I was having some issues trying to communicate with DS1306. I managed to get the communication working (am able to both read and write), but there's still something that's puzzled me. Below is the code. In the ioinit() method, I set the SPI port to master and enable it. Then in the beginning of the main function (should be executed right after ioinit), I have to read the SPCR register and reinit the SPCR register. If I remove either of these lines, it will hang on the first SPI transaction. Any idea why those extra lines are needed? Or is there something else or a cleaner way I should be doing the init?
static void ioinit(void)
{
// Set SPI port to master, sample on falling edge and enable it
SPCR = (1<<SPE)|(1<<MSTR)|(1<<CPHA);
// Set SCK, CS, MOSI and RTC_CS as output
DDRB = (1<<RTC_SDO) | (1<<RTC_SCK) | (1<<RTC_CS) | (1<<PORT2);
// Set CS high to avoid problems with SPI slave mode
PORTB |= _BV(PORT2);
// Set RTC_CS low to de-select DS1306
RTC_PO &= ~_BV(RTC_CS);
}
int main(void)
{
ioinit();
// WHY ARE THESE LINES REQUIRED???
char clear;
clear = SPCR;
SPCR = (1<<SPE)|(1<<MSTR)|(1<<CPHA);
// WHY ARE THESE LINES REQUIRED???
while ( 1 )
{
char secs = ReadRTC( 0x00 );
fprintf( stderr, "Secs: %x\n", secs );
_delay_ms(30);
}
return 0;
}
char SPITransfer( char aDat )
{
SPDR = aDat;
while ( ! (SPSR & (1<<SPIF)) ) {};
return SPDR;
}
void WriteRTC( char aReg, char aDat )
{
RTCTransfer( aReg, aDat );
}
char ReadRTC( char aReg )
{
return RTCTransfer( aReg, 0 );
}
char RTCTransfer( char aReg, char aDat )
{
char spiByte;
// Clear SPIE bit if set
spiByte = SPSR;
spiByte = SPDR;
// Set CS to high to enable DS1306
RTC_PO |= _BV(RTC_CS);
// Send register, then send/read data
SPITransfer( aReg );
spiByte = SPITransfer( aDat );
// Set CS to low to disable DS1306
RTC_PO &= ~_BV(RTC_CS);
return spiByte;
}
