system_flush() aborting in ISR and SWI

/****************************************************************************/
/* ABORT - ABNORMAL PROGRAM TERMINATION.  CURRENTLY JUST HALTS EXECUTION.   */
/****************************************************************************/
void abort(void)
{
   /*-------------------------------------------------------------------*/
   /* SET C$$EXIT LABEL SO THE DEBUGGER KNOWS WHEN THE C++ PROGRAM HAS  */
   /* COMPLETED.  THIS CAN BE REMOVED IF THE DEBUGGER IS NOT USED.      */
   /*-------------------------------------------------------------------*/
   __asm("        .global C$$EXIT");
   __asm("C$$EXIT: nop");

   for (;;);   /* SPINS FOREVER */
}

/*
 *  ======== main.c ========
 */

#include <xdc/std.h>
#include <ti/sysbios/BIOS.h>
#include <xdc/cfg/global.h>
#include <xdc/runtime/System.h>
#include <xdc/runtime/Log.h>

#include <driverlib.h>

#define GPIO_ALL	GPIO_PIN0|GPIO_PIN1|GPIO_PIN2|GPIO_PIN3| \
					GPIO_PIN4|GPIO_PIN5|GPIO_PIN6|GPIO_PIN7

uint8_t returnValue = 0x00;
uint8_t transmitData = 0x00,
		receiveData = 0x00;

void init_GPIO(void);
int init_SPI(void);
void start_SPI(void);
void SPI_ISR(void);

//-----------------------------------------
// Globals
//-----------------------------------------
volatile int16_t i16ToggleCount = 0;

/*
 *  ======== main ========
 */
Int main()
{ 
	init_GPIO();
	init_SPI();
	
	System_printf("You are in!");
	System_flush();

    BIOS_start();    /* does not return */
    return(0);
}

void start_SPI(){
	char rx_char= {'0'};

	rx_char= USCI_A_SPI_receiveData(USCI_A0_BASE);

	if( rx_char == 0x50){
   		GPIO_toggleOutputOnPin(GPIO_PORT_P4,GPIO_PIN7);
   	} else{
   		GPIO_toggleOutputOnPin(GPIO_PORT_P1,GPIO_PIN0);
  	}

	System_putch(rx_char);

	if( rx_char == '!' ){
		System_putch(rx_char);

		USCI_A_SPI_disableInterrupt(USCI_A0_BASE, USCI_A_SPI_RECEIVE_INTERRUPT);
		// System_flush();
		// USCI_A_SPI_enableInterrupt(USCI_A0_BASE, USCI_A_SPI_RECEIVE_INTERRUPT);
	}

//	System_flush();
}

int init_SPI(){
	// Configure for SPI
	// P3.4 as MISO
	GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P3,GPIO_PIN4);
	// P3.3 as MOSI
	GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_P3,GPIO_PIN3);
	// P2.7 as SCLK
	GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_P2,GPIO_PIN7);
    // P6.6 Chip select
    GPIO_setAsInputPin(GPIO_PORT_P6,GPIO_PIN6);

    returnValue = USCI_A_SPI_initSlave( USCI_A0_BASE, USCI_A_SPI_MSB_FIRST, USCI_A_SPI_PHASE_DATA_CHANGED_ONFIRST_CAPTURED_ON_NEXT,
    		USCI_A_SPI_CLOCKPOLARITY_INACTIVITY_LOW );

    if(STATUS_FAIL == returnValue){
    	return 0;
    }

    // Enable SPI Module
    USCI_A_SPI_enable(USCI_A0_BASE);

    // Enable Receive Interrupt
    USCI_A_SPI_clearInterrupt(USCI_A0_BASE, USCI_A_SPI_RECEIVE_INTERRUPT); // Flag may be needed or not
    USCI_A_SPI_enableInterrupt(USCI_A0_BASE, USCI_A_SPI_RECEIVE_INTERRUPT);

    return 1;
}

void init_GPIO(void){
	// Disable the Watchdog Timer (important, as this is enabled by default)
	WDT_A_hold( WDT_A_BASE );

	// Set GPIO ports to low-level outputs
    GPIO_setAsOutputPin( GPIO_PORT_P1, GPIO_PIN0 );
    GPIO_setAsOutputPin( GPIO_PORT_P4, GPIO_PIN7 );
    GPIO_setOutputLowOnPin( GPIO_PORT_P1, GPIO_PIN0 );
    GPIO_setOutputLowOnPin( GPIO_PORT_P4, GPIO_PIN7 );
}

void SPI_ISR(void)
{
	Swi_post(SPISwi);
	USCI_A_SPI_clearInterrupt(USCI_A0_BASE, USCI_A_SPI_RECEIVE_INTERRUPT); // Flag may be needed or not
}