Compare RTOS Platforms

RTOS Comparison

See how LightOS compares to other popular RTOS platforms for silicon validation and embedded firmware.

Quick Comparison

FeatureLightOSFreeRTOSZephyrThreadX
Boot Time<5μs~100μs~1ms~50μs
Min RAM~2KB~5KB~8KB~2KB
Min Flash~4KB~6KB~50KB~10KB
ISR jitter, FIQ (Cortex-R52, 100 Hz tick, n=16,384)3 cyc / 5 ns p2p, IQR 1 cyc1n/a publishedn/a published10 cyc / 17 ns p2p, IQR 1 cyc
ISR jitter, IRQ (Cortex-R52, 100 Hz tick, steady-state n=16,126)1 cyc / 1.7 ns p2p, IQR 1 cyc1n/an/a~17 cyc / 28 ns p2p
Coop ctx-switch, scheduler-mediated (apples-to-apples)182.5 cyc / 304 ns / switchn/an/a199.5 cyc / 333 ns / switch
Coop ctx-switch, explicit-target (yield_to(target))85.5 cyc / 143 ns / switch — 2.33× fastern/an/an/a (no equivalent)
Coop ctx-switch fan-out scaling (m06, equal-priority N=2..64 round-robin, Cortex-R52, n=1008/N post-warmup)flat 192–198 cyc / switch from N=2 to N=64; LightOS leads at every N2n/a publishedn/a publishedflat 193–206 cyc / switch (also O(1))
Coop ctx-switch under 100 kHz IRQ load (m04, yield_to(target) while servicing 13 M IRQs)90 cyc / 150 ns / switch (+5.3 %) — tail bounded at 397 cyc/switchn/a publishedn/a publishedn/a published
Coop ctx-switch under 1 kHz IRQ load (m04b cadence sweep, yield_to(target) while servicing 39,612 IRQs)90 cyc / 150 ns / switch — jitter 15 cyc / 25 ns, collapses to m02 floor (zero in-window collisions)n/a publishedn/a publishedn/a published
App-thread wake jitter (sleep_until)31 cyc / 52 ns p2p, IQR 4 cyc — ~3.8× tightern/an/a~117 ns p2p (tx_thread_sleep)
LanguageC++20C99C99C99
Unit Tests5720~500~5000~200
LicenseProprietaryMITApache 2.0MIT
Safety CertASIL-D readyMISRASIL-3ASIL-D
Rust Bindings✅ NativeCommunityExperimental❌

Boot Time Comparison

LightOS: 5 FreeRTOS: 100 Zephyr: 1000 ThreadX: 50

Why boot time matters for silicon validation:

Memory Footprint

Minimum Configuration

RTOSRAMFlashNotes
LightOS2KB4KBMinimal kernel (scheduler + 1 thread)
FreeRTOS5KB6KBMinimal config
Zephyr8KB50KBMinimal config (larger due to subsystems)
ThreadX2KB10KBAbsolute minimum

Typical Validation Configuration

RTOSRAMFlashNotes
LightOS32KB20KB4 threads, queues, timers, IRQ
FreeRTOS20KB15KBSimilar config
Zephyr40KB80KBSubsystem overhead
ThreadX15KB25KBSimilar config

Feature Comparison

Scheduler

FeatureLightOSFreeRTOSZephyrThreadX
Priority Levels3232+32+32
Preemption✅✅✅✅
Time Slicing✅✅✅✅
Priority Inheritance✅✅✅✅
Tickless Idle✅✅✅✅
O(1) Scheduling✅❌✅✅

Synchronization

FeatureLightOSFreeRTOSZephyrThreadX
Mutex✅✅✅✅
Semaphore✅✅✅✅
Message Queue✅✅✅✅
Event Groups✅✅✅✅
Condition Variables✅❌✅❌

Architecture Support

ArchitectureLightOSFreeRTOSZephyrThreadX
ARM Cortex-R✅✅✅✅
ARM Cortex-A✅✅✅✅
ARM Cortex-M✅✅✅✅
RISC-V 64-bit✅✅✅✅
RISC-V 32-bit✅✅✅✅
x86Host tests✅✅❌

Developer Experience

API Style

LightOS (C++20):

#include <lightos/thread.hpp>

lightos::thread worker("Worker", priority::normal, [](void*) {
    while (true) {
        auto msg = queue.receive(timeout::infinite);
        process(msg);
    }
});
worker.start();

FreeRTOS (C99):

#include "FreeRTOS.h"
#include "task.h"

void worker_task(void* param) {
    while (1) {
        Message msg;
        xQueueReceive(queue, &msg, portMAX_DELAY);
        process(&msg);
    }
}
xTaskCreate(worker_task, "Worker", 256, NULL, 1, &handle);

Zephyr (C99):

#include <zephyr/kernel.h>

void worker_thread(void* p1, void* p2, void* p3) {
    while (1) {
        struct message msg;
        k_msgq_get(&queue, &msg, K_FOREVER);
        process(&msg);
    }
}
K_THREAD_DEFINE(worker_id, 1024, worker_thread, NULL, NULL, NULL, 5, 0, 0);

Testing & Quality

MetricLightOSFreeRTOSZephyrThreadX
Unit Tests5720~500~5000~200
CI/CDGitHub ActionsGitHub ActionsGitHub ActionsAzure Pipelines
Code Coverage85%+~80%~90%~70%
Static Analysiscppcheck, clang-tidyPC-lintCoverityInternal
Formal VerificationSVA (scheduler, mutex)LimitedLimited❌

Use Case Fit

Silicon Validation

CriterionLightOSFreeRTOSZephyrThreadX
Boot Speed⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐
Simulation-Aware⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐
Determinism⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐
OverallBestGoodFairVery Good

Embedded Firmware

CriterionLightOSFreeRTOSZephyrThreadX
Ecosystem⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐
Community⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐
Modern API⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐
OverallGoodVery GoodBestGood

Migration Guides

From FreeRTOS

From Zephyr

From ThreadX

Ready to Evaluate?

Request Evaluation Schedule Demo

Disclaimer: Performance metrics and comparisons are based on internal testing under specific test conditions and may vary depending on hardware, configuration, and workload. Third-party product information is based on publicly available data and may not reflect the latest versions.

Trademarks: FreeRTOS is a registered trademark of Amazon Web Services. Zephyr is a trademark of the Linux Foundation. ThreadX is a trademark of Microsoft Corporation. ARM and Cortex are trademarks of Arm Limited. RISC-V is a registered trademark of RISC-V International. All other trademarks are the property of their respective owners. LightOS is not affiliated with or endorsed by any of these trademark holders.

  1. Benchmark-grade build with LIGHTOS_FIQ_HOOK_DISABLED / LIGHTOS_IRQ_HOOK_DISABLED elides the default weak-symbol bring-up hooks from the ISR entry path. Shipping default build measures 21 cyc (FIQ) / 32 cyc (IRQ) raw peak-to-peak with the same 1-cycle IQR. IRQ steady state excludes the first 256 warmup samples (I-cache cold-fill) and TRACE32-halt-correlated paired outliers. ↩︎ ↩︎

  2. Cooperative context-switch fan-out (m06) measured on Arm Cortex-R52 silicon at 600 MHz with the m02 PMCCNTR-delta harness extended to N equal-priority threads chained through a single ready-queue. Per-switch p50 (cyc, n=1008 post-warmup): LightOS Scheduler::yield() 182.5 / 197.8 / 194.9 / 193.3 / 192.6 / 192.4 across N=2/4/8/16/32/64; ThreadX 6.4 tx_thread_relinquish() 199.5 / 206.2 / 196.0 / 200.8 / 193.8 / 193.4 across the same range. IQR ≤ 0.2 cyc on LightOS, 0 cyc on ThreadX at every N. Both kernels are O(1); both asymptote at ≈ 193 cyc/switch as N grows. LightOS leads at every measured N, by 1.005× to 1.09×. ↩︎