| // Copyright 2020 The Pigweed Authors |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); you may not |
| // use this file except in compliance with the License. You may obtain a copy of |
| // the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT |
| // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the |
| // License for the specific language governing permissions and limitations under |
| // the License. |
| |
| #include "pw_chrono/system_clock.h" |
| |
| #include <atomic> |
| #include <chrono> |
| #include <limits> |
| #include <mutex> |
| |
| #include "FreeRTOS.h" |
| #include "pw_interrupt/context.h" |
| #include "pw_sync/spin_lock.h" |
| #include "task.h" |
| |
| namespace pw::chrono::backend { |
| namespace { |
| |
| // Extension wrapping pw::SpinLock to allow an atomic to be used to determine |
| // whether it has been constructed and is ready to be used. |
| class ConstructionSignalingSpinLock : public sync::SpinLock { |
| public: |
| ConstructionSignalingSpinLock(std::atomic<bool>& constructed_signal) |
| : sync::SpinLock() { |
| // Note that the memory order is relaxed because C++ global static |
| // construction is a single threaded environment. |
| constructed_signal.store(true, std::memory_order_relaxed); |
| }; |
| }; |
| |
| // This is POD, meaning this atomic is available before static C++ global |
| // constructors are run. |
| std::atomic<bool> system_clock_spin_lock_constructed = {false}; |
| |
| ConstructionSignalingSpinLock system_clock_spin_lock( |
| system_clock_spin_lock_constructed); |
| |
| int64_t overflow_tick_count = 0; |
| TickType_t native_tick_count = 0; |
| static_assert(!SystemClock::is_nmi_safe, |
| "global state is not atomic nor double buferred"); |
| |
| // The tick count resets to 0, ergo the overflow count is the max count + 1. |
| constexpr int64_t kNativeOverflowTickCount = |
| static_cast<int64_t>(std::numeric_limits<TickType_t>::max()) + 1; |
| |
| } // namespace |
| |
| int64_t GetSystemClockTickCount() { |
| // Note that the memory order is relaxed because C++ global static |
| // construction is a single threaded environment. |
| if (!system_clock_spin_lock_constructed.load(std::memory_order_relaxed)) { |
| return interrupt::InInterruptContext() ? xTaskGetTickCountFromISR() |
| : xTaskGetTickCount(); |
| } |
| |
| std::lock_guard lock(system_clock_spin_lock); |
| const TickType_t new_native_tick_count = interrupt::InInterruptContext() |
| ? xTaskGetTickCountFromISR() |
| : xTaskGetTickCount(); |
| // WARNING: This must be called more than once per overflow period! |
| if (new_native_tick_count < native_tick_count) { |
| // Native tick count overflow detected! |
| overflow_tick_count += kNativeOverflowTickCount; |
| } |
| native_tick_count = new_native_tick_count; |
| return overflow_tick_count + native_tick_count; |
| } |
| |
| } // namespace pw::chrono::backend |