#include "ul.h"

#include "intrins.h"
sbit Tx = P1 ^ 0;
sbit Rx = P1 ^ 1;
void Delay12us(void)  //@12.000MHz
{
  unsigned char data i;

  _nop_();
  _nop_();
  i = 33;  // 38
  while (--i);
}
void Ut_Wave_Init() {
  unsigned char i;
  for (i = 0; i < 8; i++) {
    Tx = 1;
    Delay12us();
    Tx = 0;
    Delay12us();
  }
}
unsigned char Ut_Wave_Data() {
  unsigned int time;
  CH = CL = 0;
  CMOD = 0x00;

  EA = 0;
  Ut_Wave_Init();
  EA = 1;

  CR = 1;
  while (Rx && !CF);
  CR = 0;
  if (!CF) {  // us -> s 10^(-6)
    // m -> cm 10^2
    //  10^(-4)
    // L = V*T/2=340*time/2=170*10^(-4)*time=0.017*time
    time = CH << 8 | CL;
    return (0.017 * time + 3);
  } else {
    CF = 0;
    return 0;
  }
}