sd_routines.c

#include "sd.h"

//+==========================================+
//| initialization of the sd-card			 |
//+==========================================+
char SD_init()
{
	DDRSP &=~ (1<<SPI_MISO);					// sets pin MISO to an input
	DDRSP |=  (1<<SPI_MOSI);					// sets pin MOSI to an output
	DDRSP |=  (1<<SPI_SS);						// sets pin SS to an output
	DDRSP |=  (1<<SPI_SCK);						// sets pin SCK to an output

	unsigned char timeout = 0;
	
	for (unsigned int a = 0; a < 550; a++)		// wastes some cycles, waits for stabilisation of the power source
	{
		nop();									// no operation
	}
	
	volatile char IOReg;
	SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0)|(1<<SPR1);
	// SPE 			- enables SPI-mode
	// MSTR 		- sets µC to be the master
	// SPR0, SPR0 	- setting the SPI-clock
	
	SPSR = (0<<SPI2X);
	// SPI2X		- setting the SPI-clock(SCK) to (µC-clock/128)
	
	IOReg = SPSR;                 				// clear SPIF bit in SPSR
    IOReg = SPDR;

	for (unsigned char i = 0; i < 0x0F; i++)	// sends 74+ clocks to the sd-card
	{
		SD_WRbyte(0xFF);
	}

	// load CMD with command CMD0 = GO_IDLE_STATE
	char CMD[] = {0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x95};
	while(SD_WRcmd(CMD) != 1)					// repeat until sd-card sends 0x01
	{
		if(timeout++ > 300)
		{
			SD_disable();
			return(1);
		}
		timeout = 0;
	}
	
	// load CMD with command CMD55 = prefix for an ACMD-command
	CMD[0] = 0x77;
	CMD[7] = 0x01;
	while(SD_WRcmd(CMD) != 1)
	{
		if(timeout++ > 300)
		{
			SD_disable();
			return(1);
		}
		timeout = 0;
	}
	
	// load CMD with command ACMD41 = SD_SEND_OP_COND
	CMD[0] = 0x69;
	while(SD_WRcmd(CMD) != 0)
	{
		if(timeout++ > 300)
		{
			SD_disable();
			return(1);
		}
		timeout = 0;
	}
	
	return(0);
}

//+==========================================+
//| sends one byte to the sd-card			 |
//+==========================================+
void SD_WRbyte (char byte)
{
	SPDR = byte;						// load byte in the SPDR, data-transfer begins
	while(!(SPSR & (1<<SPIF)))			// SPIF = 1 when transfer completed
	{
	}
}

//+==========================================+
//| receives one byte from the sd-card		 |
//+==========================================+
char SD_RDbyte ()
{
	SPDR = 0xFF;
	while(!(SPSR & (1<<SPIF)))
	{
	}
	return(SPDR);
}

//+==========================================+
//| sends a command to the sd-card			 |
//+==========================================+
char SD_WRcmd (char *cmd)
{
	unsigned char timeout = 0;
	char temp = 0xFF;
	SD_enable();
	
	for ( unsigned char i = 0; i < 0x06; i++)
	{
		SD_WRbyte(*cmd++);
	}

	while(temp == 0xFF)
	{
		temp = SD_RDbyte();
		if(timeout++ > 400)
		{
			break;
		}
	}
	
	SD_disable();						// deactivates SD-card
	SD_WRbyte(0xFF);					// wastes eight cycles
	
	return(temp);
}

//+==========================================+
//| enables the sd-card						 |
//+==========================================+
void SD_disable ()
{
	DDRSP |= (1<<SPI_SS);
}

//+==========================================+
//| disables the sd-card					 |
//+==========================================+
void SD_enable ()
{
	DDRSP &=~(1<<SPI_SS);

}