period.c

// PeriodEFM8.c: Measure the period of a signal on pin P0.1.
//
// By:  Jesus Calvino-Fraga (c) 2008-2018
//
// The next line clears the "C51 command line options:" field when compiling with CrossIDE
//  ~C51~  

#include <EFM8LB1.h>
#include <stdio.h>

#define SYSCLK      72000000L  // SYSCLK frequency in Hz
#define BAUDRATE      115200L  // Baud rate of UART in bps

unsigned char overflow_count;

char _c51_external_startup (void)
{
	// Disable Watchdog with key sequence
	SFRPAGE = 0x00;
	WDTCN = 0xDE; //First key
	WDTCN = 0xAD; //Second key
  
	VDM0CN |= 0x80;
	RSTSRC = 0x02;

	#if (SYSCLK == 48000000L)	
		SFRPAGE = 0x10;
		PFE0CN  = 0x10; // SYSCLK < 50 MHz.
		SFRPAGE = 0x00;
	#elif (SYSCLK == 72000000L)
		SFRPAGE = 0x10;
		PFE0CN  = 0x20; // SYSCLK < 75 MHz.
		SFRPAGE = 0x00;
	#endif
	
	#if (SYSCLK == 12250000L)
		CLKSEL = 0x10;
		CLKSEL = 0x10;
		while ((CLKSEL & 0x80) == 0);
	#elif (SYSCLK == 24500000L)
		CLKSEL = 0x00;
		CLKSEL = 0x00;
		while ((CLKSEL & 0x80) == 0);
	#elif (SYSCLK == 48000000L)	
		// Before setting clock to 48 MHz, must transition to 24.5 MHz first
		CLKSEL = 0x00;
		CLKSEL = 0x00;
		while ((CLKSEL & 0x80) == 0);
		CLKSEL = 0x07;
		CLKSEL = 0x07;
		while ((CLKSEL & 0x80) == 0);
	#elif (SYSCLK == 72000000L)
		// Before setting clock to 72 MHz, must transition to 24.5 MHz first
		CLKSEL = 0x00;
		CLKSEL = 0x00;
		while ((CLKSEL & 0x80) == 0);
		CLKSEL = 0x03;
		CLKSEL = 0x03;
		while ((CLKSEL & 0x80) == 0);
	#else
		#error SYSCLK must be either 12250000L, 24500000L, 48000000L, or 72000000L
	#endif
	
	P0MDOUT |= 0x10; // Enable UART0 TX as push-pull output
	XBR0     = 0x01; // Enable UART0 on P0.4(TX) and P0.5(RX)                     
	XBR1     = 0X00;
	XBR2     = 0x40; // Enable crossbar and weak pull-ups

	#if (((SYSCLK/BAUDRATE)/(2L*12L))>0xFFL)
		#error Timer 0 reload value is incorrect because (SYSCLK/BAUDRATE)/(2L*12L) > 0xFF
	#endif
	// Configure Uart 0
	SCON0 = 0x10;
	CKCON0 |= 0b_0000_0000 ; // Timer 1 uses the system clock divided by 12.
	TH1 = 0x100-((SYSCLK/BAUDRATE)/(2L*12L));
	TL1 = TH1;      // Init Timer1
	TMOD &= ~0xf0;  // TMOD: timer 1 in 8-bit auto-reload
	TMOD |=  0x20;                       
	TR1 = 1; // START Timer1
	TI = 1;  // Indicate TX0 ready
	
	return 0;
}

// Uses Timer3 to delay <us> micro-seconds. 
void Timer3us(unsigned char us)
{
	unsigned char i;               // usec counter
	
	// The input for Timer 3 is selected as SYSCLK by setting T3ML (bit 6) of CKCON0:
	CKCON0|=0b_0100_0000;
	
	TMR3RL = (-(SYSCLK)/1000000L); // Set Timer3 to overflow in 1us.
	TMR3 = TMR3RL;                 // Initialize Timer3 for first overflow
	
	TMR3CN0 = 0x04;                 // Sart Timer3 and clear overflow flag
	for (i = 0; i < us; i++)       // Count <us> overflows
	{
		while (!(TMR3CN0 & 0x80));  // Wait for overflow
		TMR3CN0 &= ~(0x80);         // Clear overflow indicator
	}
	TMR3CN0 = 0 ;                   // Stop Timer3 and clear overflow flag
}

void waitms (unsigned int ms)
{
	unsigned int j;
	for(j=ms; j!=0; j--)
	{
		Timer3us(249);
		Timer3us(249);
		Timer3us(249);
		Timer3us(250);
	}
}

void TIMER0_Init(void)
{
	TMOD&=0b_1111_0000; // Set the bits of Timer/Counter 0 to zero
	TMOD|=0b_0000_0001; // Timer/Counter 0 used as a 16-bit timer
	TR0=0; // Stop Timer/Counter 0
}

void main (void) 
{
	float period;
	
	TIMER0_Init();

	waitms(500); // Give PuTTY a chance to start.
	printf("\x1b[2J"); // Clear screen using ANSI escape sequence.

	printf ("EFM8 Period measurement at pin P0.1 using Timer 0.\n"
	        "File: %s\n"
	        "Compiled: %s, %s\n\n",
	        __FILE__, __DATE__, __TIME__);

    while (1)
    {
    	// Reset the counter
		TL0=0; 
		TH0=0;
		TF0=0;
		overflow_count=0;
		
		while(P0_1!=0); // Wait for the signal to be zero
		while(P0_1!=1); // Wait for the signal to be one
		TR0=1; // Start the timer
		while(P0_1!=0) // Wait for the signal to be zero
		{
			if(TF0==1) // Did the 16-bit timer overflow?
			{
				TF0=0;
				overflow_count++;
			}
		}
		while(P0_1!=1) // Wait for the signal to be one
		{
			if(TF0==1) // Did the 16-bit timer overflow?
			{
				TF0=0;
				overflow_count++;
			}
		}
		TR0=0; // Stop timer 0, the 24-bit number [overflow_count-TH0-TL0] has the period!
		period=(overflow_count*65536.0+TH0*256.0+TL0)*(12.0/SYSCLK);
		// Send the period to the serial port
		printf( "\rT=%f ms    ", period*1000.0);
		
    }
	
}