Bare-metal programming means writing software that runs directly on the hardware with no operating system underneath it.1
Overview
On a microcontroller, bare-metal code is the firmware itself: it configures the chip’s peripheral registers by hand, manages its own memory, and typically runs as a “super loop” — an endless main loop that does work, with interrupts handling time-critical events. There is no scheduler, no driver model, and no abstraction between your code and the silicon, which means total control and minimal overhead, but also total responsibility for timing and correctness.
The two structural tools are polling — the loop repeatedly checking a flag or input — and interrupts, which let hardware pull the processor aside the instant something needs attention. Getting the balance right between them is much of the craft of bare-metal work.
Bare metal versus an RTOS
The same chip can run either way; the choice is about how many concurrent jobs the firmware must juggle:
| Aspect | Bare metal | With an RTOS |
|---|---|---|
| Structure | One super loop + interrupts | Multiple scheduled tasks |
| Overhead | Essentially none | A few KB of code and RAM |
| Concurrency | Hand-managed | Scheduler handles it |
| Boot time | Instant | Near-instant |
| Best for | Simple, tiny, timing-critical | Many competing deadlines |
Where it fits
Bare metal is the right choice for the simplest, smallest, or most timing-sensitive embedded systems, where an OS would only add size and unpredictability. It boots instantly and wastes no resources. The cost shows up as a project grows: juggling many concurrent jobs by hand becomes error-prone, which is the point at which developers adopt a real-time operating system. New firmware is loaded by in-system programming or a bootloader. The small radios and sensors whose signals GopherTrunk decodes are very often bare-metal devices — a single loop is all their one job requires.
Sources
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Bare machine — Wikipedia, on running software directly on hardware. ↩