mbed_poll.cpp

00001 /* mbed Microcontroller Library
00002  * Copyright (c) 2017 ARM Limited
00003  *
00004  * Licensed under the Apache License, Version 2.0 (the "License");
00005  * you may not use this file except in compliance with the License.
00006  * You may obtain a copy of the License at
00007  *
00008  *     http://www.apache.org/licenses/LICENSE-2.0
00009  *
00010  * Unless required by applicable law or agreed to in writing, software
00011  * distributed under the License is distributed on an "AS IS" BASIS,
00012  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00013  * See the License for the specific language governing permissions and
00014  * limitations under the License.
00015  */
00016 #include "mbed_poll.h"
00017 #include "FileHandle.h"
00018 #if MBED_CONF_RTOS_PRESENT
00019 #include "rtos/Kernel.h"
00020 #include "rtos/Thread.h"
00021 using namespace rtos;
00022 #else
00023 #include "Timer.h"
00024 #include "LowPowerTimer.h"
00025 #endif
00026 
00027 namespace mbed {
00028 
00029 // timeout -1 forever, or milliseconds
00030 int poll(pollfh fhs[], unsigned nfhs, int timeout)
00031 {
00032     /**
00033      * TODO Proper wake-up mechanism.
00034      * In order to correctly detect availability of read/write a FileHandle, we needed
00035      * a select or poll mechanisms. We opted for poll as POSIX defines in
00036      * http://pubs.opengroup.org/onlinepubs/009695399/functions/poll.html Currently,
00037      * mbed::poll() just spins and scans filehandles looking for any events we are
00038      * interested in. In future, his spinning behaviour will be replaced with
00039      * condition variables.
00040      */
00041 #if MBED_CONF_RTOS_PRESENT
00042     uint64_t start_time = 0;
00043     if (timeout > 0) {
00044         start_time = Kernel::get_ms_count();
00045     }
00046 #define TIME_ELAPSED() int64_t(Kernel::get_ms_count() - start_time)
00047 #else
00048 #if MBED_CONF_PLATFORM_POLL_USE_LOWPOWER_TIMER
00049     LowPowerTimer timer;
00050 #else
00051     Timer timer;
00052 #endif
00053     if (timeout > 0) {
00054         timer.start();
00055     }
00056 #define TIME_ELAPSED() timer.read_ms()
00057 #endif // MBED_CONF_RTOS_PRESENT
00058 
00059     int count = 0;
00060     for (;;) {
00061         /* Scan the file handles */
00062         for (unsigned n = 0; n < nfhs; n++) {
00063             FileHandle *fh = fhs[n].fh;
00064             short mask = fhs[n].events | POLLERR | POLLHUP | POLLNVAL;
00065             if (fh) {
00066                 fhs[n].revents = fh->poll(mask) & mask;
00067             } else {
00068                 fhs[n].revents = POLLNVAL;
00069             }
00070             if (fhs[n].revents) {
00071                 count++;
00072             }
00073         }
00074 
00075         if (count) {
00076             break;
00077         }
00078 
00079         /* Nothing selected - this is where timeout handling would be needed */
00080         if (timeout == 0 || (timeout > 0 && TIME_ELAPSED() > timeout)) {
00081             break;
00082         }
00083 #ifdef MBED_CONF_RTOS_PRESENT
00084         // TODO - proper blocking
00085         // wait for condition variable, wait queue whatever here
00086         rtos::Thread::wait(1);
00087 #endif
00088     }
00089     return count;
00090 }
00091 
00092 } // namespace mbed