Unable to exit from LPM

Daniel Berenguer

Other Parts Discussed in Thread: CC430F5137

I have a simple program running on a CC430f5137 that was designed to exit from LPM3 after 10 seconds. This is the code simplified:

void main(void)

{

initCore(); // init CC430 core

PJDIR |= BIT1; // output pin to control LED

startRTC(10); // generate ISR after 10 seconds

PJOUT |= BIT1; // LED ON

__bis_SR_register(LPM3_bits + GIE); // Enter LPM3 with interrupts

PJOUT |= BIT1; // LED ON - This instruction is never called

}

__attribute__((interrupt(RTC_VECTOR)))
void rtcISR(void)
{

__bic_SR_register(LPM3_bits); // clears the bits corresponding to LPM3 and exits the low power mode

PJOUT &= ~BIT1; // LED OFF - This instruction is correctly executed after 10 seconds

}

The issue is that, even if the RTC ISR is called after 10 seconds, the MCU seems to never exit from LPM3. I've tried with other LPM modes with the same result. On the other hand, I remember having tested this feature with good results in the past so this has to be a simple detail.

thanks in advance for your ideas.

over 12 years ago

0 Steve W over 12 years ago

Intellectual 530 points

Daniel Berenguer said:
__bic_SR_register(LPM3_bits); // clears the bits corresponding to LPM3 and exits the low power mode

Did you not mean?

_bic_SR_register_on_exit(LPM3_bits);

Otherwise you will update the SR register which will then be overwritten with the previous value when you return from the interrupt.

0 Daniel Berenguer over 12 years ago in reply to Steve W

Expert 2185 points

Thanks Steve but I already tried with __bic_SR_register_on_exit with the same result. The MCU doesn't want to exit from LPM for some reason.

0 blb over 12 years ago in reply to Daniel Berenguer

Genius 3020 points

Hi,

It seems to me that the __bic_SR_register_on_exit would be the correct intrinsic to use. When you use this one what does the assembly generated look like? Is it modifying the SR on the stack?

Regards,

Barry

0 Steve W over 12 years ago in reply to Daniel Berenguer

Intellectual 530 points

So you say that even if the ISR is called it never returns from LPM, the 'on_exit' should fix that, but what are you expecting to see after the ISR has executed?

The ISR turns the LED off but then main turns the LED on and main exits, have you included a loop_forever that is not shown in your example?

0 Jens-Michael Gross over 12 years ago

Guru 227245 points

Daniel Berenguer said:
__bic_SR_register(LPM3_bits); // clears the bits corresponding to LPM3 and exits the low power mode

Inside an ISR, the LPM bits are already clear. But they are restored form stack on ISR exit. So you have to clear the bits in the stored copy of SR, with the __bic_SR_register_on_exit() intrinsic (or a similar one).

0 Leo Bosch over 12 years ago

Guru 23000 points

Try: __bic_SR_register_on_exit(CPUOFF);

0 Daniel Berenguer over 12 years ago in reply to Steve W

Expert 2185 points

Yes, there is an endless loop but it's not shown since it's never executed after __bis_SR_register(LPM3_bits + GIE). I also tried with __bic_SR_register_on_exit(CPUOFF) but nothing. In fact, LPM3 is defined as

SCG1+SCG0+CPUOFF in cc430f5137.h.

I'll try to do a disassembly tomorrow. I'll also try with a different compiler.

Thanks guys for your time!

0 Daniel Berenguer over 12 years ago in reply to Daniel Berenguer

Expert 2185 points

Sorry guys, the problem was relate to the WDT, that was not re-enabled after exiting from LPM.

Thanks so much.

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Unable to exit from LPM