#include <avr/io.h>
#include <stdint.h>
#include <math.h>


#include <spi.h>


void spi_init(){
	uint8_t spcr, spsr, d;

	/* calculate clock divisor,
	 * gcc with optimize will do that calculation compile-time. */
	uint8_t spi_clock_divisor(){
		double d; 
		d = F_CPU / SPI_BAUDRATE;
		d = ceil((log(d)/log(2))*0.95); // clock needs dividing by 2^d
										// the 0.95 to avoid ceil issues
		return d-1;  // the -1 because minimum divisor is /2
	}

	d = spi_clock_divisor();
	if(d>7){
#warning "spi baudrate too slow, cannot be set"
		d=7;
	}

	spsr = 0;
	spsr |=	(d & 1) ? 0 : _BV(SPI2X);
	spcr = 0 | _BV(SPIE) | _BV(SPE);
	spcr |= (d & 2) ? _BV(SPR0) : 0;
	spcr |= (d & 4) ? _BV(SPR1) : 0;

#ifdef SPI_MASTER
	spcr |= _BV(MSTR);
#endif		

	SPCR = spcr;
	SPSR = spsr;
}