SPI Psuedo Code

Enable the clock to Port A
Enable the clock to SSI module, Here R0, R1, R2, R3 are Module 0,1,2,3
Use SSI module 0
Wait for the GPIO port to be ready

Program the GPIO to use the alternate function on the SSI pins 
Set the mux position in GPIOPCTL to select the SSI use of the pins

2 is the mux value to select SSI1Rx, SSI1Tx
    
Set PA2 to SSI0Clk
Set PA3 to SSI0Fss		
Set PA4 to SSI0Rx
Set PA5 to SSI0Tx
 
Program the port lines for digital I/O
Set PA4 Input
Set PA2 Output
Set PA3 Output
Set PA5 Output

Wait for the SSI1 to be ready
Make sure the the SSI is disabled before programming mode bits
Select master mode (MS) & TXRIS indicating End of Transmit (EOT)
Configure the SSI clock source to the system clock
Configure the clock pre-scaler 
Configure clock rate (SCR), phase & polarity (SPH=1, SPO=1), mode (FRF=0), data size (DSS=8 bits)
Locally enable interrupts on TXRIS
NVIC Interrupt number
Globally enable
Make sure that the SSI is enabled for operation



Function Transmit(signal)
{
Give the signal to the command generator
}

Function TransmitIntResponse(){
   Start by clearing the source of the interrupt
   Get the signal from Command generator
    
}