Interfacing HC-SR04 Ultrasonic Sensor to TM4C123 Tiv C

Two pieces of  program source code is presented below. The first piece of code  gives a highly precise result however requires the enabling of two General Purpose Timers; one for creating microseconds delay and the other for capturing the rising and falling edges of the Echo pin.

The second piece of code is more straightforward in understanding, however, less precise compared to the first. It requires enabling just one General Purpose Timer- for creating microseconds delays.

For more theoretical details about how the HC-Sr04 Ultrasonic Sensor works, please see the lesson Interfacing HC-SR04 Ultrasonic Sensor with Cortex-M.

//Author : cortex-m.com
//Tiltle :Interfacing HC-SR04 Ultrasonic sensor with Tiva C ARM Cortex-M4
#include "TM4C123.h"                    // Device header
#include <stdint.h>

void delay_Microsecond(uint32_t time);
void Timer0_init(void);
uint32_t measureD(void);

const double _16MHz_1clock = 62.5e-9; /*Value of 1clock cycle in nanoseconds*/
const uint32_t MULTIPLIER  = 5882;  /*Derived from speed of sound*/

#define ECHO (1U<<6) //PB6
#define TRIGGER(1U<<4) //PA4(OUTPUT)
#define BLUE_LED (1U<<2)//PF3 onboard Blue LED 
uint32_t highEdge,lowEdge;
uint32_t ddistance; /*Distance in centimeters*/ 
uint32_t counter =0; 
uint32_t measureD(void) { 
GPIOA->DATA &=~TRIGGER;
	delay_Microsecond(12);
	GPIOA->DATA |= TRIGGER;
	delay_Microsecond(12);
	GPIOA->DATA &=~TRIGGER;
	/*Capture firstEgde i.e. rising edge*/
	TIMER0->ICR =4;
	while((TIMER0->RIS & 4)==0){}; //Wait till captured
		highEdge =  TIMER0->TAR;

		/*Capture secondEdge i.e. falling edge */
		TIMER0->ICR =4; //clear timer capture flag
		while((TIMER0->RIS & 4)  ==0){};
			lowEdge = TIMER0->TAR;
			  ddistance = lowEdge -highEdge;
			  ddistance = _16MHz_1clock *(double) MULTIPLIER *(double)ddistance;

			return ddistance;

}
int main(void){
	SYSCTL->RCGCGPIO |=(1U<<0); //Enable clock for PORTA 
        SYSCTL->RCGCGPIO |=(1U<<5); //Enable clock for PORTF 
        GPIOA->DIR =TRIGGER;  
	GPIOF->DIR =BLUE_LED;
	GPIOA->DEN |=(ECHO)|(TRIGGER);
	GPIOF->DEN |= BLUE_LED;

	while(1){
		Timer0_init();
		 measureD();
    if(measureD() < 15) 
   GPIOF->DATA |=BLUE_LED;
   else
   GPIOF->DATA &=~BLUE_LED;
   delay_Microsecond(100);

  }
}
void delay_Microsecond(uint32_t time)
{
	int i;
	SYSCTL->RCGCTIMER |=(1U<<1); 
        TIMER1->CTL=0;
	TIMER1->CFG=0x04;
	TIMER1->TAMR=0x02;
	TIMER1->TAILR= 16-1;
	TIMER1->ICR =0x1;
	TIMER1->CTL |=0x01;

	for(i=0;i<time;i++){ 
       while((TIMER1->RIS & 0x1)==0);
		TIMER1->ICR = 0x1;
	}

}
void Timer0_init(void)
{
	SYSCTL->RCGCTIMER |=(1U<<0); 
        SYSCTL->RCGCGPIO |=(1U<<1); 
        GPIOB->DIR &=~ECHO;
	GPIOB->DEN |=ECHO;
	GPIOB->AFSEL |=ECHO;
	GPIOB->PCTL &=~0x0F000000;
	GPIOB->PCTL |= 0x07000000;

	TIMER0->CTL &=~1;
	TIMER0->CFG =4;
	TIMER0->TAMR = 0x17;
	TIMER0->CTL |=0x0C;
	TIMER0->CTL |=1;
}

//Author : cortex-m.com
//Program: Interfacing HC-SR04 with Tiva C ARM Cortex M4
//Remarks: Less precise version
#include "TM4C123.h"                    // Device header
#include <stdint.h>
#define MAX_TIME 7500
float measureD(void);
uint32_t counter =0;
float distance=0;
#define ECHO (1U<<2) //PA2(INput)
#define TRIGGER	(1U<<4) //PA4(OUTPUT)
#define BLUE_LED (1U<<2)//PF3 onboard Blue LED 
void delay_Microsecond(uint32_t time); 
float measureD(void){ 
        GPIOA->DATA &=~TRIGGER;
	delay_Microsecond(10);
	GPIOA->DATA |= TRIGGER;
	delay_Microsecond(10);
	GPIOA->DATA &=~TRIGGER;
	counter =0;
	while((GPIOA->DATA &ECHO)==0)	{}
	while(((GPIOA->DATA &ECHO )!=0) &(counter < MAX_TIME)) 
 { 
  counter++; 
  delay_Microsecond(1);
  } 
 distance = (float)counter*(float)0.0170000;
 return distance; } 
int main(void) 
    { 
   SYSCTL->RCGCGPIO |=(1U<<0); //Enable clock for PORTA 
   SYSCTL->RCGCGPIO |=(1U<<5); //Enable clock for PORTF 
   GPIOA->DIR =TRIGGER;
   GPIOF->DIR =BLUE_LED;
   GPIOA->DEN |=(ECHO)|(TRIGGER);
   GPIOF->DEN |= BLUE_LED;
while(1){

  measureD();   
    if(measureD() < 10.0){ 
     GPIOF->DATA |=BLUE_LED;
		}
	else{
	GPIOF->DATA &=~BLUE_LED;
	    }
	delay_Microsecond(10);
  }
}

void delay_Microsecond(uint32_t time)
{
	int i;
	SYSCTL->RCGCTIMER |=(1U<<1); 
        TIMER1->CTL=0;
	TIMER1->CFG=0x04;
	TIMER1->TAMR=0x02;
	TIMER1->TAILR= 16-1;
	TIMER1->ICR =0x1;
	TIMER1->CTL |=0x01;

	for(i=0;i<time;i++){ 
        while((TIMER1->RIS & 0x1)==0);
		TIMER1->ICR = 0x1;
	}

}

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