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_sync/binary_semaphore.h"
16
17 #include <algorithm>
18
19 #include "FreeRTOS.h"
20 #include "pw_assert/check.h"
21 #include "pw_chrono/system_clock.h"
22 #include "pw_chrono_freertos/system_clock_constants.h"
23 #include "pw_interrupt/context.h"
24 #include "semphr.h"
25
26 using pw::chrono::SystemClock;
27
28 namespace pw::sync {
29 namespace {
30
31 static_assert(configSUPPORT_STATIC_ALLOCATION != 0,
32 "FreeRTOS static allocations are required for this backend.");
33
34 } // namespace
35
try_acquire_for(SystemClock::duration timeout)36 bool BinarySemaphore::try_acquire_for(SystemClock::duration timeout) {
37 // Enforce the pw::sync::BinarySemaphore IRQ contract.
38 PW_DCHECK(!interrupt::InInterruptContext());
39
40 // Use non-blocking try_acquire for negative and zero length durations.
41 if (timeout <= SystemClock::duration::zero()) {
42 return try_acquire();
43 }
44
45 // In case the timeout is too long for us to express through the native
46 // FreeRTOS API, we repeatedly wait with shorter durations. Note that on a
47 // tick based kernel we cannot tell how far along we are on the current tick,
48 // ergo we add one whole tick to the final duration. However, this also means
49 // that the loop must ensure that timeout + 1 is less than the max timeout.
50 constexpr SystemClock::duration kMaxTimeoutMinusOne =
51 pw::chrono::freertos::kMaxTimeout - SystemClock::duration(1);
52 while (timeout > kMaxTimeoutMinusOne) {
53 if (xSemaphoreTake(reinterpret_cast<SemaphoreHandle_t>(&native_type_),
54 static_cast<TickType_t>(kMaxTimeoutMinusOne.count())) ==
55 pdTRUE) {
56 return true;
57 }
58 timeout -= kMaxTimeoutMinusOne;
59 }
60 // On a tick based kernel we cannot tell how far along we are on the current
61 // tick, ergo we add one whole tick to the final duration.
62 return xSemaphoreTake(reinterpret_cast<SemaphoreHandle_t>(&native_type_),
63 static_cast<TickType_t>(timeout.count() + 1)) == pdTRUE;
64 }
65
66 } // namespace pw::sync
67