Real-time operating system (RTOS)

Simple firmware can run as a "superloop": read sensors, update outputs, repeat, with interrupts handling urgent events. As a product grows (wireless stack, user interface, logging, several control loops), juggling everything in one loop gets fragile. An RTOS splits work into tasks with priorities, so a time-critical control loop runs on schedule even while the radio is busy.

"Real-time" means predictable, not necessarily fast: the system is designed to respond within a known worst-case time. Several widely used RTOSes are open source; safety-certified options are usually commercial.

Where it bites: an RTOS adds memory use and new classes of bugs such as priority inversion, deadlocks and stack overflows. Wireless chip software stacks often require a particular RTOS, which can make the choice for you.