Timers

A timer is a device or software mechanism that measures time intervals and triggers actions when specified times elapse. Hardware timers are built into processors or microcontrollers and rely on a fixed clock source. They can generate periodic interrupts, measure elapsed time, or control peripherals such as PWM. Software timers are implemented by the operating system or runtime and rely on the system clock; they schedule callbacks or wake tasks after delays.

Timers come in several basic forms. One-shot timers trigger once after a delay, while periodic timers fire at regular intervals. Monotonic timers increase steadily and are immune to changes in the system clock, whereas wall-clock or calendar timers reflect real-world time and can jump if the clock is adjusted. Timers are often organized with data structures such as priority queues or timer wheels to manage many events efficiently.

In computing environments, timers drive scheduling, timeouts, and delays. A timer interrupt is generated by a hardware timer to implement preemption and scheduling in operating systems. In embedded systems, timers control input capture, PWM generation, and event timing. In software, timer services provide functions such as sleep, delay, setTimeout, or promise-based timers. High-resolution timers offer greater accuracy but may incur higher overhead; jitter and latency describe variability in timer responses.

Common challenges include timer overflow and wraparound, drift between clocks, and synchronization when clocks change. Solutions include using monotonic clocks for elapsed-time measurements, calibrating timers, and employing multiple timers or watchdog mechanisms for critical schedules.