Ewout van Bekkum | 666935d | 2021-06-21 15:52:50 -0700 | [diff] [blame] | 1 | // Copyright 2021 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_timer.h" |
| 16 | |
| 17 | #include <mutex> |
| 18 | |
| 19 | #include "RTOS.h" |
| 20 | #include "pw_assert/check.h" |
| 21 | #include "pw_chrono_embos/system_clock_constants.h" |
| 22 | #include "pw_interrupt/context.h" |
| 23 | |
| 24 | namespace pw::chrono { |
| 25 | namespace { |
| 26 | |
| 27 | // Instead of adding targeted locks to each instance, simply use the global |
| 28 | // recursive critical section lock. Note it has to be recursive because a timer |
| 29 | // cannot be started with a time period of 0 and ergo the Invoke* API might |
| 30 | // have to directly invoke the callback. |
| 31 | class RecursiveCriticalSectionLock { |
| 32 | public: |
| 33 | void lock() { |
| 34 | OS_IncDI(); // Mask interrupts. |
| 35 | OS_SuspendAllTasks(); // Disable task switching. |
| 36 | } |
| 37 | |
| 38 | void unlock() { |
| 39 | OS_ResumeAllSuspendedTasks(); // Restore task switching. |
| 40 | OS_DecRI(); // Restore interrupts. |
| 41 | } |
| 42 | }; |
| 43 | RecursiveCriticalSectionLock recursive_global_timer_lock; |
| 44 | |
| 45 | void HandleTimerCallback(void* void_native_system_timer) { |
| 46 | // NOTE: embOS invokes all timer callbacks from a single interrupt. Ergo we do |
| 47 | // not add a unnecessary grab of the recursive_global_timer_lock here. |
| 48 | PW_DCHECK(interrupt::InInterruptContext(), |
| 49 | "HandleTimerCallback must be invoked from an interrupt"); |
| 50 | // TODO(ewout): can we potentially skip this as it's always in an interrupt |
| 51 | // handler and the control API is not interrupt safe? |
| 52 | std::lock_guard lock(recursive_global_timer_lock); |
| 53 | |
| 54 | backend::NativeSystemTimer& native_type = |
| 55 | *static_cast<backend::NativeSystemTimer*>(void_native_system_timer); |
| 56 | const SystemClock::duration time_until_deadline = |
| 57 | native_type.expiry_deadline - SystemClock::now(); |
| 58 | if (time_until_deadline <= SystemClock::duration::zero()) { |
| 59 | // We have met the deadline, execute the user's callback. |
| 60 | native_type.user_callback(native_type.expiry_deadline); |
| 61 | return; |
| 62 | } |
| 63 | const SystemClock::duration period = |
| 64 | std::min(pw::chrono::embos::kMaxTimeout, time_until_deadline); |
| 65 | OS_SetTimerPeriodEx(&native_type.tcb, static_cast<OS_TIME>(period.count())); |
| 66 | OS_StartTimerEx(&native_type.tcb); |
| 67 | } |
| 68 | |
| 69 | constexpr OS_TIME kInvalidPeriod = 0; |
| 70 | |
| 71 | } // namespace |
| 72 | |
| 73 | SystemTimer::SystemTimer(ExpiryCallback callback) |
| 74 | : native_type_{.tcb{}, |
| 75 | .expiry_deadline = SystemClock::time_point(), |
| 76 | .user_callback = std::move(callback)} { |
| 77 | OS_CreateTimerEx( |
| 78 | &native_type_.tcb, HandleTimerCallback, kInvalidPeriod, &native_type_); |
| 79 | } |
| 80 | |
| 81 | SystemTimer::~SystemTimer() { |
| 82 | // Not threadsafe by design. |
| 83 | Cancel(); |
| 84 | OS_DeleteTimerEx(&native_type_.tcb); |
| 85 | } |
| 86 | |
| 87 | void SystemTimer::InvokeAt(SystemClock::time_point timestamp) { |
| 88 | std::lock_guard lock(recursive_global_timer_lock); |
| 89 | |
| 90 | // Ensure the timer has been cancelled first. |
| 91 | Cancel(); |
| 92 | |
| 93 | native_type_.expiry_deadline = timestamp; |
| 94 | const SystemClock::duration time_until_deadline = |
| 95 | timestamp - SystemClock::now(); |
| 96 | |
| 97 | // Timers can only be created with a non-zero period, ergo we must immediately |
| 98 | // invoke the user's callback if it cannot be deferred by at least a partial |
| 99 | // tick. |
| 100 | if (time_until_deadline <= SystemClock::duration::zero()) { |
| 101 | native_type_.user_callback(timestamp); |
| 102 | return; |
| 103 | } |
| 104 | |
| 105 | // Schedule the timer as far out as possible. Note that the timeout might be |
| 106 | // clamped and it may be rescheduled internally. |
| 107 | const SystemClock::duration period = |
| 108 | std::min(pw::chrono::embos::kMaxTimeout, time_until_deadline); |
| 109 | OS_SetTimerPeriodEx(&native_type_.tcb, static_cast<OS_TIME>(period.count())); |
| 110 | OS_RetriggerTimerEx(&native_type_.tcb); |
| 111 | } |
| 112 | |
| 113 | } // namespace pw::chrono |