Problem with the ADS1234-Tiva C conversion while loop

//*****************************************************************************

#include <stdbool.h>
#include <stdint.h>
#include "inc/hw_memmap.h"
#include "driverlib/gpio.h"
#include "driverlib/pin_map.h"
#include "driverlib/ssi.h"
#include "driverlib/sysctl.h"
#include "driverlib/uart.h"
#include "utils/uartstdio.h"

//*****************************************************************************
// Number of bytes to send and receive.
//
#define NUM_SSI_DATA            3

//*****************************************************************************
// This function sets up UART0 to be used for a console to display conversion
//
void InitConsole(void)
{
    // Enable GPIO port A which is used for UART0 pins.
   SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);

    //
    // Configure the pin muxing for UART0 functions on port A0 and A1.
    GPIOPinConfigure(GPIO_PA0_U0RX);
    GPIOPinConfigure(GPIO_PA1_U0TX);

    //
    // Enable UART0 so that we can configure the clock.
    SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);

    // Use the internal 16MHz oscillator as the UART clock source.
    //
    UARTClockSourceSet(UART0_BASE, UART_CLOCK_PIOSC);

    // Select the alternate (UART) function for these pins.
    GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);

    // Initialize the UART for console I/O.
    UARTStdioConfig(0, 115200, 16000000);
}

//*****************************************************************************
//
// Configure SSI0 in master Freescale (SPI) mode.  This example will send out
// 3 bytes of data, then wait for 3 bytes of data to come in.  This will all be
// done using the polling method.
//
//*****************************************************************************
int
main(void)
{
    uint32_t pui32DataTx[NUM_SSI_DATA];
    uint32_t pui32DataRx[NUM_SSI_DATA];
    uint32_t ui32Index;
    double lettura = 0;

    //
    // Set the clocking to run directly from the external crystal/oscillator.
    SysCtlClockSet(SYSCTL_SYSDIV_2 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);

    //
    // Set up the serial console to use for displaying messages.  This is
    // just for this example program and is not needed for SSI operation.
    //
    InitConsole();

    //
    // Display the setup on the console.
    //
    UARTprintf("SSI ->\n");
    UARTprintf("  Mode: SPI\n");
    UARTprintf("  Data: 8-bit\n\n");

    //
    // The SSI0 peripheral must be enabled for use.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI0);

    //
    // For this example SSI0 is used with PortA[5:2].  The actual port and pins
    // used may be different on your part, consult the data sheet for more
    // information.  GPIO port A needs to be enabled so these pins can be used.
    // TODO: change this to whichever GPIO port you are using.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);

    //
    // Configure the pin muxing for SSI0 functions on port A2, A3, A4, and A5.
    // This step is not necessary if your part does not support pin muxing.
    // TODO: change this to select the port/pin you are using.
    //
    GPIOPinConfigure(GPIO_PA2_SSI0CLK);
    GPIOPinConfigure(GPIO_PA3_SSI0FSS);
    GPIOPinConfigure(GPIO_PA4_SSI0RX);
    GPIOPinConfigure(GPIO_PA5_SSI0TX);

    //
    // Configure the GPIO settings for the SSI pins.  This function also gives
    // control of these pins to the SSI hardware.  Consult the data sheet to
    // see which functions are allocated per pin.
    // The pins are assigned as follows:
    //      PA5 - SSI0Tx
    //      PA4 - SSI0Rx
    //      PA3 - SSI0Fss
    //      PA2 - SSI0CLK
    // TODO: change this to select the port/pin you are using.
    //
    GPIOPinTypeSSI(GPIO_PORTA_BASE, GPIO_PIN_5 | GPIO_PIN_4 | GPIO_PIN_3 | GPIO_PIN_2);

    //
    // Configure and enable the SSI port for SPI master mode.  Use SSI0,
    // system clock supply, idle clock level low and active low clock in
    // freescale SPI mode, master mode, 1MHz SSI frequency, and 8-bit data.
    // For SPI mode, you can set the polarity of the SSI clock when the SSI
    // unit is idle.  You can also configure what clock edge you want to
    // capture data on.  Please reference the datasheet for more information on
    // the different SPI modes.
    //
    SSIConfigSetExpClk(SSI0_BASE, SysCtlClockGet(), SSI_FRF_MOTO_MODE_1, SSI_MODE_MASTER, 5000000, 8);

    //
    // Enable the SSI0 module.
    //
    SSIEnable(SSI0_BASE);

    // Read any residual data from the SSI port.  This makes sure the receive
    // FIFOs are empty, so we don't read any unwanted junk.  This is done here
    // because the SPI SSI mode is full-duplex, which allows you to send and
    // receive at the same time.  The SSIDataGetNonBlocking function returns
    // "true" when data was returned, and "false" when no data was returned.
    // The "non-blocking" function checks if there is any data in the receive
    // FIFO and does not "hang" if there isn't.
    //
    while (1)
    {


    while(SSIDataGetNonBlocking(SSI0_BASE, &pui32DataRx[0]))
    {
    }

    // Initialize the data to send.
    //
    pui32DataTx[0] = 0;
    pui32DataTx[1] = 0;
    pui32DataTx[2] = 0;

    // Display indication that the SSI is transmitting data.
    //
    UARTprintf("Sent:\n  ");

    //
    // Send 3 bytes of data.
    //
    for(ui32Index = 0; ui32Index < NUM_SSI_DATA; ui32Index++)
    {
        //
        // Display the data that SSI is transferring.
        //
        UARTprintf("'%c' ", pui32DataTx[ui32Index]);

        //
        // Send the data using the "blocking" put function.  This function
        // will wait until there is room in the send FIFO before returning.
        // This allows you to assure that all the data you send makes it into
        // the send FIFO.
        //
        SSIDataPut(SSI0_BASE, pui32DataTx[ui32Index]);
    }

    //
    // Wait until SSI0 is done transferring all the data in the transmit FIFO.
    //
    while(SSIBusy(SSI0_BASE))
    {
    }

    //
    // Display indication that the SSI is receiving data.
    //
    UARTprintf("\nReceived:\n  ");

    //
    // Receive 3 bytes of data.
    //
    for(ui32Index = 0; ui32Index < NUM_SSI_DATA; ui32Index++)
    {
        //
        // Receive the data using the "blocking" Get function. This function
        // will wait until there is data in the receive FIFO before returning.
        //
    	if (ui32Index == 0)
    	{
        SSIDataGet(SSI0_BASE, &pui32DataRx[0]);

        // Since we are using 8-bit data, mask off the MSB.
        //
        pui32DataRx[0] &= 0x00FF;
    	}
    	else if (ui32Index == 1)
    	{
    		SSIDataGet(SSI0_BASE, &pui32DataRx[1]);
    		pui32DataRx[1] &= 0x00FF;
    	}
    	else
    	{
    		SSIDataGet(SSI0_BASE, &pui32DataRx[2]);
    		pui32DataRx[2] &= 0x00FF;

    	}

        //
        // Display the data that SSI0 received.
        //
        //UARTprintf("'%x'\n", (pui32DataRx[2] | (pui32DataRx[1] << 8)|(pui32DataRx[0]<<16)));
    }
    uint32_t a = (pui32DataRx[2] | (pui32DataRx[1] << 8) | (pui32DataRx[0] << 16));
    lettura = a * 0.0000001788;
    UARTprintf("'%c'\n", lettura);

    //
    // Return no errors
    //
    //return(0);
}
}