Embedded Linux Device Interfacing Workshop, Report

The target audience for this workshop, was primarily application developers, who would like to get their feet wet in the world of embedded Linux. So we decided to use Python instead of C, for the example code. But to accomodate people who were not familiar with Python, we had a few sessions introducing Python.

Now that people were comfortable with Python, we next moved on to, what Embedded Linux is all about. Deepak gave an introduction to Linux in embedded systems, and how to use an Embedded Linux system. Everyone tried connecting to the target, through the USB serial interface.

We then discussed about how the CPU talks to devices using Memory Mapped IO and Controller Based IO. This was followed by an introduction to driver in Linux, where we showed the power of the file abstraction in Linux. Vijay showed examples, with the mouse device, audio device, hard disk device, and CD-ROM device.

After laying a strong foundation on devices and driver, it was time to get started with accessing devices. The serial interface was presented first. Babu demonstrated the use of serial interface for communicating with a GSM modem. The DietIO board has a UART based LCD, that people tried accessing from the host. The I2C interface was presented next. Babu demonstrated how an I2C accelerometer can be accessed from the host. The add-on board has a I2C 4-way joystick, that people tried accessing by writing a simple Python script.

Now, not all devices are accessed through /dev interface, some devices are exposed throug /sys on Linux, especially GPIO, PWM and ADC. So Rashid, did a session on the sysfs filesystem, and showed how it differs from /dev and /proc. Rashid demostrated the utility of sysfs, with 3 examples: laptop backlight control, a custom ifconfig clone, and a partition table printing tool.

Deepak introduced GPIOs and their sysfs interface. The add-on board has an RGB LED that can be controlled through GPIOs, that people tried controlling using a Python script. Then GPIOs were used to read status of GPIO connected buttons.

After lunch, Deepak introduced PWMs and their sysfs interface. The add-on board has a buzzer that can be controlled through PWMs. People tried playing various tones on the buzzer, by controlling the frequency of the PWM signal. People then tried controlling the speed of the motor, by varing the duty cycle of the PWM signal. We connected motors, ripped from old CD-ROM drives, for the purpose of this exercise.

The next interface was ADC. Babu introduced the ADC and its sysfs interface. The add-on board has a Potentiometer and Light Sensor. People were able to read the state of the potentiometer and the intensity of the light using the sysfs interface.