Delay loop in C

Hi all,

I am using Keil C and 8051 (12MHz Xtal). I am wondering how do I calucate the delay time. For example,

void delay (int ms)
{
char k;
while (ms--)
{
for (k=0, k < 120; k++);
}
}

thanks,


Harrison

I doubt you can calculate the delay fully, as you do not know exactly how
the compiler will code it.

The practical method is to time a known number of loops, then adjust
until it is correct.

In C programs you cannot be sure of delay, coz it depends on compiler how it optimize the loops as soon as you make changes in the options the delay changes.

to test delay of the above loop try putting breakpoint before and after calling the function delay, and see how much time it consumed.

..
delay();
..

simulate on keil simulator with xtal 12Mhz. and see the results.

Hi,

Thank you for your reply. But how do you measure the time. Don't tell me to use a watch timer. We are talking about ms or us.


Harrison

Thank you for your reply. But how do you measure the time. Don't tell me to use a watch timer. We are talking about ms or us.

Harrison

Use a stopwatch
but do a test that executes thousands of loops and divide the result.
For critical timing you may need to use a hardware timer.

Using a simulator you can count the number of instruction cycles used in a single loop.

u'll have to use Timers for making exact delays..... it duznt matters whether u need delays of ms , us or even seconds...


below is a function of 1 second using timers.....


// the idea is to make a 50ms delay and run it 20 times as 20x50ms= 1000ms= 1sec

delay_1s() // timer of 1 sec
{
int d;
for(d=0;d<=20;d++)
{
TMOD=0x01;
TL0=0xFD;
TH0=0x04B;
TR0=1; // start timer.
while(TF0==0); // run until TF turns to 1
TR0=0; // stop timer
TF0=0; // reset the flag
}
}

well i told you to run under simulator and look at timer. like in keil as shown in fig below.

well i told you to run under simulator and look at timer. like in keil as shown in fig below.

Ajay Bhargav

how can i use the simulator i didn't catch it
please can you explain it in more details

thank you

@ fares
use debug mode of keil
in debug mode automatically this window comes
by using F10 u can move next function and by using F11 u can move line by line
F10= step over
F11= step in

check videos in tutorial section on how to use keil... that might help you better