How to transfer data A1A2A3A4.. from internal memory of ATxmega128A1 via SPI master to slave form into two seperate DAC converters? - embedded

Question

I want to transfer data A1A2A3A4. From internal memory of ATxmega128A1 via SPI master to slave form into two seperate DAC converters such that DAC1 should have A1A3 and DAC2 with A2A4.
How can I write a code in AVR
// Transfer data from internal memory via SPI from Master to single Slave
if ( (SWITCHPORTL.IN & PIN2_bm) == 0 )
{
flip = false;
j = 0;
{
// Switch on LED 2
LEDPORT.OUTSET = PIN2_bm;
// Switch on LED 3
LEDPORT.OUTSET = PIN3_bm;
}
while (j < NUM_BYTES)
{
if (flip == false)
{
// Set slave select line low (active) for Port C
PORTC.OUTCLR = PIN4_bm;
}
// Give the data to the data register of the Master
SPIC.DATA = __far_mem_read(j+SDRAM_ADDR);
if (flip == true)
{
_delay_us(0.7); // wait for the 2nd 8-bit-block to be send -> delay 0.7us
// Set slave select line high (inactive)
PORTC.OUTSET = PIN4_bm;
_delay_us(1.9); // delay to adjust to sampling frequency 100 kHz -> 6.9us 200kHz -> 1.9us
}
flip = !flip;
j++;
}
}

Answer 1

Your general approach is right, but why do you not use SPIF flag of SPSR register? This will remove need of such precise _delay_us(0.7).
Also, looks like you forget to assert second chip select line.
So, general approach should be like following:
Read even byte (A1)
Assert slave select for first DAC.
Write data byte to SPIC.DATA
Loop while bit SPIF of SPSR == 0
Read from SPIC.DATA to clear SPIF bit.
Deassert slave select for first DAC
Read odd byte (A2)
Assert slave select for second DAC
Repeat steps 3-5
Repeat from beginning
Also, it is good idea to crate function that handles data write over SPI.