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      1 /*
      2  * Copyright (C) 2012 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #define LOG_TAG "MonoPipeReader"
     18 //#define LOG_NDEBUG 0
     19 
     20 #include <cutils/compiler.h>
     21 #include <utils/Log.h>
     22 #include <media/nbaio/MonoPipeReader.h>
     23 
     24 namespace android {
     25 
     26 MonoPipeReader::MonoPipeReader(MonoPipe* pipe) :
     27         NBAIO_Source(pipe->mFormat),
     28         mPipe(pipe)
     29 {
     30 }
     31 
     32 MonoPipeReader::~MonoPipeReader()
     33 {
     34 }
     35 
     36 ssize_t MonoPipeReader::availableToRead()
     37 {
     38     if (CC_UNLIKELY(!mNegotiated)) {
     39         return NEGOTIATE;
     40     }
     41     ssize_t ret = android_atomic_acquire_load(&mPipe->mRear) - mPipe->mFront;
     42     ALOG_ASSERT((0 <= ret) && (ret <= mMaxFrames));
     43     return ret;
     44 }
     45 
     46 ssize_t MonoPipeReader::read(void *buffer, size_t count, int64_t readPTS)
     47 {
     48     // Compute the "next read PTS" and cache it.  Callers of read pass a read
     49     // PTS indicating the local time for which they are requesting data along
     50     // with a count (which is the number of audio frames they are going to
     51     // ultimately pass to the next stage of the pipeline).  Offsetting readPTS
     52     // by the duration of count will give us the readPTS which will be passed to
     53     // us next time, assuming they system continues to operate in steady state
     54     // with no discontinuities.  We stash this value so it can be used by the
     55     // MonoPipe writer to imlement getNextWriteTimestamp.
     56     int64_t nextReadPTS;
     57     nextReadPTS = mPipe->offsetTimestampByAudioFrames(readPTS, count);
     58 
     59     // count == 0 is unlikely and not worth checking for explicitly; will be handled automatically
     60     ssize_t red = availableToRead();
     61     if (CC_UNLIKELY(red <= 0)) {
     62         // Uh-oh, looks like we are underflowing.  Update the next read PTS and
     63         // get out.
     64         mPipe->updateFrontAndNRPTS(mPipe->mFront, nextReadPTS);
     65         return red;
     66     }
     67     if (CC_LIKELY((size_t) red > count)) {
     68         red = count;
     69     }
     70     size_t front = mPipe->mFront & (mPipe->mMaxFrames - 1);
     71     size_t part1 = mPipe->mMaxFrames - front;
     72     if (part1 > (size_t) red) {
     73         part1 = red;
     74     }
     75     if (CC_LIKELY(part1 > 0)) {
     76         memcpy(buffer, (char *) mPipe->mBuffer + (front << mBitShift), part1 << mBitShift);
     77         if (CC_UNLIKELY(front + part1 == mPipe->mMaxFrames)) {
     78             size_t part2 = red - part1;
     79             if (CC_LIKELY(part2 > 0)) {
     80                 memcpy((char *) buffer + (part1 << mBitShift), mPipe->mBuffer, part2 << mBitShift);
     81             }
     82         }
     83         mPipe->updateFrontAndNRPTS(red + mPipe->mFront, nextReadPTS);
     84         mFramesRead += red;
     85     }
     86     return red;
     87 }
     88 
     89 }   // namespace android
     90