Programming embedded systems

Seminar 3

PROGRAM STRUCTURE

Dr. Tran Thanh Hung

Department of Automation Technology,

College of Engineering, Can Tho University

Email: tthung@ctu.edu.vn

Review

For software development, we have look on:• “super loop” architecture in Seminar 1• switch interface in Seminar 2

Are there other factors we need to consider?

Review

• No company can remain in business for a long time if it creates new code for every project, from the beginning

Code must be reusable • Embedded systems have a very long lifespan and

need to be maintained or updated, BUT:- Programmers change very often- No programmer can remember what he/she has written

for a long time

Code must be easy to understand and maintain

Outline

In this seminar, we will consider the techniques to support above features

• Project header

• Port header

• Code reuse

• Useful functions

Seminar objectives

At the end of this seminar, by referring the lecture notes, students will be able to:

• understand issues of maintainable and reusable

• create and use “project header”, “port header”

• develop software that can be reused for many projects

Project header

• Look at your program in Exercise 2.3• If the hardware was changed:- AT89C51 was used, instead of AT89S52- XTAL 4MHz was used, instead of 12 MHz

How do you modify your code?

Project header

1. Put all information about microcontroller in a “Project header” file/*--------- Main.H ---------*/#ifndef _MAIN_H#define _MAIN_H#include <reg52.h>#define OSC_FREQ 12000000UL#define OSC_PER_INST 12// Typedefs typedef unsigned char tByte;typedef unsigned int tWord;typedef unsigned long tLong;// Interrupts #define INTERRUPT_Timer_0_Overflow 1#define INTERRUPT_Timer_1_Overflow 3#define INTERRUPT_Timer_2_Overflow 5#endif/*---------End Main.H ---------*/

2. In your program (Main.C), put an include: #include <Main.H>

Example 3.1

/*--------- Main.C ---------*/

#include <Main.H>#define display P0

sbit K1 = P1^0;

//function prototypes

void delay(tWord ms);

bit get_switch_K1(tWord ms);

void main (void)

{ tByte count;

while(1){ if(get_switch_K1(20))

count++;

display = ~count;}

}

void delay(tWord ms){ unsigned int x, y; for (x = 0; x <= ms; x++) { for (y = 0; y <= 120; y++); }}

bit get_switch_K1(tWord ms) { bit return_value = 0; if (K1 == 0) //switch K1 pressed?

{ delay(ms); //debounce if (K1 == 0) //K1 still pressed?

{ while (K1 == 0); return_value = 1; } }

return return_value }

Port header

• Look at your program in Exercise 2.3• If the hardware was changed:

- SWs were connected to Port 3, instead of Port 1- LEDs were connected to Port 2, instead of Port 0

How do you modify your code?

If there are over 100 of times the program access to Port 2 and Port 3, how do you change the program to adapt with the hardware?

Port header

• Put all of port reference in a “Port header” file:/*--------- Port.H ---------*/

#ifndef _PORT_H

#define _PORT_H

#define SW_PORT P1

#define LED_PORT P0

sbit K1 = SW_PORT ^0;#endif

/*---------End Port.H ---------*/

• In the program, put an include:

#include <Port.H>• If the hardware changed, just modify the relevant definition in

the file Port.H

Code reuse

• In Exercise 2.3, you have written a segment of code to read the switches

• If the develop a new project, and you have to read the similar switches

How do you write a code segment for that job?

If you know a job needed for every project, how do you write code?

Code reuse: Design

Code reuse: Design

• Put code segments for each job or relevant jobs in separate files: one name.h file and one name.c file

• name.h file is a header file, consists of definitions and function prototypes for name.c file. This file must be added to the Source Group1 area in KeilC window

• name.c file consists of all code segment for the job. This file must be added to Source Group1 area in KeilC window

• Put an include in name.c file and project’s main file:

#include <name.h>

Exercise 3.1

• Redesign your program in Exercise 2.3 so that code segment for reading 8 SWs on Port 1 can be reused in many other programs.

• Follow the rule for noting

/*******************************************************************************

* @fn getSwitch

* @brief Read switches

* @param void

* @return 0,1,2,3,4,5,6,7 if SW0..SW7 is pressed,

* 0xFF if no SW is pressed or pass debounce process

*/

unsigned char getSwitch(void)

Exercise 3.2

• Redesign your program in Exercise 2.4 so that code segment for reading 4x4 keypad can be reused in many other programs.

• Follow the rule for noting

/*******************************************************************************

* @fn KeyScan

* @brief Read switches

* @param void

* @return ‘0’,’1’,…,’9’,’A’,…’D’ if corresponding key is pressed,

* 0xFF if no key is pressed or pass debounce process

*/

unsigned char KeyScan(void)

Exercise 3.3

• Write (game) program to do following things

- Let user choose a position (0-7) by pressing a SW on Port 1

- Turn on the first LED on Port 0 and let the LED ships from low to high position with a random of times

- If the LED stops at the same position that user chose, turn on a green LED on P2.7 (“You win”)

- Otherwise, turn on a red LED on P2.6 (“Sorry. Try again”). Notes:

*Use the function getSwitch in Exercise 3.1 to read the SWs

*Use function rand() in <stdlib.h> to create a random number