Dear Sirs
My problem was exactly the same as in the related post "TM4C1292NCPDT: I am not able to debug TM4c1292NCPDT through JTAG". The unlock procedure work as advertised. Thank you. As with Mr. shaikh, I didn't have the JTAG pins assigned to any other purpose, the controller was never put into any sort of sleep mode, and I haven't configured BOOTCFG in my application. However, I knew it had to be related to my code. I found the offending line of code, see below.
int
main(void)
{
// uint32_t i;
uint32_t time_ms;
uint32_t ticks;
// uint32_t hexFloatData1, hexFloatData2;
// float floatData1, floatData2;
//
// Run from the PLL at 120 MHz.
// Note: SYSCTL_CFG_VCO_240 is a new setting provided in TivaWare 2.2.x and
// later to better reflect the actual VCO speed due to SYSCTL#22.
//
/* g_ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
SYSCTL_OSC_MAIN |
SYSCTL_USE_PLL |
SYSCTL_CFG_VCO_240), 120000000);*/
g_ui32SysClock = SysCtlClockFreqSet((SYSCTL_OSC_INT | SYSCTL_USE_PLL |SYSCTL_CFG_VCO_480), 120000000);
//
// Set up the serial console to use for displaying messages.
//
ConfigureUART();
The commented-out line of code that configures the system clock is the code that causes the problem. The code line that follows, that configures the system clock, works fine and doesn't lock up the controller. There is a 25MHz oscillator on the board, see attached schematic. Why would this cause a problem? Thank you for your time.
