What is a bootloader and what are its functions?

A bootloader is a small program stored in protected memory that runs first when a device powers on, responsible for initializing hardware and loading the main application. Functions: Initialize essential hardware (clock, memory, peripherals). Perform power-on self-test (POST). Load main application from Flash to RAM if needed. Provide firmware update capability (via UART, USB, CAN, OTA). Validate application integrity (CRC, signature). Select between multiple applications (A/B updates). Enter recovery mode if main application is corrupted. Common bootloaders include U-Boot (Linux), MCUboot, and vendor-specific ones. Bootloader typically resides in write-protected memory to prevent bricking the device.