/* SPI code for interfacing w/ SPI Real Time Clock chip

	Pin Description
	1 - X1 - 32.768 kHz crystal input
	2 - X2 - crystal output
	3 - ~RST - reset Output - NC - low if RSTIN1 or RSTIN2 is low, if VCC falls below Vpfd
	4 - WDI - watchdog input - NC
	5 - ~RSTIN1 - reset input one (active low) - NC
	6 - ~RSTIN2 - reset input two (active low) - NC
	7 - VBAT - battery voltage - ~3V, battery GND common w/ VSS
	8 - VSS - hook up to GND
	9 - SDO - Serial Data Output (hooked up to B6 - MISO)
 10 - SCL - Serial CLK (hooked up to B7 - SCK) - Max = 2 MHz
 11 - SQW - Square Wave Output - NC
 12 - SDI - Serial Data Input (hooked up to B5 - MOSI)
 13 - TH - Power Off threshold select - set to GND
 14 - NC
 15 - ~E - Chip Enable (active low) - Hook up to B4
 16 - VCC - 5V
 
 Notes - When VCC falls below Vpfd (power failure detect), E becomes disabled & high impedance
 resulting in severed communication until VCC restored.  Power is switched over to battery at this
 time and clock will continue to increment.
 E remains disabled for ~0.1 s after VCC restored - need to wait some time before reads & writes can be made
 
*/

#include "spi_rtc.h"


//returns read result from a specified RTC register
unsigned char spi_read_reg (unsigned char reg){
  
  unsigned char read; //temp variable for storing spi read
	
  PORTB.4=0;
  spi(reg);
  read = spi(0x00);
  PORTB.4=1;
  return read;
  
}    

//writes byte to specified RTC register
void spi_write_reg (unsigned char reg, unsigned char data){
  
  PORTB.4=0;
  spi((0x80 | reg));
  spi(data);
  PORTB.4=1;
  
}


//Initialize the RTC
void spi_init(void){
	
	unsigned char temp;
	
	// Set SPI CTRL & Status reg
	SPCR=0b01011101;		//MCU is master, SPI enabled, MSB first, SCK = 1 MHz
	SPSR=0x00;				//2xCK = off
	
	PORTB.4=1;	//Chip Disabled 
	PORTB.5=1;
	PORTB.6=1;
	PORTB.7=1;
	
	         
	while((spi_read_reg(0x02)==0xFF));  //while E is high resistance
	 
	spi_write_reg(0x0C,0x00);           //Turn off HT bit
	
	temp = spi_read_reg(0x01);          //Read seconds reg
	spi_write_reg(0x01,(temp & 0x7F));  //Turn off ST bit
	     
}