1 // Copyright 2020 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 //     https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14 
15 #include "pw_chrono/system_clock.h"
16 
17 #include <atomic>
18 #include <chrono>
19 #include <limits>
20 #include <mutex>
21 
22 #include "FreeRTOS.h"
23 #include "pw_interrupt/context.h"
24 #include "pw_sync/interrupt_spin_lock.h"
25 #include "task.h"
26 
27 namespace pw::chrono::backend {
28 namespace {
29 
30 sync::InterruptSpinLock system_clock_interrupt_spin_lock;
31 int64_t overflow_tick_count = 0;
32 TickType_t native_tick_count = 0;
33 static_assert(!SystemClock::is_nmi_safe,
34               "global state is not atomic nor double buferred");
35 
36 // The tick count resets to 0, ergo the overflow count is the max count + 1.
37 constexpr int64_t kNativeOverflowTickCount =
38     static_cast<int64_t>(std::numeric_limits<TickType_t>::max()) + 1;
39 
40 }  // namespace
41 
GetSystemClockTickCount()42 int64_t GetSystemClockTickCount() {
43   std::lock_guard lock(system_clock_interrupt_spin_lock);
44   const TickType_t new_native_tick_count = interrupt::InInterruptContext()
45                                                ? xTaskGetTickCountFromISR()
46                                                : xTaskGetTickCount();
47   // WARNING: This must be called more than once per overflow period!
48   if (new_native_tick_count < native_tick_count) {
49     // Native tick count overflow detected!
50     overflow_tick_count += kNativeOverflowTickCount;
51   }
52   native_tick_count = new_native_tick_count;
53   return overflow_tick_count + native_tick_count;
54 }
55 
56 }  // namespace pw::chrono::backend
57