Embedded Systems & IoT

It tells the compiler a variable may change outside the program's control (hardware registers, ISRs), so it must not optimise away reads/writes.

An interrupt is a hardware/software signal that pauses normal execution; the Interrupt Service Routine handles it. ISRs should be short and defer heavy work.

UART is simple asynchronous point-to-point serial. I2C uses two wires and addresses for many devices at moderate speed. SPI uses more wires but is faster and full-duplex.

A real-time operating system schedules tasks with predictable timing. Use it when you have multiple concurrent tasks with deadlines; simple devices can use a super-loop.

When shared data is accessed concurrently and the result depends on timing. Prevent it with critical sections, disabling interrupts briefly, mutexes or atomic operations.

The stack holds local variables and call frames; the heap holds dynamic allocations. Many embedded systems avoid heap allocation to prevent fragmentation and unpredictable timing.

Use sleep modes, lower clock speeds, turn off unused peripherals, use interrupts instead of polling, and batch radio transmissions.

A hardware timer that resets the system if software stops 'kicking' it, recovering from hangs.

Check reset-cause registers, power supply stability, watchdog, stack overflow, hard-fault handlers and logs; reproduce under controlled conditions.

A lightweight publish–subscribe messaging protocol for IoT. Devices publish to topics on a broker, and subscribers receive messages, with QoS levels for reliability.