2 docs tagged with "reset"

There is a gap between the moment power reaches the chip and the moment your first instruction executes, and firmware engineers habitually treat it as empty. It is not. In that gap the supply supervisor decides whether the rail is trustworthy, a pulse generator stretches whatever event caused the reset into a signal long enough for every block on the die to see it, an option-byte loader runs, boot-mode pins are sampled and latched, an address decoder is reconfigured so that a completely different memory appears at address zero, and only then does the CPU fetch two words and start running.

C has a set of guarantees that programmers stop noticing after the first month. Initialised globals hold their initialisers. Uninitialised globals are zero. The stack works. printf has somewhere to write. Static C++ objects have had their constructors run before main starts. On a hosted system a program loader and a crt0 object you have never opened deliver all of that before your first line executes.