FAQ

Frequently Asked Questions

Common questions about LightOS RTOS.

General

What is LightOS?

LightOS is a modern C++20 real-time operating system designed for safety-critical embedded systems. It supports ARM Cortex-R52 and RISC-V architectures with hardware-verified reliability.

Is LightOS open source?

Yes! LightOS is available under the MIT license. See our GitHub repository.

What architectures are supported?

What’s the minimum memory footprint?

Development

What compiler do I need?

How do I run tests?

cmake -B build
cmake --build build
./build/lightos_unit_tests

All 1122 tests should pass.

Can I use LightOS with my existing C code?

Yes! LightOS provides both C++ and C APIs:

#include <lightos/lightos.h>

// C API
lightos_thread_create(task, NULL, 1024, 5);
lightos_scheduler_start();

Does LightOS support POSIX?

Yes, LightOS includes a POSIX compatibility layer:

Real-Time Performance

What’s the interrupt latency?

Does LightOS support preemption?

Yes, LightOS uses priority-based preemptive scheduling. Higher-priority threads preempt lower-priority ones immediately.

How many priority levels are there?

256 priority levels (0 = highest, 255 = lowest). The idle thread runs at priority 255.

Is there priority inheritance?

Yes, mutexes support priority inheritance to prevent priority inversion.

Safety & Certification

Is LightOS safety-certified?

LightOS is designed for safety-critical applications and follows MISRA C++ guidelines. Formal certification (ISO 26262, DO-178C) is available through our enterprise support.

What safety features are included?

Is there formal verification?

Yes, critical components are formally verified using model checking. See our UVM verification suite.

Build & Integration

How do I add LightOS to my project?

Option 1: Git submodule

git submodule add https://github.com/jiangintel-ux/lightOS.git

Option 2: CMake FetchContent

include(FetchContent)
FetchContent_Declare(lightos
    GIT_REPOSITORY https://github.com/jiangintel-ux/lightOS.git
    GIT_TAG main
)
FetchContent_MakeAvailable(lightos)
target_link_libraries(myapp lightos)

How do I configure features?

Use CMake options:

cmake -B build \
    -DLIGHTOS_POSIX_ENABLED=ON \
    -DLIGHTOS_SMP_ENABLED=ON \
    -DLIGHTOS_COVERAGE=ON

Can I disable features to reduce size?

Yes, most features can be disabled at compile time:

cmake -B build \
    -DLIGHTOS_POSIX_ENABLED=OFF \
    -DLIGHTOS_USB_ENABLED=OFF \
    -DLIGHTOS_CAN_ENABLED=OFF

Debugging

How do I debug on target?

LightOS supports:

How do I enable debug output?

#define LIGHTOS_DEBUG_ENABLED 1
#include <lightos/debug.hpp>

LIGHTOS_DEBUG("Value: %d", value);

Where are the trace scripts?

See scripts/trace32/ for Lauterbach TRACE32 scripts.

Troubleshooting

Build fails with “C++20 required”

Ensure you’re using a compatible compiler:

export CXX=g++-13
cmake -B build

Tests fail on host

Make sure you’re building in Debug mode:

cmake -B build -DCMAKE_BUILD_TYPE=Debug

QEMU doesn’t start

Install QEMU with ARM/RISC-V support:

# Ubuntu/Debian
sudo apt install qemu-system-arm qemu-system-misc

Getting Help