TM4C1294KCPDT: Reset following external clock failure

Hi BB_,

 I modified the existing TivaWware watchdog example to use the WD1 instead of WD0. The WD1 runs off of the PIOSC. I actually cannot reproduce your finding. I only have the launchpad with me. Once the example is running, I force the OSC0 to ground. I can see the reset -- the simulated POR reset actually happened.  If you have a chance please also try it. You can refer to the original watchdog example under <TivaWare_Installation>/examples/boards/ek-tm4c1294xl/watchdog. Below code is what I modified to use WD1.

#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/debug.h"
#include "driverlib/fpu.h"
#include "driverlib/gpio.h"
#include "driverlib/interrupt.h"
#include "driverlib/sysctl.h"
#include "driverlib/watchdog.h"
#include "driverlib/rom.h"
#include "driverlib/rom_map.h"
#include "drivers/buttons.h"

//*****************************************************************************
//
//! \addtogroup example_list
//! <h1>Watchdog (watchdog)</h1>
//!
//! This example application demonstrates the use of the watchdog as a simple
//! heartbeat for the system.  If the watchdog is not periodically fed, it will
//! reset the system.  Each time the watchdog is fed, the LED is inverted so
//! that it is easy to see that it is being fed, which occurs once every
//! second.  To stop the watchdog being fed and, hence, cause a system reset,
//! press the SW1 button.
//
//*****************************************************************************

//****************************************************************************
//
// System clock rate in Hz.
//
//****************************************************************************
uint32_t g_ui32SysClock;

//*****************************************************************************
//
// Flag to tell the watchdog interrupt handler whether or not to clear the
// interrupt (feed the watchdog).
//
//*****************************************************************************
volatile bool g_bFeedWatchdog = true;

//*****************************************************************************
//
// The error routine that is called if the driver library encounters an error.
//
//*****************************************************************************
#ifdef DEBUG
void
__error__(char *pcFilename, uint32_t ui32Line)
{
}
#endif

//*****************************************************************************
//
// The interrupt handler for the watchdog.  This feeds the dog (so that the
// processor does not get reset) and winks the LED connected to GPIO B3.
//
//*****************************************************************************
void
WatchdogIntHandler(void)
{
    //
    // If we have been told to stop feeding the watchdog, return immediately
    // without clearing the interrupt.  This will cause the system to reset
    // next time the watchdog interrupt fires.
    //
    if(!g_bFeedWatchdog)
    {
        return;
    }

    //
    // Clear the watchdog interrupt.
    //
    ROM_WatchdogIntClear(WATCHDOG1_BASE);

    //
    // Invert the GPIO PN0 value.
    //
    ROM_GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_0,
                     (ROM_GPIOPinRead(GPIO_PORTN_BASE, GPIO_PIN_0) ^
                                     GPIO_PIN_0));
}

//*****************************************************************************
//
// This function is called when the SW1 button is pressed.
//
//*****************************************************************************
static int32_t
SW1ButtonPressed(void)
{
    //
    // Set the flag that tells the interrupt handler not to clear the
    // watchdog interrupt.
    //
    g_bFeedWatchdog = false;

    return(0);
}

//*****************************************************************************
//
// This example demonstrates the use of the watchdog timer.
//
//*****************************************************************************
int
main(void)
{
    //
    // Set the clocking to run directly from the crystal at 120MHz.
    //
    g_ui32SysClock = MAP_SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                             SYSCTL_OSC_MAIN |
                                             SYSCTL_USE_PLL |
                                             SYSCTL_CFG_VCO_480), 16000000);
    //
    // Initialize the buttons driver.
    //
    ButtonsInit();

    //
    // Enable the peripherals used by this example.
    //
    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_WDOG1);
    ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPION);

    //
    // Enable processor interrupts.
    //
    ROM_IntMasterEnable();

    //
    // Set GPIO PN0 as an output.  This drives an LED on the board that will
    // toggle when a watchdog interrupt is processed.
    //
    ROM_GPIOPinTypeGPIOOutput(GPIO_PORTN_BASE, GPIO_PIN_0);
    ROM_GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_0, 0);

    //
    // Enable the watchdog interrupt.
    //
    ROM_IntEnable(INT_WATCHDOG);

    //
    // Set the period of the watchdog timer to 1 second.
    //
    ROM_WatchdogReloadSet(WATCHDOG1_BASE, g_ui32SysClock);

    //
    // Enable reset generation from the watchdog timer.
    //
    ROM_WatchdogResetEnable(WATCHDOG1_BASE);

    // Enable stall during debug mode
    WatchdogStallEnable(WATCHDOG1_BASE);

    //
    // Enable the watchdog timer.
    //
    ROM_WatchdogEnable(WATCHDOG1_BASE);

    //
    // Loop forever while the LED winks as watchdog interrupts are handled.
    //
    while(1)
    {
        //
        // Poll for the select button pressed
        //
        uint8_t ui8Buttons = ButtonsPoll(0, 0);
        if(ui8Buttons & USR_SW1)
        {
            SW1ButtonPressed();
            while(1)
            {
            }
        }
    }
}

I grounded the OSC0 by connecting the C44 terminal to ground. The example is supposed to toggle a LED. If reset happened, the LED will stop.