How to know why nios has been reseted

Hello,

I have some trouble, my nios is reseted and my software restarts. I really don't know why it happens since my soft (under uC/OSII) uses only one task (plus niche stack) and it is blocking on a recv.

I will not explain in which case it reboots because I am more interesting (for this problem and others) to find a way to know why nios is reseted ? Is it possible to have a kind of core dump ? Can we do this with gdb ?