CCS/MSP432P401R: Entering/Using low power mode 3

Hi Alex, 

Yes, with the SDK example which uses the TI APIs I was getting over two months of battery life. With my original code I was getting much less. I wanted to do it by using the registers.

I finally figured out the issue yesterday. I did not set all the gpio pins to conserve power. 

/*
 * Fixed 8/8/2019
 * Issue stemmed from GPIO pins not set to conserve power.
 *
 * After build, testing while in free run mode yields 2 months and 26 days of battery life
 * - build code
 * - open debug session
 * - run menu -> click restart
 * - run menu -> free run
 *
 * Close debug session and use energy trace (icon next to flashlight) and run
 * - results more than 5 years of battery life
 *
 * Changing to use VLO instead of LFXT changes battery life to years!
 */

#include "msp.h"

#define INT_WDT_BIT (1<<3) // used to turn on WDT interrupt
void GPIO_Init(void);
void set_WDT(void);
void low_PWR(void);
void set_CLK(void);
void set_PSS(void);
void set_AM(void);

void main(void)
{
	WDT_A->CTL = WDT_A_CTL_PW | WDT_A_CTL_HOLD;		// stop watchdog timer
	set_WDT(); // change WDT to interval timer, which will wake at end of timer run and repeat
	GPIO_Init(); // turns off all gpio to save power
	set_PSS(); // turn off SVSM
	set_AM();  // set active mode to low freq and vcore 0
	low_PWR(); // set low power mode for LPM3
	set_CLK(); // set clock to low freq, 32ish khz

    __enable_interrupt(); // enable interrupts. should wake when WDT interval completes

    while(1)
    {
        // will loop in here, do nothing.
        // when WDT triggers, will wake up and then interrupt will put system back to sleep.
        __WFI(); // put system to sleep
    }
}

void GPIO_Init(void) // turns off all gpio
{
    // This works. 16 bits total per register.
    // PA is P1 & P2 which is 8 bits a piece, and PB is P3 & P4, etc. This code now works.
    // enables pull-up/down resistor on all ports
    PA -> REN |= 0xFFFF;
    PB -> REN |= 0xFFFF;
    PC -> REN |= 0xFFFF;
    PD -> REN |= 0xFFFF;
    PE -> REN |= 0xFFFF;
    // sets direction of ports to outputs
    PA -> DIR |= 0xFFFF;
    PB -> DIR |= 0xFFFF;
    PC -> DIR |= 0xFFFF;
    PD -> DIR |= 0xFFFF;
    PE -> REN |= 0xFFFF;
    // sets all ports to use pull-down resistor
    PA -> OUT &= 0x0000;
    PB -> OUT &= 0x0000;
    PC -> OUT &= 0x0000;
    PD -> OUT &= 0x0000;
    PE -> OUT &= 0x0000;
}

void set_CLK(void) // sets up LFXTCLK
{
    // PJ needs to be enabled to use LFXTCLK
    PJ->SEL0 |= 0x03; // PJ only found by accident. Pg 8 of tech ref
    PJ->SEL1 &= ~0x03;
    CS->KEY = CS_KEY_VAL;   // enter key to allow for clk change. Cannot bitmask
    CS->CTL1 = 0; // set everything to 0, which makes lfxtclk the source. Check this reg is 0 after writing to it.
    CS->CTL2 = 0; // Lowest drive strength and current consumption LFXT oscillator
    CS->CTL2 |= (1 << 8); // set enable low freq clk
    CS->CLKEN &= (0<<0) | (0<<1) | (0<<2) | (0<<3); // shuts off clocks ACLK,MCLK,HSMCLK,SMCLK

    // sometimes doesn't work. Need to stabalize
while(CS->IFG & (1 << 0)) // loop until the low freq clock is stable
    {
        CS->CLRIFG |= (1 << 0);
    }
    CS->KEY = 0; // stop making clock changes
}

void set_WDT(void) // sets up WDT to interval mode for use in LPM3. This will wake up from LPM3 when timer loops
{
    // sets WDT to wakeup from sleep mode
    // WDT_A_CTL_IS_1 1 hour and 8ish minutes
    // WDT_A_CTL_IS_2 4 min 16 sec
    // WDT_A_CTL_IS_4 1 sec
    // WDT_A_CTL_IS_7 1.95 ms
    WDT_A->CTL = WDT_A_CTL_PW | WDT_A_CTL_IS_1 | WDT_A_CTL_TMSEL;
    NVIC->ISER[0] |= INT_WDT_BIT;
}
void WDT_A_IRQHandler (void)
{
    // what happens when the watchdog timer triggers
}

void low_PWR(void)
{
    // sets up low power mode 3 LPM3
    /////// Core 0
    SCB -> SCR |= (1 << 2);  // sleep bit to premp
    PCM->CTL1 = PCM_CTL1_KEY_VAL | (1 << 2); // force entry to LPM3
    // PCM->CTL0 = PCM_CTL0_KEY_VAL | PCM_CTL0_AMR__AM_LF_VCORE0; // set to low power mode 3
    PCM->CTL0 = PCM_CTL0_KEY_VAL | PCM_CTL0_LPMR__LPM3; // set to low power mode 3
    // PCM->CTL0 = PCM_CTL0_KEY_VAL | PCM_CTL0_AMR__AM_LF_VCORE0 | PCM_CTL0_LPMR__LPM3;
    while(PCM->CTL1 & 0x00000100) //makes sure PCM is not busy
    {
        // wait to stabilize
    }
}

void set_PSS(void) // turns off SVSM
{
    PSS ->KEY = PSS_KEY_KEY_VAL; // opens access to PSS
    PSS ->CTL0 |= PSS_CTL0_SVSMHOFF; // Turns off SVSM
    PSS ->KEY = 1; // closes access to PSS
}

void set_AM(void) // sets active mode to low freq and vcore 0
{
    PCM->CTL0 = PCM_CTL0_KEY_VAL | PCM_CTL0_AMR__AM_LF_VCORE0;
    while(PCM->IFG & (1 << 2)) // makes sure active mode does trigger a flag.
    {
        PCM->CLRIFG |= (1 << 2);
    }
    while(PCM->CTL1 & 0x00000100) // makes sure PCM is not busy after active mode change.
    {
        // wait to stabilize
    }
}