void spi_reset();
char spi_read(char);
char spi_read_rx_buffer (char, char);
void spi_write(char, char);
void spi_load_tx_buffer(char, char, char, char);
void spi_RTS(char, char, char);
char spi_read_status();
char spi_rx_status();
void spi_bit_modify(char, char, char);


// resete the CAN controller
void spi_reset()
{
  	PORTB.4 = 0;
  
  	SPDR = 0b11000000;
  	while(SPSR.7 == 0) { }
     
     // clear SPIF flag            
     SPSR.7 = 0;
  	
  	PORTB.4 = 1;
  
}


// read a register on the controller
char spi_read(char addr)
{
  	unsigned char data;
  
  	// set chip select low
  	SPCR = 0b01010000;
  	PORTB.4 = 0;

  	SPDR = 0b00000011;
  	while (SPSR.7 == 0) { }
  
  	SPDR = addr;
  	while (SPSR.7 == 0) { }
  
  	SPDR = 0x00;
  	while (SPSR.7 == 0) { }
  
  	data = SPDR;
              
  	// set chip select high
  	PORTB.4 = 1;
  
  	return data;

}

// read from an rx buffer register
char spi_read_rx_buffer (char n, char m)
{
  	// n and m each are a single bit, 1 or 0


  	unsigned char cmd, data;
  	cmd = 0b10010000 | (n<<2) | (m<<1);
        SPCR = 0b01010000;
  	PORTB.4 = 0;
  
  	SPDR = cmd;
  	while (SPSR.7 == 0) { }
  
  	SPDR = 0x00;
  	while (SPSR.7 == 0) { }
  
  	data = SPDR;
  
  	PORTB.4 = 1;
  
  	return data;
  
}

// write to a register
void spi_write(char addr, char data)
{
        SPCR = 0b01010000;
	PORTB.4 = 0;
  
	SPDR = 0b00000010;
	while (SPSR.7 == 0) { }
  
	SPDR = addr;
	while (SPSR.7 == 0) { } 
  
  	SPDR = data;
  	while (SPSR.7 == 0) { }

  	// clear SPIF flag  
  	SPSR.7 = 0;                   
  
  	PORTB.4 = 1;
  
}
  
// write to a tx buffer register
void spi_load_tx_buffer(char a, char b, char c, char data)
{
     // a,b,c, are each 1 bit
     
     unsigned char cmd;
     SPCR = 0b01010000;
     cmd = 0b01000000 | (a<<2) | (b<<1) | c; 
     
     PORTB.4 = 0;
     
     SPDR = cmd;
     while (SPSR.7 == 0) { }
     
     SPDR = data;
     while (SPSR.7 == 0) { }
     
     SPSR.7 = 0;
     
     PORTB.4 = 1;
     
}
                 
// send request-to-send command (initiate transmission)
void spi_RTS(char two, char one, char zero)
{
	// two, one, zero are each 1 bit
	
	unsigned char cmd;
	SPCR = 0b01010000;
	cmd = 0b10000000 | (two<<2) | (one<<1) | zero;
	
	PORTB.4 = 0;
	
	SPDR = cmd;
	while (SPSR.7 == 0) { }
	
	SPSR.7 = 0;
	
	PORTB.4 = 1;

}

// read status bits from the controller
char spi_read_status()
{
     
	unsigned char data;
	SPCR = 0b01010000;
	PORTB.4 = 0;
	
	SPDR = 0b10100000;
	while (SPSR.7 == 0) { }
	
	SPDR = 0x00;
	while (SPSR.7 == 0) { }
	
	SPDR = 0x00;
	while (SPSR.7 == 0) { }
	
	data = SPDR;
	
	PORTB.4 = 1;
	
	return data;
	
}

// read the rx status bits
char spi_rx_status()
{

 	unsigned char data;
	SPCR = 0b01010000;
	PORTB.4 = 0;
	
	SPDR = 0b10110000;
	while (SPSR.7 == 0) { }
	
	SPDR = 0x00;
	while (SPSR.7 == 0) { }
	
	SPDR = 0x00;
	while (SPSR.7 == 0) { }
	
	data = SPDR;
	
	PORTB.4 = 1;
	
	return data;	

}

// modify one or several bits in a register
void spi_bit_modify(char addr, char mask, char data)
{
        SPCR = 0b01010000;
	PORTB.4 = 0;     
	
	SPDR = 0b00000101;
	while (SPSR.7 == 0) { }
	
	SPDR = addr;
	while (SPSR.7 == 0) { }
	
	SPDR = mask;
	while (SPSR.7 == 0) { }
	
	SPDR = data;
	while (SPSR.7 == 0) { }
	
	SPSR.7 = 0;
	
	PORTB.4 = 1;
	
}