Beyond Main: Deconstructing the Cortex-M Startup Sequence from The Very First Cycle

For most embedded engineers, the application begins at main(). Everything before that is treated as "vendor magic": a black box of assembly and obscure C macros that we are afraid to touch.

In this session, we will open this black box and trace the exact lifecycle of Cortex-M microcontrollers from the very first clock cycle.

We will dissect the anatomy of a boot sequence, moving beyond the simple "copy .data / zero .bss" path to explore the darker corners of system initialization. How the VTOR works, the specific roles of MSP vs. PSP stack pointers, TrustZone setup before the first jump, and the "IDE Lock-in" - how vendor-specific startup files create hidden dependencies that make migrating from one IDE or toolchain to another a nightmare of broken builds.

Whether you are writing a bare-metal bootloader, debugging a complex crashing RTOS application or porting your project from one IDE to another, understanding life before main is the key to reliable and secure firmware.