watchdog interval timer low power mode problem

Mike Asker

Prodigy 20 points

Other Parts Discussed in Thread: MSP430G2231

Hi,

I'm having a problem getting the Watchdog interval timer ISR to work while keeping the CPU clock running.

I'm using a msp430g2231 on the Launchpad and compiling using mspgcc

Here's my code:

////////////////////////////////////////////////
#include <msp430.h>
#include<signal.h>
#include "msp430g2231.h"

/*WDT interval timer- code based on msp430 examples*/
//compiler=mspgcc


void main(void) {
  P1DIR |=BIT0;                       // Set the Launchpad redled P1.0 as an output pin    
  //BCSCTL3 = LFXT1S_2;               // use the VLO for ACLK
  WDTCTL = (WDTPW+WDTTMSEL+WDTCNTCL); // setup watchdog register as interval timer (same as WDT_MDLY_32)
  IE1 |= WDTIE;                       //enable watchdog interrupt
  _BIS_SR(LPM0_bits + GIE);           //set LPM0 mode and enable interrupts       **** WORKS ****
  //_BIS_SR(GIE);                     //keep cpu running and enable interrupts    **** DOES NOT WORK ****
}//end of main

//interrupt service routine
interrupt(WDT_VECTOR) watchdog_timer(void)
{
  P1OUT ^= BIT0;
}//end of interrupt
////////////////////////////////////////////////////

The line

_BIS_SR(LPM0_bits + GIE);

works, the interval timer runs and the correctly, but it shuts off the cpu and I want to keep the main cpu running and do other stuff

So if I use

_BIS_SR(GIE);

The interval timer fails to run.

I tried resetting the interrupt flag inside the ISR with

IFG1 &= ~WDTIFG;

But that didn't help.

I couldn't find any reference to this behavior in the documents.

Does anyone know how can I run the watchdog interval timer with the CPU clock still running?

cheers

-mpymike

over 12 years ago

0 Robert Cowsill over 12 years ago

Guru 16361 points

When you use "_BIS_SR(GIE);" the CPU stays awake and execution of main continues. Unfortunately there's no further code after that point, so he CPU runs off the end of main().

I'm not sure whether that would cause the problems you're seeing, but it's worth eliminating the possibility. Try adding a "while(1);" infinite loop after the "_BIS_SR(GIE);" to see if that fixes the problem.

0 Mike Asker over 12 years ago in reply to Robert Cowsill

Prodigy 20 points

Thanks for the quick answer Robert! Adding the 'while' loop made it work.

Its sounds obvious now that you explained it.

What confused me is that I just tested out a pin interrupt ISR. It had a _BIS_SR(GIE) and no while loop,
it also must of run off the end of main. But it continued to work and generate interrupts.

I think I will be adding 'while' to all my main's

thanks again

-mpymike

0 Jens-Michael Gross over 12 years ago in reply to Mike Asker

Guru 227245 points

Mike Asker said:
What confused me is that I just tested out a pin interrupt ISR. It had a _BIS_SR(GIE) and no while loop,
it also must of run off the end of main. But it continued to work and generate interrupts.

Apparently there is some 'end of operation' code behind main added by your linker (whether there is such code is linker-specific and differs between IDEs). Probably this code deactivates the watchdog , so it won't reset and restart the MSP when main doesn't trigger the WDT anymore. Also, it may enter LPM4 for low power, and having the WDT active would keep the WDT clock active and raise power consumption. But port interrupts will still execute as they don't need and clock.

Just a possibility as I never really looked at the different after-main codes of CCS, IAR or MSPGCC.

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watchdog interval timer low power mode problem