My STM32F429 seems to be stuck in a lockup state. When I start the debugger in TrueSTUDIO, it halts in startup_stm32f429.s at the second instruction in the Reset_Handler. I'm unable to step through the code at all. I tried stepping through the with the stlink utility, but I get a message at the bottom saying either "halted" or "lockup". All of the registers read as 0x(null). How do I get out of this lockup state?