| // 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 "pw_sync/interrupt_spin_lock.h" |
| #include "tx_api.h" |
| |
| namespace pw::chrono::backend { |
| namespace { |
| |
| #if defined(TX_NO_TIMER) && TX_NO_TIMER |
| #error "This backend is not compatible with TX_NO_TIMER" |
| #endif // defined(TX_NO_TIMER) && TX_NO_TIMER |
| |
| sync::InterruptSpinLock system_clock_interrupt_spin_lock; |
| int64_t overflow_tick_count = 0; |
| ULONG 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<ULONG>::max()) + 1; |
| |
| } // namespace |
| |
| int64_t GetSystemClockTickCount() { |
| std::lock_guard lock(system_clock_interrupt_spin_lock); |
| const ULONG new_native_tick_count = tx_time_get(); |
| // 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 |