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 "pw_assert/check.h"
20 #include "pw_chrono/system_clock.h"
21 #include "pw_chrono_threadx/system_clock_constants.h"
22 #include "pw_interrupt/context.h"
23 #include "tx_api.h"
24
25 using pw::chrono::SystemClock;
26
27 namespace pw::sync {
28
try_acquire_for(SystemClock::duration timeout)29 bool BinarySemaphore::try_acquire_for(SystemClock::duration timeout) {
30 // Enforce the pw::sync::BinarySemaphore IRQ contract.
31 PW_DCHECK(!interrupt::InInterruptContext());
32
33 // Use non-blocking try_acquire for negative and zero length durations.
34 if (timeout <= SystemClock::duration::zero()) {
35 return try_acquire();
36 }
37
38 // In case the timeout is too long for us to express through the native
39 // ThreadX API, we repeatedly wait with shorter durations. Note that on a tick
40 // based kernel we cannot tell how far along we are on the current tick, ergo
41 // we add one whole tick to the final duration. However, this also means that
42 // the loop must ensure that timeout + 1 is less than the max timeout.
43 constexpr SystemClock::duration kMaxTimeoutMinusOne =
44 pw::chrono::threadx::kMaxTimeout - SystemClock::duration(1);
45 while (timeout > kMaxTimeoutMinusOne) {
46 const UINT result = tx_semaphore_get(
47 &native_type_, static_cast<ULONG>(kMaxTimeoutMinusOne.count()));
48 if (result != TX_NO_INSTANCE) {
49 // If we didn't time out (TX_NO_INSTANCE), then we should have succeeded.
50 PW_CHECK_UINT_EQ(TX_SUCCESS, result);
51 return true;
52 }
53 timeout -= kMaxTimeoutMinusOne;
54 }
55 // On a tick based kernel we cannot tell how far along we are on the current
56 // tick, ergo we add one whole tick to the final duration.
57 const UINT result =
58 tx_semaphore_get(&native_type_, static_cast<ULONG>(timeout.count() + 1));
59 if (result == TX_NO_INSTANCE) {
60 return false; // We timed out, there's still no token.
61 }
62 PW_CHECK_UINT_EQ(TX_SUCCESS, result);
63 return true;
64 }
65
66 } // namespace pw::sync
67