基于MSP430F5529的超声波测距源码，自己写的可能不对，仅供参考

超声波测距的原理大家Google一下就应该知道了，因此基于MSP430的超声波主要是调整时钟就行了。

代码如下：

#include "msp430f5529.h"
#include "usart.h"
#include "stdio.h"
 
double a = 1.111;       //距离
long long next;         //寄存器值
/*
 * P3.6与TB0.6相连接，输出信号
 */
int tim = 0;        //溢出次数
 
void SetVcoreUp (unsigned int level)
{
  PMMCTL0_H = PMMPW_H;
  SVSMHCTL = SVSHE + SVSHRVL0 * level + SVMHE + SVSMHRRL0 * level;
  SVSMLCTL = SVSLE + SVMLE + SVSMLRRL0 * level;
  while ((PMMIFG & SVSMLDLYIFG) == 0);
  PMMIFG &= ~(SVMLVLRIFG + SVMLIFG);
  PMMCTL0_L = PMMCOREV0 * level;
  if ((PMMIFG & SVMLIFG))
    while ((PMMIFG & SVMLVLRIFG) == 0);
  SVSMLCTL = SVSLE + SVSLRVL0 * level + SVMLE + SVSMLRRL0 * level;
  PMMCTL0_H = 0x00;
}
 
void set(void)
{
  volatile unsigned int i;
  WDTCTL = WDTPW+WDTHOLD;                   // Stop WDT
  P1DIR |= BIT1;                            // P1.1 output
  P1DIR |= BIT0;                            // ACLK set out to pins
  P1SEL |= BIT0;
  P2DIR |= BIT2;                            // SMCLK set out to pins
  P2SEL |= BIT2;
  P7DIR |= BIT7;                            // MCLK set out to pins
  P7SEL |= BIT7;
  // Increase Vcore setting to level3 to support fsystem=25MHz
  // NOTE: Change core voltage one level at a time..
  SetVcoreUp (0x01);
  SetVcoreUp (0x02);
  SetVcoreUp (0x03);
  UCSCTL3 = SELREF_2;                       // Set DCO FLL reference = REFO
  UCSCTL4 |= SELA_2;                        // Set ACLK = REFO
  __bis_SR_register(SCG0);                  // Disable the FLL control loop
  UCSCTL0 = 0x0000;                         // Set lowest possible DCOx, MODx
  UCSCTL1 = DCORSEL_7;                      // Select DCO range 50MHz operation
  UCSCTL2 = FLLD_0 + 762;                   // Set DCO Multiplier for 25MHz
  __bic_SR_register(SCG0);                  // Enable the FLL control loop
 
  __delay_cycles(782000);
  do
  {
    UCSCTL7 &= ~(XT2OFFG + XT1LFOFFG + DCOFFG);
                                            // Clear XT2,XT1,DCO fault flags
    SFRIFG1 &= ~OFIFG;                      // Clear fault flags
  }while (SFRIFG1&OFIFG);                   // Test oscillator fault flag
  P6DIR |= BIT0;
 
}
 
void main()
{
    set();
    WDTCTL = WDTPW+WDTHOLD;                   // Stop WDT
    UART_Init();                //串口初始化
 
    P3DIR |= BIT6;        
    P3OUT &=~ BIT6;     
 
    P3DIR &=~ BIT5;      
    P3IN &=~ BIT5;       
 
    P2DIR |= 0X00;   
    P2IFG = 0X00;  
    P2IE = BIT0;    
    P2IES = BIT0;  
    P2IN = BIT0;  
    P2OUT = BIT0;    
    P2REN = BIT0;   
 
    __enable_interrupt();     
 
    P1SEL |= BIT4;    
    P1DIR |= BIT4;    
    P1DS |= BIT4;   
    P1OUT &=~ BIT4;   
 
    while(1)
    {
        P3OUT = BIT6;  
        __delay_cycles(4);
        P3OUT &=~ BIT6;
        P2OUT &=~ BIT0;
        __delay_cycles(40000);
    }
}
 
 
#pragma vector=PORT2_VECTOR  
 
__interrupt void Port2_ISR(void)
{
 
    unsigned int temp;   
    if((P2IN&0X01)!=0X01)
    {
        temp=P2IFG;     
        P2IFG=0x00; 
        if(temp==0x01)
        {
            P2OUT = BIT0;  
            //开始计时
            TA0CCTL0 = CCIE;
            TA0CCR0 = 20000;
            TA0CTL = TASSEL_2 + MC_1 + TACLR;      
            __bis_SR_register(GIE);
            while((P3IN&0X20) == 0X20);
            //a + TA0R
            TA0CTL = MC0;
            //next = TA0R;
 
            printf("next = %ld\n",TA0R);
 
        }
    }
}
 
#pragma vector = TIMER0_A0_VECTOR
__interrupt void TIMER0_A0_ISR(void)
{
    tim++;
    if(a>10)
    {
        tim = 0;
        P3OUT = BIT6;  
        __delay_cycles(4); 
        P3OUT &=~ BIT6;
    }
 
}