Writing firmware.
WHAT LANGUAGES DOMINATE
C, overwhelmingly C++, in larger systems Rust, increasingly, for memory safety Assembly, for specific routines
WHAT TO AVOID
Dynamic allocation after initialisation Recursion, where stack depth is unbounded Blocking operations in interrupt handlers Floating point, where the hardware lacks it
WHAT INTERRUPT HANDLERS MUST BE
Short, and non-blocking.
WHAT THEY SHOULD DO
Record what happened, and signal the main loop.
WHY
Long handlers delay other interrupts and cause missed events.
WHAT VOLATILE MEANS
A value that may change outside the program's control.
WHERE IT IS REQUIRED
Hardware registers, and variables shared with interrupt handlers.
WHAT HAPPENS WITHOUT IT
The compiler optimises away reads, and the program never sees changes.
WHAT A WATCHDOG TIMER DOES
Resets the system if not periodically reset by software.
WHY IT MATTERS
An unattended device that has hung must recover itself.
WHAT TO BE CAREFUL WITH
Resetting the watchdog in a place that continues running when the system is actually stuck.
WHAT TO TEST
Behaviour on power loss mid-operation.
