[参考译文] 创建一小时的延迟

Resource Explorer 中有大量示例。 下面有一个(msp430fr235X_lpm4_5_02.c)使用 RTC 每秒生成一个中断(需要32K 的晶体)：

//******************************************************************************
//   MSP430FR235x Demo - LPM3.5, device enter LPM3.5 and toggles P1.0 with
//                       RTC interrupt handling every 1s
//
//
//   Description: Device enter LPM3.5 after configuring the RTC. The RTC wakes
//   the device up from LPM3.5 every second and toggles P1.0.
//   It also stores the state of P0OUT in the Backup RAM Registers.
//
//   ACLK = XT1 = 32kHz, MCLK = SMCLK = default DCODIV = ~1MHz.
//
//            MSP430FR2355
//         -----------------
//     /|\|                 |
//      | |                 |
//      | |        XIN(P2.7)|--
//      --|RST              |  ~32768Hz
//        |       XOUT(P2.6)|--
//        |                 |
//        |             P1.0|-->LED
//
//   Cash Hao
//   Texas Instruments Inc.
//   November 2016
//   Built with IAR Embedded Workbench v6.50.0 & Code Composer Studio v6.2.0
//******************************************************************************
#include <msp430.h>

void initGpio(void);

int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;               // Stop WDT

    initGpio();                             // Configure GPIO

    // Initialize XT1 32kHz crystal
    P2SEL1 |= BIT6 | BIT7;                  // P2.6~P2.7: crystal pins
    do
    {
        CSCTL7 &= ~(XT1OFFG | DCOFFG);      // Clear XT1 and DCO fault flag
        SFRIFG1 &= ~OFIFG;
    } while (SFRIFG1 & OFIFG);              // Test oscillator fault flag

    // First determine whether we are coming out of an LPMx.5 or a regular RESET.
    if (SYSRSTIV == SYSRSTIV_LPM5WU)        // When woken up from LPM3.5, reinit
    {
        // If MCU wakes up from LPM3.5, re-init and then return to LPM3.5 again.

        // Restore P1OUT value from backup RAM memory, keep P1OUT after LPMx.5 reset
        P1OUT = *(unsigned int *)BKMEM_BASE;

        __enable_interrupt();               // The RTC interrupt should trigger now...
    }
    else
    {
        // Device powered up from a cold start.
        // It configures the device and puts the device into LPM3.5

        // Configure backup memory
        *(unsigned int *)BKMEM_BASE = 0;

        // Configure RTC
        // Interrupt and reset happen every 1024/32768 * 32 = 1 sec.
        RTCMOD = 32-1;
        RTCCTL = RTCSS__XT1CLK | RTCSR |RTCPS__1024;
        RTCCTL |= RTCIE;

        // Store P1OUT value in backup memory register before enter LPM3.5
        *(unsigned int *)BKMEM_BASE = P1OUT;
    }

    // Enter LPM3.5 mode with interrupts enabled. Note that this operation does
    // not return. The LPM3.5 will exit through a RESET event, resulting in a
    // re-start of the code.
    PMMCTL0_H = PMMPW_H;                    // Open PMM Registers for write
    PMMCTL0_L |= PMMREGOFF;                 // and set PMMREGOFF
    __bis_SR_register(LPM3_bits | GIE);
    __no_operation();

    return 0;
}

void initGpio()
{
    P1DIR = 0xFF; P2DIR = 0xFF; P3DIR = 0xFF; P4DIR = 0xFF; P5DIR = 0xFF; P6DIR = 0xFF;
    P1REN = 0xFF; P2REN = 0xFF; P3REN = 0xFF; P4REN = 0xFF; P5REN = 0xFF; P6REN = 0xFF;
    P1OUT = 0x00; P2OUT = 0x00; P3OUT = 0x00; P4OUT = 0x00; P5OUT = 0x00; P6OUT = 0x00;

    // Disable the GPIO power-on default high-impedance mode
    // to activate previously configured port settings
    PM5CTL0 &= ~LOCKLPM5;
}

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = RTC_VECTOR
__interrupt void RTC_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(RTC_VECTOR))) RTC_ISR (void)
#else
#error Compiler not supported!
#endif
{
    switch(__even_in_range(RTCIV, RTCIV_RTCIF))
    {
        case RTCIV_NONE : break;            // No interrupt pending
        case RTCIV_RTCIF:                   // RTC Overflow
            // Toggle LED on P1.0
            P1OUT ^= BIT0;

            // Store P1OUT value in backup memory register
            *(unsigned int *)BKMEM_BASE = P1OUT;
            break;
        default:          break;
    }
}