ROM_updateUSB on TM4C1294NCPDT running TiRTOS

Hi,

I have custom software running with TiRTOS on a TM4C1264NCPDT and I want to run the ROM_updateUSB(0) from my code in order to get into DFU mode and do a firmware update.

There are several posts about this and this is the code I am using derived from these posts...

//-----------------------------------------------------------------------------------
void enterBootloader(void)
{
int ui32Addr;

    ROM_IntMasterDisable();
    ROM_SysTickIntDisable();
    ROM_SysTickDisable();
    ROM_SysCtlPeripheralDisable(SYSCTL_PERIPH_USB0);

    HWREG(NVIC_DIS0) = 0xffffffff;
    HWREG(NVIC_DIS1) = 0xffffffff;
    HWREG(NVIC_DIS2) = 0xffffffff;
    HWREG(NVIC_DIS3) = 0xffffffff;
    HWREG(NVIC_DIS4) = 0xffffffff;
    for(ui32Addr = NVIC_PRI0; ui32Addr <= NVIC_PRI34; ui32Addr+=4) {
       HWREG(ui32Addr) = 0;
    }
    HWREG(NVIC_SYS_PRI1) = 0;
    HWREG(NVIC_SYS_PRI2) = 0;
    HWREG(NVIC_SYS_PRI3) = 0;

    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOL);	//
    while(!ROM_SysCtlPeripheralReady(SYSCTL_PERIPH_GPIOL))
    {
    }
    ROM_GPIOPinTypeUSBAnalog(GPIO_PORTL_BASE, GPIO_PIN_6 | GPIO_PIN_7);

    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_USB0);
    while(!ROM_SysCtlPeripheralReady(SYSCTL_PERIPH_USB0))
    {
    }
    ROM_SysCtlPeripheralReset(SYSCTL_PERIPH_USB0);
    SysCtlUSBPLLEnable();
    ROM_SysCtlDelay(40000000);

    ROM_IntMasterEnable();
    ROM_UpdateUSB(0);
    while(1)
        {
        }
}

I am calling this from the USBCDCD thread (the command to go into bootloader is a serial port message from the host).

My problem is that this does not appear to run the bootloader in DFU mode until I power-cycle it.

Can anybody tell me what I am doing wrong please.

Thanks
Richard