ECE 341 Lab 5
Preemptive Real-Time Control
Revised (9/24/2009)
Purpose
The purpose of this lab is to incorporate the concepts investigated in the past four
laboratory exercises to implement a process control system to control the speed of
rotation, direction and step mode of a stepper motor using full preemptive real-time
control with prioritized interrupts.
Concepts
Embedded systems best coding practices usually mandate that interrupt service
routines be kept as short as possible. For this exercise, all processes will be initiated from
within one of the two interrupt service routines. After initialization, the main loop will
consist of the statement, “while(1);”.
The specifications are present in revolutions per minute (RPM). However, this
must be translated into steps per second that then can be implemented by executing a
delay between steps. What is needed is an equation that converts the specified RPM to a
time delay. Fortunately (for you) I have selected rotational speeds the convert in even
multiples of milliseconds. A step frequency in steps/sec is easily computed using the
appropriate conversion factors. The inverse of this frequency is the delay period. Include
the equation that you used to complete Table II in your report.
Assignment
You will be mapping the two inputs on BUTT2 and BUTT3 to stepper motor
mode, direction, and speed control described in Table I. Implement a 1ms delay based on
Timer A2 interrupts for stepper motor speed control.
Implement an external interrupt where Button 2 and 3 will generate external
interrupts on bits 5 and 6 of the returned data when the PCF8574_IOX_Rd(IOX_PORT0)
function is called. The example external interrupt code discussed in class and provided at
http://www.ece.uidaho.edu/ee/classes/ECE341/lab5/IOX_Interrupt.c should be used to
serve as an aid in developing the external interrupt ISR. The student are expected
thoroughly understand the functions provided as examples before attempting to use them
in a program for lab exercises.
The following list of requirements must be implemented in your code:
Implement a fully nested interrupt scheme with timer A2 interrupts set for level 2
priority and the push button interrupts set for level 1 priority.
Tasks executed in the “main” function
oBoard initialize to setup IO ports G and F
oInitializes the RCM 3000 system for external interrupts
See Part 2 of Chapter 5 of the ECE 340 course notes http://ee.uidaho.edu/
ee/classes/ECE340/notes/notes.htm
see http://www.ece.uidaho.edu/ee/classes/ECE341/lab5/IOX_Interrupt.c
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