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63 lines
2.1 KiB
63 lines
2.1 KiB
4 months ago
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// Copyright 2021 The Pigweed Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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#include "pw_chrono/system_clock.h"
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#include <atomic>
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#include <chrono>
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#include <limits>
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#include <mutex>
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#include "RTOS.h"
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#include "pw_sync/interrupt_spin_lock.h"
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namespace pw::chrono::backend {
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namespace {
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sync::InterruptSpinLock system_clock_interrupt_spin_lock;
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int64_t overflow_tick_count = 0;
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uint32_t native_tick_count = 0;
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static_assert(!SystemClock::is_nmi_safe,
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"global state is not atomic nor double buferred");
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static_assert(sizeof(void*) == 4, "this backend only supports 32 bit targets!");
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inline uint32_t GetUint32TickCount() {
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// embOS returns a signed 32 bit value, however according to their developers
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// the binary value continues to increment like an unsigned value, ergo we
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// instead reinterpret the tick count as the raw underlying 32 bit unsigned
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// tick count.
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return static_cast<uint32_t>(OS_GetTime32());
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}
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// The tick count resets to 0, ergo the overflow count is the max count + 1.
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constexpr int64_t kNativeOverflowTickCount =
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static_cast<int64_t>(std::numeric_limits<uint32_t>::max()) + 1;
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} // namespace
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int64_t GetSystemClockTickCount() {
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std::lock_guard lock(system_clock_interrupt_spin_lock);
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const uint32_t new_native_tick_count = GetUint32TickCount();
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// WARNING: This must be called more than once per overflow period!
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if (new_native_tick_count < native_tick_count) {
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// Native tick count overflow detected!
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overflow_tick_count += kNativeOverflowTickCount;
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}
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native_tick_count = new_native_tick_count;
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return overflow_tick_count + native_tick_count;
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}
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} // namespace pw::chrono::backend
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