Read SRF04 with STM32F4 discovery

#include "stm32f4xx_conf.h"
#include "math.h"
#include "stdio.h"
#include "stdlib.h"

#define crystal   168

#define ECHO  GPIO_ReadInputDataBit(GPIOA,GPIO_Pin_15)
#define TRIGER_SET GPIO_WriteBit(GPIOA, GPIO_Pin_14, 1)
#define TRIGER_RESET GPIO_WriteBit(GPIOA, GPIO_Pin_14, 0)

unsigned int count=0;
unsigned char jrk;
unsigned char jrk_dpn;
unsigned char kata1[16];
unsigned char kata2[16];

void delay_ms(unsigned int waktu)
{
  unsigned int a, b, c;
  c=(float)crystal*45.4876273654;
  for(a=0;a<waktu;a++)
  {
 for(b=0;b<c;b++);
  }
}

void delay_us(unsigned int waktu)
{
unsigned int a, b;
b=(float)crystal*0.03472222222222222;
waktu=(float)waktu*b;
for(a=0;a<waktu;a++)
{
for(b=0;b<crystal;b++);
}
}



void inisialisasi_GPIO()
{
GPIO_InitTypeDef definisi_GPIO;

definisi_GPIO.GPIO_Pin = GPIO_Pin_14;
definisi_GPIO.GPIO_Mode = GPIO_Mode_OUT;
definisi_GPIO.GPIO_OType = GPIO_OType_PP;
definisi_GPIO.GPIO_PuPd = GPIO_PuPd_NOPULL;
definisi_GPIO.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &definisi_GPIO);

definisi_GPIO.GPIO_Pin = GPIO_Pin_15;
definisi_GPIO.GPIO_Mode = GPIO_Mode_IN;
definisi_GPIO.GPIO_PuPd = GPIO_PuPd_UP;
definisi_GPIO.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &definisi_GPIO);
}

unsigned char baca_srf04()
 {
  count=0;
  //pemberian pemicu berupa pulsa positif minimal 10us utk aktivasi sensor
  TRIGER_SET;
  delay_ms(10);
  TRIGER_RESET;
  //menunggu hingga ECHO = 1
  while(ECHO==0){};
  //mencacah untuk mengukur waktu lamanya pulsa 1 dari ECHO
  while(ECHO==1)
  {
 count++;
  };
 //mengkonversikan hasil cacahan menjadi jarak dalam cm
  jrk=count*10/232;
  return jrk;
}
int srf=0;
int main(void)
{
SystemInit();

RCC_APB2PeriphClockCmd(RCC_APB2Periph_SYSCFG, ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,  ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB,  ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC,  ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD,  ENABLE);
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOE,  ENABLE);


inisialisasi_GPIO();


while (1)
     {
      srf=baca_srf04();

     }
}