delay function

Charleston Melgar

Other Parts Discussed in Thread: MSP430G2553

Hello, I am using msp430g2553 and Im new to using it. I just want to know how is the delay being computed in this code. Can somebody explain the working principle of this delay function?Thanks :)

#include <MSP430G2553.h>
void delay430(void);
void main( void )
{
WDTCTL = WDTPW + WDTHOLD; // Stop watchdog
P1DIR = 0x41; // Sets P1.0 and 1.6 to output direction
while(1){ //Loop forever (always true)
P1OUT =0x40; //Set 1.6 to high (HEX)
delay430(); //delay function call
P1OUT =0x01; //Set 1.0 to low (HEX)
delay430(); //delay function call
}
}
//Delay function...??????
void delay430(void){
unsigned int i;
for(i=0;i<50000;i++); }

over 9 years ago

0 old_cow_yellow over 9 years ago

Guru 58965 points

There are many ways to implement a delay function.

In the code you cited, it is using a method very similar to what kids use in the "hide and seek" game (en.wikipedia.org/.../Hide-and-seek).

You make the CPU (the "it" in the child game) count from 0 to 49999; and that will take some time. So it stalled/delayed the CPU for that duration. This method has some disadvantages and might not even work. But you can ignore that for the moment and come back to it after you explored other areas of programming MSP.

0 Todd Anderson78572 over 9 years ago in reply to old_cow_yellow

Guru 14640 points

You could also check out
processors.wiki.ti.com/.../Getting_Started_with_the_MSP430G2553_Value-Line_LaunchPad_Workshop
an excellent free course.

0 old_cow_yellow over 9 years ago in reply to old_cow_yellow

Guru 58965 points

old_cow_yellow said:
... This method ... might not even work ...

Because some wiseguy might have told the "it" to cheat and not do the counting.

In programming, this is called "optimization", not cheating ;)

0 Dennis Eichmann over 9 years ago in reply to old_cow_yellow

Guru 74080 points

OCY always has the best explanations - love them!

Charleston Melgar said:

void delay430( void )
{
  unsigned int i;

  for( i = 0; i < 50000; i++ );
}

This delay works like this:

Enter delay function
Set i to 0
Is i < 50000? YES, it is 0, execute for-loop
i = i + 1 (changes from 0 to 1)
Is i < 50000? YES, it is 1, execute for-loop
i = i + 1 (changes from 1 to 2)
Is i < 50000? YES, it is 2, execute for-loop
i = i + 1 (changes from 2 to 3)
...
Is i < 50000? YES, it is 49999, execute for-loop
i = i + 1 (changes from 49999 to 50000)
Is i < 50000? NO, it is 50000, don't execute for-loop
Leave delay function

Dennis

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delay function