assigned to the DPI converter. We set “Speed” to “115200”.

This opens the serial communication, currently inactive. Let’s take a couple of returns and we will see red LED flashing on the DPI module. Now connect the Micro USB cable to the micro USB connector “Device Port” and the other side to another USB port on the PC. Arietta G25 will start on boot, and we can see the messages in console.

Meanwhile, being the first time that we connect Arietta G25 via USB, the RNDIS / Ethernet Gadget drivers will be installed for the adapter. If you use a PC with XP or however the driver is not retrieved automatically, you can download it from address

http://www.driverscape.com/download/rndis-ethernet-gadget

Choose the correct version for your system. Unzip in a folder specially created and run the driver update pointing to the newly created folder. At the end, if you go to Settings >> Network Connections, you’ll see a new LAN connection. Click with the right mouse button on the new tab and select “Properties” from the drop down menu. Here you set the adapter’s IP address and subnet mask with the following values:

IP 192.168.10.20

Subnet Mask: 255.255.255.0

Give all the necessary confirmations and close. Open a browser and type the address 192.168.20.10, which is the default address of the board. You will see the page to confirm that everything is working fine. This page confirms that on the board is activated a web server “lighttpd”, a “light” version of the web server and there are a couple of interesting applications: “Codiad Web IDE” and “Linux Command Prompt”. The applications are accessible from the home page just opened. The userid and password to be used are indicated in the page itself. As easy as that.

The first is an IDE for development and management of multi language projects that will be very useful in our implementations. To access it, click on the blue button “Codiad Web IDE.” On the next page we insert given userid and password to get the page. As we see, the structure is typical of an IDE. In the upper left corner, the Explore window allows you to browse files and folders that belong to the www folder. The frame at the bottom left allows us to manage projects, while the large window on the right allows editing code. You can highlight the syntax of code by setting the correct language, by selecting it in the rich list that opens by clicking on the

“language tab” in the contextual menu bar at the bottom. You can split the window into different sections and the merge content between two windows.

The second application is a remote terminal via the web. You must sign in with the general user, “acme” in our case. Once inside we have a terminal window useable remotely. As an example, we gave the command that allows us to verify the occupation of partitions:

df –h

The thing is not accidental. The characters “-” and “+” must not be typed using the normal keyboard but the numeric keypad, or, if you use a laptop as it is in our case, obtained with the key combinations that emulate the numeric keypad. In our case simultaneously pressing the “Fn” and “-” associated with the matrix “Fn”. To use the user “root” you must type the command “superuser”

su

and then type root password (“acmesystems”).

These two applications allow us to handle almost the entire board remotely. We continue to analyze the different possibilities to connect the board, via SSH server and via serial console with the module DPI. We check the presence and operation of the SSH server with the command

service ssh status

The response confirms that the server is installed in the default configuration and is activated at boot. We connect using the remote terminal “PuTTY” and the remote File Manager application “WinSCP”. The operating system is virtually the same used with Raspberry Pi. To connect with both applications use the board address 192.168.10.10. We execute the login with userid and password and get visible results.

We take advantage of file manager to anticipate a topic that will be essential for the next configurations and customizations. We go to the folder / boot that “points” to the boot partition, and is mounted automatically at boot and let us verify its content.

Two files are particularly important. The zImage is the image file of the Linux kernel. It is the result of any compilation processes to customize the configuration of operating system according to our needs. In the website of Acme Systems are available pre-compiled kernel for specific requirements, as if we would enable the analog to digital converter. The file “acme-arietta.dtb” contains the pin configuration obtained from the “web” configurator.

Now let’s go back a moment to the terminal emulator connected to the serial “console”. We can use this window as a window terminal, with some limitations that we will see case by case. The main use of the console is to display all the messages output at boot and shutdown of the system. After login with userid “root” and password “acmesystems” try to give a command:

reboot

You will see that the console does not disconnect, as do the connections via the SSH server. To see the boot messages from the start, just make the connection before powering the board from the micro USB connector. Now we explore the management of GPIO. To know the meaning of the GPIO pins of Arietta G525 the best tool is the Web configurator.

In the basic version we see the default configuration of the GPIO pins. By clicking on any of the pin at the top right of the page we see the description of the pin function. For some pins, instructions to access, read and modify the content of pin are also given. If we want to customize the pin configuration we can use the configuration section on the right of GPIO representation, under the pin configuration. The configuration is done by selecting with a check mark the functions you want to enable. If you do some test, you can verify that some functions share the same pin as ADC and PWM, that share pin 34. 36, 38 and 40. Therefore, we can choose only one of the options, mixed configuration of these pins will not be accepted. Another case is the I2S bus, which requires the simultaneous activation of the I2C bus. In our case, we opted to activate the bus i2c-0 and the ADC.

Obtained the configuration we want, we request the preparation of the customized file .dtb by clicking on the button “Generate acme-arietta.dtb”. After creating the file is being proposed a link to download the file on your PC. Now we invite you to check the “Tutorial” site to see if additional steps are necessary. In the subsection “Using the A / D converter lines” we find a surprise. In the Linux image distributed with Arietta G25 is not present the driver Atmel ADC so it must be enabled using the “menuconfig” (see appendix to the book mentioned) and recompile the Kernel. Fortunately in the tutorial there is provided a link to download a pre-compiled kernel that includes the required driver. We download it to a folder on your PC. Now we have to update the boot partition of our board with the two files we downloaded. We decided to use the tool WinSCP that allows us to move and swap files between the board file system and PC.

First we create a backup folder on your PC, move the original files zImage and acme-arietta.dtb to the backup folder. We mount in acme-arietta.dtb the configuration file that we downloaded from the Web configurator. Move the zImage and acme-arietta.dtb to the boot folder. Well check the file names and their presence in the folder. Now we go to the console window and type the command:

We can also connect a trimmer 4,7KOhm and try to acquire the digital values at different positions of the trimmer cursor, obviously using the command corresponding to the channel ADC to which we connected the trimmer, the first in our case. We should always remember not to exceed 3.3V input to each pin, otherwise we will destroy the board. The inputs of the SoC AT91 DO NOT tolerate voltages above 3.3V.

We see now that we have activated the I2C bus. As a first test of his presence we’re going to verify the presence of the device files in /dev. Effectively we find the file i2c-0, indicating that the configuration operation is successful.

To manage and control at best the I2C bus we should install the i2c-tools package, which is part of the repository of the distribution. To do this we must connect the board Arietta G25 to Internet. At the moment we can use wireless WiFi. We have already connected the module to the board, so we just have to configure the file / etc / network / interfaces to work with our network. In figure is visible a FACSIMILE file. In fact the essential parameters to configure are those for the SSID, type of protection and password. For a connection with WPA you can use the example shown, of course entering the parameters related to your network.

Once connected to the local network we can install the package i2c-tools, or all of the packages that we want. We update the database package, and the distribution itself, with the commands:

apt-get update

apt-get upgrade

Then we install the package with command:

apt-get install i2c-tools

that will give us the results as shown in figure. Just a warning. You have to give the command from a terminal window open with PuTTY, or from the web terminal “Shell in a box”. If you give the command from the serial console terminal, you will get error messages. Do not be alarmed … and change window.

At this point we can say to have made acquaintance with the board Arietta G25 and the principal ways to access and manage it. The value of this board is that it allows to increase your skills in embedded GNU / Linux pretty easily, by guides and tools provided by manufacturer Acme Systems, which make the learning process even entertaining, without the “frustration” often accompanying those who goes deeply into GNU / Linux without proper guidance. For now, if you are going to base your future, even in part, by focusing on the digital evolution of our world, do not miss this opportunity.