OS - Linux

From Phidgets Support
Revision as of 15:43, 6 January 2012 by Cora (talk | contribs) (→‎Software)

Phidgets can run on Linux directly using USB, or remotely over a network using the Phidget Webservice.

You need kernel version 2.6 or later.

Getting Started (Libraries and Drivers)

Linux does not have a graphical user interface to check your Phidget, but it does have a complete API for many languages.

For any language, you will need the basic Phidget Libraries for Linux:

Installing

To install the libraries, follow these steps:

  1. Download libusb-0.1 and its development libraries
    • Try apt-cache search libusb in a terminal to find current packages
    • Or install from source, which includes the libusb development libraries
  2. Unpack and install the Phidget Libraries for Linux (download above)
    • From the main libraries directory, run:
      ./configure
      make
      sudo make install
    • This will compile phidget21.h and place the library into your gcc path

Checking

To confirm the libraries were installed and work correctly, you can check both the hardware and software sides of the interface. It is worth checking the software side first, because if it works then you know the hardware side is also okay.

Software

To confirm that the libraries were installed correctly and can be used in code, you can use the Phidget C Examples:

Although the libraries are written in C, the libraries for Python, Java, and most other Phidget-supported languages depend on them.

The easiest way to confirm that the libraries got compiled correctly and installed in the right place will be to compile and run the HelloWorld C example. This does not involve writing any C code, but it does involve compiling the example and running it, as we show below. If you feel more comfortable running the HelloWorld example for your specific language, you can skip below and pick your language, but keep in mind that any problems could be with the C library installation and not necessarily with your language.

To compile and run the basic C example for checking your installation:

1. Unpack the Phidget C Examples (download above)
2. Open a terminal (often Ctrl-Alt-T) and go to the directory where the examples are unpacked
3. Compile the HelloWorld.c example:

     gcc HelloWorld.c -o HelloWorld -lphidget21

4. Run the HelloWorld example:

     sudo ./HelloWorld

(The sudo is needed for USB access for now)

The -lphidget21 will look in the standard library location for your Linux distribution (usually /usr/lib/) for the Phidget 21 library file.

Generally, libraries to be linked on Linux through gcc have a naming convention. For example, -lphidget21 looks for the binary files libphidget21.a and libphidget21.so in the library location (usually /usr/lib). These files are automatically put in the library location during the make install step of installing the libraries above.

The HelloWorld program will simply print out basic information for any device you plug in, and print a message upon unplugging the device. For example, starting the program, plugging in an Interface Kit Phidget, unplugging the Interface Kit, and pressing Enter displays: 

   $ sudo ./HelloWorld 
   
   Opening...
   Press Enter to end

   Hello to Device Phidget InterfaceKit 8/8/8, Serial Number: 37299
   Goodbye Device Phidget InterfaceKit 8/8/8, Serial Number: 37299

   Closing...

Hardware

If the out-of-the-box examples do not work, make sure the Phidget is seen by your USB interface. You can use the kernel log reader dmesg. Pipe the output of dmesg into the utility tail to simply read the last ten lines of the log: 

     $> dmesg | tail
     ....(9 lines)....
     [24344.013638] usb 2-1.2: new low speed USB device number 5 using ehci_hcd

The number between the [] is the system time in seconds since the last boot up, so you can tell whether the event was recent or not. (This will also tell you the interrupt type of Phidget that is registered by the USB interface, see the Linux page limitations section for more information on what this means.)

The Phidget should both connect and disconnect properly, so unplugging it should result in an additional line at the tail: 

     $> dmesg | tail
     ....(8 lines)....
     [24344.013638] usb 2-1.2: new low speed USB device number 5 using ehci_hcd
     [25094.809328] usb 2-1.2: USB disconnect, device number 5

If you don't see similar lines to these at the tail of your kernel log, take a look at the troubleshooting section below.

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 above 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 limitations section below, some specific combinations can cause problems

If your problem doesn't seem to be fixed by the steps above, 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:

You can also use these languages, but they do not support event driven code, and must use logic code only:

Webservice

The Phidget Webservice allows you to remotely control a Phidget over a network.
Before using these webservice drivers, it may help to learn about how the Phidget Webservice works.

Common Problems and Solutions

None yet, yay!

Maybe talk about udev rules?

Limitations

  • Linux will only schedule one low-speed interrupt transfer per millisecond. 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.
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