How do I debug unexpected resets in a STM32 device?
I'm doing some development in C with a STM32F107 chip and, at some point, the device began to reset when I call a specific function. I don't have a debugger and my debugging is just plain text over a serial port.
I've used some other microcontrollers in which I was able to access a register to see the cause of the reset, but I can't seem to find an equivalent for this device. I'm aware of the hardware exceptions of the Cortex-M3, but I don't know if one of them is being triggered since I can't seem to send text over usart when I'm inside those handlers (maybe because my TX functions use interruptions?).
So, I decided to ask people with more experience than I in this device: what is usually done to debug situations like these?
EDIT
One of the developers activated the WWDG watchdog and it was reseting the hardware before I could get my info from the fault handlers. It was a Hard Fault due to calling a function by a pointer that was pointing to the wrong place. However, I will keep this question in the hope that someone will give more details (or material about it) for pointing back to C code from the registers saved in, lets say, a Hard Fault (@dwelch idea).
Answer
The Cortex M3 has excellent fault handling features that will make your life easier. On hitting a fault, it automatically stacks several registers like PC and LR, and fault status registers will tell you things like address of bus fault, etc.
You should implement a good fault handler (for example, the hard fault handler here: http://blog.frankvh.com/2011/12/07/cortex-m3-m4-hard-fault-handler/) to print out the stacked registers and debug fault status registers.
You should use the UART for printing, just write your own simple custom version of printf for use from your fault handler that doesn't depend on interrupts. Just write bytes directly to uart Tx data register and poll for byte completion.