EDF Scheduling with Constant-Bandwidth Servers in Apache NuttX: Design, Implementation, and Virtual-Time Evaluation

Abstract

We present a uniprocessor earliest-deadline-first (EDF) scheduling policy with per-task constant-bandwidth servers (CBS) for Apache NuttX. The integration combines absolute-deadline ordering, execution-time accounting, budget throttling, watchdog-based replenishment, repayment of execution overrun debt, and admission control capped at 95 percent of one processor for implicit-deadline reservations (D = P).

An injected-time transition check and deterministic QEMU instruction-count virtual time exercise the implementation at the scheduler and kernel levels. In a 1.8-second budget-enforcement experiment, two protected periodic tasks completed all 75 jobs on time while an over-demanding server generated 20 throttles and 19 replenishments within the observation window. In a separate higher-utilization, 190-job comparison on the same traced firmware, NuttX sporadic scheduling missed four deadlines; EDF/CBS met all 190.

The released source, transition evidence, firmware identity, and traces establish a reproducible experimental baseline for deadline-oriented, budget-enforced scheduling in Apache NuttX.