CCS/MSP430G2553: How can I use LPM3 to generate a delay and wake up to some task

Hi Preetham,

You need to use a timer with a global counter to achieve this, as in G2553 there isn't any timer itself can support up to 20mins single interval.

All you need to do is to initialize the global counter value in the main loop, tick it in the timer's ISR until the value you want, and then use "__bic_SR_register_on_exit(LPM3)" to exit LPM after the ISR.

Below shows a simple pseudo code for your reference. For the timer, you can use either TimerA or WDT+ in G2553, with ACLK as clock source.

in main loop:
{
    ...
    counter = 0;
    start_timer();
    __bis_SR_register(LPM3 | GIE);
    ...
}

in timer ISR:
{
    clear_timer_IFG();
    counte++;
    if(counter == SOME_THRESHOLD)
    {
        __bic_SR_register_on_exit(LPM3);
    }    
}

Regards,

Harry

Hi Harry,

Thank you so much.

1) With global timer can I achieve this ?

2) Do you have any sample or blog or anything to help me understand further on this ? Thank you for your time on this. 

Hi Preetham,

Yes, all timers in G2553 can achieve this.

You can refer to the lpm3 code examples in MSP430Ware.

I attached the code here for your reference.

You need to pay attention that in this code MCU wakes up every 4 second. You can adjust the timer interval and also put a global variables to count the wakeup times to achieve ~20 min.

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//******************************************************************************
//  MSP430G2xx3 Demo - Basic Clock, LPM3 Using WDT ISR, 32kHz ACLK
//
//  Description: This program operates MSP430 normally in LPM3, pulsing P1.0
//  at 4 second intervals. WDT ISR used to wake-up system. All I/O configured
//  as low outputs to eliminate floating inputs. Current consumption does
//  increase when LED is powered on P1.0. Demo for measuring LPM3 current.
//  ACLK = LFXT1/4 = 32768/4, MCLK = SMCLK = default DCO ~ 800kHz
//  //* External watch crystal installed on XIN XOUT is required for ACLK *//	
//
//
//           MSP430G2xx3
//         ---------------
//     /|\|            XIN|-
//      | |               | 32kHz
//      --|RST        XOUT|-
//        |               |
//        |           P1.0|-->LED
//
//  D. Dang
//  Texas Instruments Inc.
//  December 2010
//   Built with CCS Version 4.2.0 and IAR Embedded Workbench Version: 5.10
//******************************************************************************


#include <msp430.h>

int main(void)
{
  BCSCTL1 |= DIVA_2;                        // ACLK/4
  WDTCTL = WDT_ADLY_1000;                   // WDT 1s/4 interval timer
  IE1 |= WDTIE;                             // Enable WDT interrupt
  P1DIR = 0xFF;                             // All P1.x outputs
  P1OUT = 0;                                // All P1.x reset
  P2DIR = 0xFF;                             // All P2.x outputs
  P2OUT = 0;                                // All P2.x reset

  while(1)
  {
    int i;
    P1OUT |= 0x01;                          // Set P1.0 LED on
    for (i = 5000; i>0; i--);               // Delay
    P1OUT &= ~0x01;                         // Reset P1.0 LED off
    __bis_SR_register(LPM3_bits + GIE);     // Enter LPM3
  }
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=WDT_VECTOR
__interrupt void watchdog_timer (void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(WDT_VECTOR))) watchdog_timer (void)
#else
#error Compiler not supported!
#endif
{
    __bic_SR_register_on_exit(LPM3_bits);   // Clear LPM3 bits from 0(SR)
}