Introduction to Embedded Computing and Control

An embedded system is a dedicated computer system designed to perform one or a few specific functions — often with real-time computing constraints. Unlike a general-purpose desktop computer, an embedded system is embedded as part of a complete device, frequently including hardware and mechanical components.

Embedded systems are ubiquitous: they power microwave ovens, anti-lock braking systems, medical pacemakers, industrial conveyor belts, and robotic arms. In robotics, virtually every subsystem — motor drivers, sensor interfaces, safety interlocks, communication stacks — relies on an embedded processor.

Key characteristics of embedded systems:

• Real-time operation: responses must occur within defined time bounds (soft or hard deadlines)
• Resource constraints: limited RAM, flash, CPU cycles, and power
• Reliability: often must run continuously for years without human intervention
• Low-level hardware access: direct manipulation of GPIO pins, timers, interrupts, and peripherals

A control loop is the fundamental pattern of embedded control software:

while (true) {
    read_sensors();       // sample physical world
    compute_control();    // run control algorithm (e.g., PID)
    write_actuators();    // drive motors, valves, LEDs
    wait_until_next_tick(); // maintain fixed sample rate
}

The sample rate (loop frequency) must be fast enough relative to the system dynamics. A rule of thumb is to sample at least 10× the bandwidth of the controlled process. Industrial servo drives typically run at 1–20 kHz; mobile robot base controllers at 100–500 Hz.

Hard real-time systems guarantee a worst-case response time — missing a deadline causes system failure (e.g., engine ignition timing, surgical robot). Soft real-time systems tolerate occasional deadline misses with degraded — but acceptable — performance (e.g., video streaming buffer).