Introduction

In previous exercises we learned how to program realtime programs with Xenomai. In this exercise we want you to use the learned techniques to program a piece of real hardware : a programmable LED clock.

Objectives

The primary objectives of this exercise are:

• To get experience with realtime programming with real hardware.
  
• To read the hardware specs and use this to correctly control the hardware to do what is desired according the program specs.

Description

                                

• a pendulum which contains 8 leds at its top, and is connected on a metal plate on its bottom. The metal  plate acts like a spring which makes the pendulum oscilate when you give it a sweep.
• a magnet which  drives the pendulum to oscillate. Note: on the pendulum is a small magnet attached.
• a led combined with a light sensor. The led-lightsensor combo is placed at the left side of the trajectory of the pendulum. When the pendulum swings and it passes the led-lightsensor combo it interrupts the led light. This interruption causes the light sensor to go from an high signal (lots of light) to a low signal (no light).

• The magnet makes the pendulum oscilate at a frequency around 9 Hertz.
• The light sensor  signal is connected to S6 of the parallel port.
• Because the light sensor is interrupted for a small time, the S6 signal will be like :   ---------___---------
  And since an interrupt is only generated when going from low to high we only will see the interrupt at the end of detection. Thus the led-lightsensor combo has a inaccuracy in detecting the position of the pendulum.  
• The leds are connected to the parallel port's data port as shown in the figure above. Note Dx=1 means led on, and Dx=0 means led off.
• The magnet is driving the oscilation. But when the pendulum is oscilating at high speed the magnet is only turned on for a small time of the period just to keep the pendulum going.
• The magnet is driving (turned on) only when the pendulum is going from right to left. Thus we would expect the motion from left to right go faster than the motion from right to left. However when the pendulum is oscilating at high speed the magnet is only turned on for a small time of the period, thus than we neglect that effect. Thus at high speed we have a symmetric oscilation.

Exercises

Exercise 11a.

Write a program to write a X on the LED clock. To keep it simple only write the X when the pendulum is going from left to right.

Exercise 11b.

Exercise 11c.