OS - Phidget SBC

On the Single Board Computer (SBC), Phidgets can be either plugged directly into one of the USB ports or run over a network using the Webservice.

Getting Started (Libraries and Drivers)

The SBC is a unique Phidget. It is a computer with a Linux operating system. It can compile code, save files, manage background jobs, host information over the web, and more.

To learn the basics about the SBC, we have a handy web interface to interact with the SBC. This is covered in detail on the Getting Started Guide for the SBC. So before reading this page on how to use the operating system, you should have done the following via the Getting Started Guide:

• Set up networking on your SBC, via either Ethernet or wireless
• Set up a password
• Learned the IP address or link local address of the SBC

Conceivably, you could simply use the SBC like any Linux computer, and do all of your development and compiling of Phidget code on the SBC itself. In practice this is quite complicated as the SBC does not have a keyboard or screen. So usually, you will want to develop your code on an external computer and copy files and settings over to the SBC via a network. This makes this Getting Started section unique, in that we show you how to set up both computers:

• Your External Development Computer, usually your main desktop or laptop which will transfer files and settings to and from the SBC
• The SBC, with programming language libraries

Getting Started - External Development Computer

The simplest way to transfer files and commands to and from the SBC is via a program called ssh. The ssh program provides command line text access over a network into the SBC. Using it, you can run programs and give the SBC commands. The ssh program has a companion program called scp which can copy files back and forth. For Linux users, this will be familiar territory. If you are using Windows or Mac OS, and are unfamiliar with ssh, you can think of it like the command line or a Mac terminal.

Before connecting over ssh, you will need:

• The IP address (such as 168.254.3.0) or link local address (such as phidgetsbc.local) of the SBC
• The admin password for the SBC

Both of these items can be found by following the steps in the Getting Started Guide for the SBC.

SSH on Windows

The ssh program is not installed on Windows by default. But, there are a variety of SSH programs available for free, one simple and commonly used program being [PuTTY].

With PuTTY, when you first run the program it will ask you what to connect to. Enter the IP address or link local address of the SBC, and then click the SSH radio button right below the address, which will change the port to 22. Then click open, and you'll have an ssh connection to the SBC open in a terminal. It will prompt you for a user name (root) and password (the admin password).

To copy files back and forth, there is an SCP component to PuTTY, called PSCP, which is available from the same [PuTTY download page].

SSH on Linux and Mac OS

Linux and Mac OS already have ssh installed by default. To run ssh simply open a terminal...

• Ctrl-Alt-T on Linux
• Applications → Utilities → Terminal on Mac OS

...and type:

ssh root@phidgetsbc.local

If you have re-named your SBC, include that name instead of the phidgetsbc.local link address. Or, you can use the SBC's IP address, e.g. ssh root@168.254.3.0.

To copy files back and forth, the command follows the form of: scp from to

So, to copy a file /root/data.txt from the SBC to your local machine, type:

scp root@phidgetsbc.local:/root/data.txt .

Note the use of the dot . to indicate that scp should put the file in the current local directory. If you're not sure what folder the terminal is operating in type pwd to print the working directory. Terminals usually start by default in your home folder.

Getting Started - SBC Debian Linux

Installing Python

Installing Python has two steps. First, you'll need to install the basic ability to run python, and then you'll need to install the Phidget Python module.

Basic Python

apt-get install python

Method 1: Use a USB Key

Copy the [| Python Libraries] onto a USB key. Insert the key into the SBC.

Copy the web link address for the Python Libraries from the Python Language Page.

Then you can either copy http://www.phidgets.com/downloads/libraries/PhidgetsPython_2.1.8.20120216.zip

Using SBC Linux

Now that you've set up communication with the SBC, and installed whichever programming language support you need, you're probably ready for a short tour of useful tools on the SBC's version of Linux.

First, unless you set up another user, you will be running on the SBC as root, which is the super-user. For experienced Linux users, this probably makes you nervous because you know you can overwrite important system files without the system asking for additional permission. Even as a Windows or Mac OS user - although you may usually run your computer as an administrator - the system usually prompts you to confirm before you do anything really dangerous, and this will not happen as root.

Some Useful Commands

ls

pwd

nano

apt-get

Some Useful Commands to Install

gcc

less

wget

unzip

python

Troubleshooting

If the examples do not work but USB does work (i.e. your computer can consistently see the device in the hardware), take a moment to check the basics:

• No other programs, drivers, or processes are using that USB port in software
• You are running the example program as root (or your udev rules have been set properly)
• You are using libusb 0.1 (not 1.0 or later)
• You have compiled versions of libphidget21.a and libphidget21.so in your system library location (usually /usr/lib)
• The Phidget libraries are the latest version (visit the getting started section to download them)
• Your Linux kernel version is 2.6 or later (type uname -r in a terminal to get your kernel version)
• Check the common problems section below, some specific combinations can cause problems

If your problem doesn't seem to be fixed by these steps, make sure that the Phidget is seen consistently by USB (if it is erratic, try our general troubleshooting guide). If you are still having problems after the troubleshooting guide, please ask us!

Programming Languages

Now that you have the basic libraries installed, you can pick your language and begin programming!

If you are not using the webservice (discussed below) to control a Phidget over a network, your next step will be to delve into the use of your specific language. Each page has its own set of specific libraries, code examples, and setup instructions.

On Linux, we recommend the following languages:

• C/C++
• Java
• Python

Common Problems and Solutions

Low Speed Phidgets (Max of 8): Linux will only schedule one low-speed interrupt transfer per millisecond.

You can find out the type of your Phidget by attaching it and then running dmesg | tail, which will display the type of Phidget from your kernel logs, as described above in the hardware section. The practical consequence of this is if your system has many low speed Phidgets attached, they will each be throttled down. Low speed Phidgets require an interrupt transfer as often as every 8 milliseconds. A Linux system could only have up to 8 of these Phidgets attached.