Hi

I needed to create a simple delay subroutine by using dummy loops. I
found some calculations and tested/working codes for LPC2148 on the net.
Three of them are:

Code:
void delay_ms(long int ms)
{
long int i, j;
for(i=0;i for(j=0;j<6553;j++);
}


OR

Code:

void delay_ms(unsigned long int count1)
{
unsigned int i,k;
k=count1*2600;
  for(i=0;i<k;i++);                     // Loop Decrease Counter
}



OR

Code:

void delay_ms(int x)         //this isn't accurate right
now{               //it's just a rough delay   int a,b;
for(a=0;a<x;a++){      for(b=0;b<3000;b++);   }}


Well, these supposed to be work but they do not.

I do something like this:


Code:

while (1) {
IOSET1 = 0x01000000;      // turn off LED
delay_ms(10);
IOCLR1 = 0x01000000;      // turn off LED
delay_ms(10);
}




I already made port direction settings etc.before this piece of code. It
is working correctly. But delay_ms() seems not become compiled because I
see very short (around 300-500 ns) pulses using an oscilloscope.

I tried to use delay_ms( 10000) insead of delay_ms(10)... Nothing
changed.

Then I tried to increase i and j end values in delay_ms() function.
Nothing changed.

for instance
Instead of for(i=0;i for(j=0;j<6553;j++);
I tried for(i=0;i for(j=0;j<16553;j++);

pulse durations did not changed. The stranger thing is, I compared two
hex files byte by byte and they are identical! so 6553 to 16553 does not
change anything in code.

Then I thought may be the compiler does not compile dummy loops because
of optimization, I added some arithmetic calculations in loop:

Code:

for(i=0;i for(j=0;j<6553;j++)   a++;


nothing changed. It seems loops are not compiled. ?


I thought may be there is another delay_ms function in the search path
include files. I changed the name to my_delay_ms... Nothing changed.

Finally I did something like this:

Code:

void delay_ms(long int ms)
{
long int i, j;
 for(i=0;i for(j=0;j<6553;j++) {
      IOSET1 = 0x00000001;    // set P1.1... it is an unused pin. just
for testing
  }
}



after this delay_ms has effect (delay). Why It does not work and it has
no effect if I do not place a port operation inside the loop?

that looks like optimization. your loops and the used variables were
incremented only but never used for read access.

put your variable a as volatile and
   for(i=0;i for(j=0;j<6553;j++)   a++;
shall work.

Better would be use of a timer and compare that content with your delay
time. You will never know what your compiler does or if the sequnece is
cached (ARM7) and takes less time.

JL