diff --git a/src/platforms/posix/lockstep_scheduler/.gitignore b/src/platforms/posix/lockstep_scheduler/.gitignore
new file mode 100644
index 0000000000..567609b123
--- /dev/null
+++ b/src/platforms/posix/lockstep_scheduler/.gitignore
@@ -0,0 +1 @@
+build/
diff --git a/src/platforms/posix/lockstep_scheduler/CMakeLists.txt b/src/platforms/posix/lockstep_scheduler/CMakeLists.txt
new file mode 100644
index 0000000000..33e8f70666
--- /dev/null
+++ b/src/platforms/posix/lockstep_scheduler/CMakeLists.txt
@@ -0,0 +1,38 @@
+cmake_minimum_required(VERSION 2.8.12)
+
+if(NOT PROJECT_NAME STREQUAL "px4")
+
+    project(lockstep_scheduler)
+
+    set (CMAKE_CXX_STANDARD 11)
+
+    add_library(lockstep_scheduler
+        src/lockstep_scheduler.cpp
+    )
+
+    target_include_directories(lockstep_scheduler
+        PUBLIC
+            $<INSTALL_INTERFACE:include>
+            $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+        PRIVATE
+            ${CMAKE_CURRENT_SOURCE_DIR}/src
+    )
+
+    target_link_libraries(lockstep_scheduler
+        pthread
+    )
+
+    target_compile_options(lockstep_scheduler PRIVATE -Wall -Wextra -Werror -O2)
+
+    add_subdirectory(test)
+
+else()
+
+    add_library(lockstep_scheduler
+        src/lockstep_scheduler.cpp
+    )
+    include_directories(
+        include
+    )
+
+endif()
diff --git a/src/platforms/posix/lockstep_scheduler/build-and-test.sh b/src/platforms/posix/lockstep_scheduler/build-and-test.sh
new file mode 100755
index 0000000000..dd92e0a764
--- /dev/null
+++ b/src/platforms/posix/lockstep_scheduler/build-and-test.sh
@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+
+set -e
+
+rm -rf build
+
+(mkdir -p build && cd build && CXX=g++ cmake .. && make -j8 && time $@ ./test/lockstep_scheduler_test)
+rm -rf build
+
+(mkdir -p build && cd build && CXX=clang++ cmake .. && make -j8 && time $@ ./test/lockstep_scheduler_test)
+rm -rf build
diff --git a/src/platforms/posix/lockstep_scheduler/include/lockstep_scheduler/lockstep_scheduler.h b/src/platforms/posix/lockstep_scheduler/include/lockstep_scheduler/lockstep_scheduler.h
new file mode 100644
index 0000000000..cbfa770070
--- /dev/null
+++ b/src/platforms/posix/lockstep_scheduler/include/lockstep_scheduler/lockstep_scheduler.h
@@ -0,0 +1,30 @@
+#pragma once
+
+#include <cstdint>
+#include <mutex>
+#include <vector>
+#include <memory>
+#include <atomic>
+#include <pthread.h>
+
+class LockstepScheduler {
+public:
+    void set_absolute_time(uint64_t time_us);
+    uint64_t get_absolute_time() const;
+    int cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *lock, uint64_t time_us);
+    int usleep_until(uint64_t timed_us);
+
+private:
+    std::atomic<uint64_t> time_us_{0};
+
+    struct TimedWait {
+        pthread_cond_t *passed_cond{nullptr};
+        pthread_mutex_t *passed_lock{nullptr};
+        uint64_t time_us{0};
+        bool timeout{false};
+        bool done{false};
+    };
+    std::vector<std::shared_ptr<TimedWait>> timed_waits_{};
+    std::mutex timed_waits_mutex_{};
+    bool timed_waits_iterator_invalidated_{false};
+};
diff --git a/src/platforms/posix/lockstep_scheduler/src/lockstep_scheduler.cpp b/src/platforms/posix/lockstep_scheduler/src/lockstep_scheduler.cpp
new file mode 100644
index 0000000000..7b1f065dc7
--- /dev/null
+++ b/src/platforms/posix/lockstep_scheduler/src/lockstep_scheduler.cpp
@@ -0,0 +1,116 @@
+#include "lockstep_scheduler/lockstep_scheduler.h"
+
+
+uint64_t LockstepScheduler::get_absolute_time() const
+{
+    return time_us_;
+}
+
+void LockstepScheduler::set_absolute_time(uint64_t time_us)
+{
+    time_us_ = time_us;
+
+    {
+        std::unique_lock<std::mutex> lock_timed_waits(timed_waits_mutex_);
+
+        auto it = std::begin(timed_waits_);
+        while (it != std::end(timed_waits_)) {
+
+            std::shared_ptr<TimedWait> temp_timed_wait = *it;
+
+            // Clean up the ones that are already done from last iteration.
+            if (temp_timed_wait->done) {
+                it = timed_waits_.erase(it);
+                continue;
+            }
+
+            if (temp_timed_wait->time_us <= time_us &&
+                    !temp_timed_wait->timeout &&
+                    !temp_timed_wait->done) {
+                temp_timed_wait->timeout = true;
+                // We are abusing the condition here to signal that the time
+                // has passed.
+                timed_waits_iterator_invalidated_ = false;
+                pthread_mutex_lock(temp_timed_wait->passed_lock);
+                pthread_cond_broadcast(temp_timed_wait->passed_cond);
+                pthread_mutex_unlock(temp_timed_wait->passed_lock);
+                if (timed_waits_iterator_invalidated_) {
+                    // The vector might have changed, we need to start from the
+                    // beginning.
+                    it = std::begin(timed_waits_);
+                    continue;
+                }
+            }
+            ++it;
+        }
+    }
+}
+
+int LockstepScheduler::cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *lock, uint64_t time_us)
+{
+    std::shared_ptr<TimedWait> new_timed_wait;
+    {
+        std::lock_guard<std::mutex> lock_timed_waits(timed_waits_mutex_);
+
+        // The time has already passed.
+        if (time_us <= time_us_) {
+            errno = ETIMEDOUT;
+            return -1;
+        }
+
+        new_timed_wait = std::make_shared<TimedWait>();
+        new_timed_wait->time_us = time_us;
+        new_timed_wait->passed_cond = cond;
+        new_timed_wait->passed_lock = lock;
+        timed_waits_.push_back(new_timed_wait);
+        timed_waits_iterator_invalidated_ = true;
+    }
+
+    while (true) {
+        int result = pthread_cond_wait(cond, lock);
+
+        // We need to unlock before aqcuiring the timed_waits_mutex, otherwise
+        // we are at rist of priority inversion.
+        pthread_mutex_unlock(lock);
+
+        {
+            std::lock_guard<std::mutex> lock_timed_waits(timed_waits_mutex_);
+
+            if (result == 0 && new_timed_wait->timeout) {
+                errno = ETIMEDOUT;
+                result = -1;
+            }
+
+            new_timed_wait->done = true;
+        }
+
+        // The lock needs to be locked on exit of this function
+        pthread_mutex_lock(lock);
+        return result;
+    }
+}
+
+int LockstepScheduler::usleep_until(uint64_t time_us)
+{
+    pthread_mutex_t lock;
+    pthread_mutex_init(&lock, NULL);
+    pthread_cond_t cond;
+    pthread_cond_init(&cond, NULL);
+
+    pthread_mutex_lock(&lock);
+
+    int result = cond_timedwait(&cond, &lock, time_us);
+
+    if (result == -1 && errno == ETIMEDOUT) {
+        // This is expected because we never notified to the condition.
+        errno = 0;
+        result = 0;
+    }
+
+    pthread_mutex_unlock(&lock);
+
+    pthread_cond_destroy(&cond);
+    pthread_mutex_destroy(&lock);
+
+    return result;
+}
diff --git a/src/platforms/posix/lockstep_scheduler/test/CMakeLists.txt b/src/platforms/posix/lockstep_scheduler/test/CMakeLists.txt
new file mode 100644
index 0000000000..ea779efc9e
--- /dev/null
+++ b/src/platforms/posix/lockstep_scheduler/test/CMakeLists.txt
@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 2.8.12)
+
+add_executable(lockstep_scheduler_test
+    src/lockstep_scheduler_test.cpp
+)
+
+target_link_libraries(lockstep_scheduler_test
+    lockstep_scheduler
+)
+
+target_compile_options(lockstep_scheduler_test PRIVATE -Wall -Wextra -Werror -O2)
diff --git a/src/platforms/posix/lockstep_scheduler/test/src/lockstep_scheduler_test.cpp b/src/platforms/posix/lockstep_scheduler/test/src/lockstep_scheduler_test.cpp
new file mode 100644
index 0000000000..f9b4973a27
--- /dev/null
+++ b/src/platforms/posix/lockstep_scheduler/test/src/lockstep_scheduler_test.cpp
@@ -0,0 +1,286 @@
+#include <lockstep_scheduler/lockstep_scheduler.h>
+#include <cassert>
+#include <thread>
+#include <atomic>
+#include <random>
+#include <iostream>
+
+
+constexpr uint64_t some_time_us = 12345678;
+
+void test_absolute_time()
+{
+    LockstepScheduler ls;
+    ls.set_absolute_time(some_time_us);
+    assert(ls.get_absolute_time() == some_time_us);
+}
+
+void test_condition_timing_out()
+{
+    // Create locked condition.
+    pthread_cond_t cond;
+    pthread_cond_init(&cond, NULL);
+
+    // And a lock which needs to be locked
+    pthread_mutex_t lock;
+    pthread_mutex_init(&lock, NULL);
+
+    LockstepScheduler ls;
+    ls.set_absolute_time(some_time_us);
+
+    std::atomic<bool> should_have_timed_out{false};
+    pthread_mutex_lock(&lock);
+
+    // Use a thread to wait for condition while we already have the lock.
+    // This ensures the synchronization happens in the right order.
+    std::thread thread([&ls, &cond, &lock, &should_have_timed_out]() {
+        assert(ls.cond_timedwait(&cond, &lock, some_time_us + 1000) == -1);
+        assert(errno == ETIMEDOUT);
+        assert(should_have_timed_out);
+        // It should be re-locked afterwards, so we should be able to unlock it.
+        assert(pthread_mutex_unlock(&lock) == 0);
+    });
+
+    ls.set_absolute_time(some_time_us + 500);
+    should_have_timed_out = true;
+    ls.set_absolute_time(some_time_us + 1500);
+
+    thread.join();
+
+    pthread_mutex_destroy(&lock);
+    pthread_cond_destroy(&cond);
+
+}
+
+void test_locked_semaphore_getting_unlocked()
+{
+    // Create locked condition.
+    pthread_cond_t cond;
+    pthread_cond_init(&cond, NULL);
+
+    // And a lock which needs to be locked
+    pthread_mutex_t lock;
+    pthread_mutex_init(&lock, NULL);
+
+    LockstepScheduler ls;
+    ls.set_absolute_time(some_time_us);
+
+    pthread_mutex_lock(&lock);
+    // Use a thread to wait for condition while we already have the lock.
+    // This ensures the synchronization happens in the right order.
+    std::thread thread([&ls, &cond, &lock]() {
+
+        ls.set_absolute_time(some_time_us + 500);
+        assert(ls.cond_timedwait(&cond, &lock, some_time_us + 1000) == 0);
+        // It should be re-locked afterwards, so we should be able to unlock it.
+        assert(pthread_mutex_unlock(&lock) == 0);
+    });
+
+    pthread_mutex_lock(&lock);
+    pthread_cond_broadcast(&cond);
+    pthread_mutex_unlock(&lock);
+
+    thread.join();
+
+    pthread_mutex_destroy(&lock);
+    pthread_cond_destroy(&cond);
+}
+
+class TestCase {
+public:
+    TestCase(unsigned timeout, unsigned unlocked_after, LockstepScheduler &ls) :
+        timeout_(timeout + some_time_us),
+        unlocked_after_(unlocked_after + some_time_us),
+        ls_(ls)
+    {
+        pthread_mutex_init(&lock_, NULL);
+        pthread_cond_init(&cond_, NULL);
+    }
+
+    ~TestCase()
+    {
+        assert(is_done_);
+        pthread_mutex_destroy(&lock_);
+        pthread_cond_destroy(&cond_);
+    }
+
+    void run()
+    {
+        pthread_mutex_lock(&lock_);
+        thread_ = std::make_shared<std::thread>([this]() {
+            result_ = ls_.cond_timedwait(&cond_, &lock_, timeout_);
+            pthread_mutex_unlock(&lock_);
+        });
+    }
+
+    void check()
+    {
+        if (is_done_) {
+            return;
+        }
+
+        uint64_t time_us = ls_.get_absolute_time();
+
+        const bool unlock_reached = (time_us >= unlocked_after_);
+        const bool unlock_is_before_timeout = (unlocked_after_ <= timeout_);
+        const bool timeout_reached = (time_us >= timeout_);
+
+        if (unlock_reached && unlock_is_before_timeout && !(timeout_reached)) {
+            pthread_mutex_lock(&lock_);
+            pthread_cond_broadcast(&cond_);
+            pthread_mutex_unlock(&lock_);
+            is_done_ = true;
+            // We can be sure that this triggers.
+            thread_->join();
+            assert(result_ == 0);
+        }
+
+        else if (timeout_reached) {
+            is_done_ = true;
+            thread_->join();
+            assert(result_ == -1);
+        }
+    }
+private:
+    static constexpr int INITIAL_RESULT = 42;
+
+    unsigned timeout_;
+    unsigned unlocked_after_;
+    pthread_cond_t cond_;
+    pthread_mutex_t lock_;
+    LockstepScheduler &ls_;
+    std::atomic<bool> is_done_{false};
+    std::atomic<int> result_ {INITIAL_RESULT};
+    std::shared_ptr<std::thread> thread_{};
+};
+
+int random_number(int min, int max)
+{
+    // We want predictable test results, so we always
+    // start with the seed 0.
+    static int iteration = 0;
+
+    std::seed_seq seed{iteration++};
+    std::default_random_engine engine{seed};
+    std::uniform_int_distribution<> distribution(min, max);
+
+    const int random_number = distribution(engine);
+    return random_number;
+}
+
+void test_multiple_semaphores_waiting()
+{
+
+    LockstepScheduler ls;
+    ls.set_absolute_time(some_time_us);
+
+    // Use different timeouts in random order.
+    std::vector<std::shared_ptr<TestCase>> test_cases{};
+
+    test_cases.push_back(
+        std::make_shared<TestCase>(
+            11111, 11111, ls));
+
+    test_cases.push_back(
+        std::make_shared<TestCase>(
+            20000, 20000, ls));
+
+    test_cases.push_back(
+        std::make_shared<TestCase>(
+            0, 20000, ls));
+
+    test_cases.push_back(
+        std::make_shared<TestCase>(
+            20000, 10000, ls));
+
+    test_cases.push_back(
+        std::make_shared<TestCase>(
+            0, 0, ls));
+
+    const int num_additional_threads = random_number(1, 20);
+
+    for (int i = 0; i < num_additional_threads; ++i) {
+        const unsigned timeout = random_number(1, 20000);
+        const unsigned unlocked_after = random_number(1, 20000);
+        test_cases.push_back(
+            std::make_shared<TestCase>(
+                timeout, unlocked_after, ls));
+    }
+
+    for (auto &test_case : test_cases) {
+        test_case->run();
+    }
+
+    const int min_step_size = 1;
+    const int max_step_size = 100;
+
+    // We need to go until the max plus max step size to make sure we trigger
+    // all timeouts or semaphores.
+    for (unsigned time_us = 1;
+         time_us <= (20000 + max_step_size);
+         time_us += random_number(min_step_size, max_step_size)) {
+
+        ls.set_absolute_time(some_time_us + time_us);
+
+        for (auto &test_case : test_cases) {
+            test_case->check();
+        }
+    }
+
+    test_cases.clear();
+}
+
+#define WAIT_FOR(condition_) \
+    while (!(condition_)) { \
+        std::this_thread::yield(); \
+    }
+
+void test_usleep()
+{
+    LockstepScheduler ls;
+    ls.set_absolute_time(some_time_us);
+
+    enum class Step {
+        Init,
+        ThreadStarted,
+        BeforeUsleep,
+        UsleepNotTriggeredYet,
+        UsleepTriggered
+    };
+
+    std::atomic<Step> step{Step::Init};
+
+    std::thread thread([&step, &ls]() {
+        step = Step::ThreadStarted;
+
+        WAIT_FOR(step == Step::BeforeUsleep);
+
+        step = Step::UsleepNotTriggeredYet;
+        ls.set_absolute_time(some_time_us + 500);
+
+        step = Step::UsleepTriggered;
+        ls.set_absolute_time(some_time_us + 1500);
+    });
+
+    WAIT_FOR(step == Step::ThreadStarted);
+
+    step = Step::BeforeUsleep;
+
+    assert(ls.usleep_until(some_time_us + 1000) == 0);
+    assert(step == Step::UsleepTriggered);
+    thread.join();
+}
+
+int main(int /*argc*/, char** /*argv*/)
+{
+    for (unsigned iteration = 1; iteration <= 10000; ++iteration) {
+        std::cout << "Test iteration: " << iteration << "\n";
+        test_absolute_time();
+        test_condition_timing_out();
+        test_locked_semaphore_getting_unlocked();
+        test_usleep();
+        test_multiple_semaphores_waiting();
+    }
+
+    return 0;
+}