Why delay loops are not working in mspgcc?

vinodstanur said:

I tried to put a delay loop using while loop, for loop etc...But I couldn't observe the delay...
Is the compiler optimizing the code? If so, how could I introduce a delay in mspgcc?
below code is not working

Click to expand...

Delay loops are very sophisticated routines. Developers often do something like: int i = 1234;

while (i--);

or int i;

for (i = 0; i < 1234; i++);

NEITHER WILL WORK AS YOU EXPECT when optimisation is switched on!!! The optimizer will detect dead code in both examples and will eliminate it. It might even eliminate the loop completely. Adding the volatile attribute to the definition of 'i' might help, but don't count on it if 'i' is a local variable. The compiler can still detect the calculations are wasteful, and eliminate them.

Click to expand...

static void __inline__ brief_pause(register unsigned int n)
{
__asm__ __volatile__ (
"1: \n"
" dec %[n] \n"
" jne 1b \n"
: [n] "+r");
}

Click to expand...

__delay_cycles(unsigned long numOfCycles);

Click to expand...

This is one you'll find in pretty much every MSP430 tutorial or example, but yet it continues to bite people. At power up, the processor's watchdog timer, a device which resets the processor if it thinks that the firmware has locked up or entered an infinite loop, is enabled. This means that after booting, you only have a few thousand processor cycles to "service" the watchdog, which is the technical term for telling it that your application is still making progress.

The most common error to make with respect to the watchdog timer is simply ignoring it. If this happens, the device will reset itself over and over, as the watchdog timer expires after each boot.

Disabling the watchdog timer at bootup is the simplest way to deal with this. For "real" applications you likely want to configure and reenable the watchdog, but for learning it's OK to simply disable it and leave it disabled. Fortunately, disabling the watchdog is easy to do, and accomplished with this single line of code:

Code:

WDTCTL = WDTPW | WDTHOLD;

WDTCTL is the watchdog control register. WDTPW is a special constant, the "watchdog timer+ password". Any value written to the watchdog control register without this password will be ignored and trigger an error condition, so make sure you include it when manipulating the timer. The WDTHOLD bit disables the watchdog timer.

Click to expand...