SPI not working, ATmega328 only sending 1 byte

Question

I am trying to get SPI working on an ATmega328. This is my code:

#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#define ACK 0x7E
#define LONG_TIME 10000
//Initialize SPI Master Device
void spi_init_master (void)
{
 DDRB = (1<<PORTB5)|(1<<PORTB3); //Set MOSI, SCK as Output
 SPCR = (1<<SPE)|(1<<MSTR); //Enable SPI, Set as Master
}
//Function to send and receive data
unsigned char spi_tranceiver (unsigned char data)
{
 PORTC = 1<<PORTC2;
 PORTC = 0<<PORTC2;
 SPDR = data; //Load data into the buffer
 while(!(SPSR)&(1<<SPIF));
 return(SPDR); //Return received data
}
//Main
int main(void)
{
 DDRC= 0XFF; 
 spi_init_master();
 spi_tranceiver(6); 
 //spi_tranceiver(6);
 //spi_tranceiver(6); 
}

This is the output from the logic analyzer:

enter image description here

Notice those two comment lines. spi_tranceiver(6); If I remove those comments, I should get, from the logic analyzer:

• 3 times the amount of clock pulses for the blue layer.
• 3 times the amount of data sent, and;
• 3 times the amount of PORTC2 pules.

This is not the case. I get the below:

enter image description here

The device I am trying to SPI with isn't configured correctly. Does this matter?

Answer 1

It looks like you have the parantheses in the wrong spot while waiting for the SPI transaction to complete. Because the ! operator has a higher precedence than & it will be trying to do a bitwise not of the SPSR register first. Instead you want something like this:

while (!(SPSR & (1<<SPIF)))
 ;

At the moment presumably that wait is returning immediately so the SPDR register is getting set three times in rapid succession without enough time for the data to be transferred.

• dgamma3: many thanks! I have spent many many hours on this!
• whatsisname: Also, assuming that PORTC2 is the SS/CS line, that should be held low for the entirety of your SPI 'transaction', and should be taken out of your spi_tranceiver function and moved to somewhere surrounding that.