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/counting_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(configUSE_COUNTING_SEMAPHORES != 0,
32 "FreeRTOS counting semaphores aren't enabled.");
33
34 static_assert(configSUPPORT_STATIC_ALLOCATION != 0,
35 "FreeRTOS static allocations are required for this backend.");
36
37 } // namespace
38
release(ptrdiff_t update)39 void CountingSemaphore::release(ptrdiff_t update) {
40 if (interrupt::InInterruptContext()) {
41 for (; update > 0; --update) {
42 BaseType_t woke_higher_task = pdFALSE;
43 const BaseType_t result = xSemaphoreGiveFromISR(
44 reinterpret_cast<SemaphoreHandle_t>(&native_type_),
45 &woke_higher_task);
46 PW_DCHECK_UINT_EQ(result, pdTRUE, "Overflowed counting semaphore.");
47 portYIELD_FROM_ISR(woke_higher_task);
48 }
49 } else { // Task context
50 for (; update > 0; --update) {
51 const BaseType_t result =
52 xSemaphoreGive(reinterpret_cast<SemaphoreHandle_t>(&native_type_));
53 PW_DCHECK_UINT_EQ(result, pdTRUE, "Overflowed counting semaphore.");
54 }
55 }
56 }
57
try_acquire_for(SystemClock::duration timeout)58 bool CountingSemaphore::try_acquire_for(SystemClock::duration timeout) {
59 // Enforce the pw::sync::CountingSemaphore IRQ contract.
60 PW_DCHECK(!interrupt::InInterruptContext());
61
62 // Use non-blocking try_acquire for negative and zero length durations.
63 if (timeout <= SystemClock::duration::zero()) {
64 return try_acquire();
65 }
66
67 // In case the timeout is too long for us to express through the native
68 // FreeRTOS API, we repeatedly wait with shorter durations. Note that on a
69 // tick based kernel we cannot tell how far along we are on the current tick,
70 // ergo we add one whole tick to the final duration. However, this also means
71 // that the loop must ensure that timeout + 1 is less than the max timeout.
72 constexpr SystemClock::duration kMaxTimeoutMinusOne =
73 pw::chrono::freertos::kMaxTimeout - SystemClock::duration(1);
74 while (timeout > kMaxTimeoutMinusOne) {
75 if (xSemaphoreTake(reinterpret_cast<SemaphoreHandle_t>(&native_type_),
76 static_cast<TickType_t>(kMaxTimeoutMinusOne.count())) ==
77 pdTRUE) {
78 return true;
79 }
80 timeout -= kMaxTimeoutMinusOne;
81 }
82 // On a tick based kernel we cannot tell how far along we are on the current
83 // tick, ergo we add one whole tick to the final duration.
84 return xSemaphoreTake(reinterpret_cast<SemaphoreHandle_t>(&native_type_),
85 static_cast<TickType_t>(timeout.count() + 1)) == pdTRUE;
86 }
87
88 } // namespace pw::sync
89