Delay function in C not delaying

Question

It is very strange problem because it should works but it doesn't. My task is to do a a simply function which delay a program.

So time before use a function

And after using a function: time after using I want to have a 1 second delay so i increased a number of iteration for 100000 (before 100) , but time hasn't change. after increasing iteration

why? it is logical that if i increase the number of iteration, the time should be longer...

EDIT:

#include <LPC21xx.H>

void Delay(){
    long int i;
    for(i=0; i<48000000000;i++){
    }
}

int main(){
    //set pin 16 P1 as out
    IO1DIR = 0x10000;
    //set pin 16  P1 on 1
    IO1SET = 0x10000;
    Delay();
    //set pin 16 port P1 on 0
    IO1CLR = 0x10000;

}

I use a uVision Keil.

Please include the source of your program in your question, formatted as code (highlight it and use the "{}" button). Pictures of text are far less useful. — Keith Thompson, Feb 28 '19 at 19:44
I'm pretty sure your C compiler will see that cycle as doing nothing and just skip foward. To make sure the cycle is executed put something like int a=0; inside the cycle. That way the compiler will not ignore the cycle. — H. Figueiredo, Feb 28 '19 at 19:55
Here are 2 ways you may do this: 1. Use the _nop_ () function to insert a number of NO-OP instructions into your C code. Figure out the amount of time it takes for a single NOP on your target and use as many as necessary. 2. Create a function that starts a timer that generates an interrupt on overflow. The interrupt sets a flag that the function waits for after starting the timer. When the flag is set, the function stops the timer and returns. Source: http://www.keil.com/support/docs/606.htm code: https://stackoverflow.com/questions/21553964/how-to-create-a-delay-function-in-keil-uvision — Horacio Goetendia, Feb 28 '19 at 20:01
@H.Figueiredo I did this and the time of executing a loop in 100 iteration is 10-7 s and in 1 000 000 iteration is the same... what is wrong with this? — Always Dissapointed, Feb 28 '19 at 20:01
@HoracioGoetendiaBonilla I am a little confused about this information and i still don't know how to cope with this problem. — Always Dissapointed, Feb 28 '19 at 20:05
@KrzysztofBolek Use volatile int a=0; Volatile will force the compiler to evaluate the variable each time, instead of trying to optimize. But you have an answer from Horatio, maybe you prefer his answer. — H. Figueiredo, Feb 28 '19 at 20:18
@H.Figueiredo The compiler will probably see that the variable `a` is never used, either, and will eliminate it, too. — FredK, Feb 28 '19 at 20:18
@FredK if its volatile I think the compiler is forced to not skip it. https://stackoverflow.com/questions/7083482/how-to-prevent-gcc-from-optimizing-out-a-busy-wait-loop — H. Figueiredo, Feb 28 '19 at 20:19
What size is `long int`? 48000000000 is far too big for 32 bits. — Dipstick, Feb 28 '19 at 20:40

Horacio Goetendia · Accepted Answer · 2019-02-28T20:34:35.390

0

Use the nop () function to insert a number of NO-OP instructions into your C code. Figure out the amount of time it takes for a single NOP on your target and use as many as necessary. Source: keil.com/support/docs/606.htm

For this "sample" y try with Delay(1000) you can make changes to this value;

#include <LPC21xx.H>
#include <intrins.h>

#pragma O0
void Delay(volatile uint32_t cnt) {
    while(cnt--)
        _nop_();
}

void DelayWithoutNop(volatile uint32_t cnt) {
    while(cnt--);
}


int main(){
    //set pin 16 P1 as out
    IO1DIR = 0x10000;
    //set pin 16  P1 on 1
    IO1SET = 0x10000;
    Delay(1000);
    DelayWithotNop(3000);
    //set pin 16 port P1 on 0
    IO1CLR = 0x10000;

}

edited Feb 28 '19 at 20:34

answered Feb 28 '19 at 20:13

Horacio Goetendia

183
1
8

It can be do in a simpler way? And in instruction in my homework i must use a for loop, so the _nop_(); is too advanced for my class level of programming. – Always Dissapointed Feb 28 '19 at 20:17
I added a function DelayWithotNop with a simple operation, in this case you have to test it with the right value to reach 1 second of delay based in your current hardware – Horacio Goetendia Feb 28 '19 at 20:27

Delay function in C not delaying

1 Answers1