MonoPipe.cpp revision 2dd4bdd715f586d4d30cf90cc6fc2bbfbce60fe0 
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 "MonoPipe"
18//#define LOG_NDEBUG 0
19
20#include <common_time/cc_helper.h>
21#include <cutils/atomic.h>
22#include <cutils/compiler.h>
23#include <utils/LinearTransform.h>
24#include <utils/Log.h>
25#include <utils/Trace.h>
26#include <media/AudioBufferProvider.h>
27#include <media/nbaio/MonoPipe.h>
28#include <media/nbaio/roundup.h>
29
30
31namespace android {
32
33MonoPipe::MonoPipe(size_t reqFrames, NBAIO_Format format, bool writeCanBlock) :
34        NBAIO_Sink(format),
35        mUpdateSeq(0),
36        mReqFrames(reqFrames),
37        mMaxFrames(roundup(reqFrames)),
38        mBuffer(malloc(mMaxFrames * Format_frameSize(format))),
39        mFront(0),
40        mRear(0),
41        mWriteTsValid(false),
42        // mWriteTs
43        mSetpoint((reqFrames * 11) / 16),
44        mWriteCanBlock(writeCanBlock)
45{
46    CCHelper tmpHelper;
47    status_t res;
48    uint64_t N, D;
49
50    mNextRdPTS = AudioBufferProvider::kInvalidPTS;
51
52    mSamplesToLocalTime.a_zero = 0;
53    mSamplesToLocalTime.b_zero = 0;
54    mSamplesToLocalTime.a_to_b_numer = 0;
55    mSamplesToLocalTime.a_to_b_denom = 0;
56
57    D = Format_sampleRate(format);
58    if (OK != (res = tmpHelper.getLocalFreq(&N))) {
59        ALOGE("Failed to fetch local time frequency when constructing a"
60              " MonoPipe (res = %d).  getNextWriteTimestamp calls will be"
61              " non-functional", res);
62        return;
63    }
64
65    LinearTransform::reduce(&N, &D);
66    static const uint64_t kSignedHiBitsMask   = ~(0x7FFFFFFFull);
67    static const uint64_t kUnsignedHiBitsMask = ~(0xFFFFFFFFull);
68    if ((N & kSignedHiBitsMask) || (D & kUnsignedHiBitsMask)) {
69        ALOGE("Cannot reduce sample rate to local clock frequency ratio to fit"
70              " in a 32/32 bit rational.  (max reduction is 0x%016llx/0x%016llx"
71              ").  getNextWriteTimestamp calls will be non-functional", N, D);
72        return;
73    }
74
75    mSamplesToLocalTime.a_to_b_numer = static_cast<int32_t>(N);
76    mSamplesToLocalTime.a_to_b_denom = static_cast<uint32_t>(D);
77}
78
79MonoPipe::~MonoPipe()
80{
81    free(mBuffer);
82}
83
84ssize_t MonoPipe::availableToWrite() const
85{
86    if (CC_UNLIKELY(!mNegotiated)) {
87        return NEGOTIATE;
88    }
89    // uses mMaxFrames not mReqFrames, so allows "over-filling" the pipe beyond requested limit
90    ssize_t ret = mMaxFrames - (mRear - android_atomic_acquire_load(&mFront));
91    ALOG_ASSERT((0 <= ret) && (ret <= mMaxFrames));
92    return ret;
93}
94
95ssize_t MonoPipe::write(const void *buffer, size_t count)
96{
97    if (CC_UNLIKELY(!mNegotiated)) {
98        return NEGOTIATE;
99    }
100    size_t totalFramesWritten = 0;
101    while (count > 0) {
102        // can't return a negative value, as we already checked for !mNegotiated
103        size_t avail = availableToWrite();
104        size_t written = avail;
105        if (CC_LIKELY(written > count)) {
106            written = count;
107        }
108        size_t rear = mRear & (mMaxFrames - 1);
109        size_t part1 = mMaxFrames - rear;
110        if (part1 > written) {
111            part1 = written;
112        }
113        if (CC_LIKELY(part1 > 0)) {
114            memcpy((char *) mBuffer + (rear << mBitShift), buffer, part1 << mBitShift);
115            if (CC_UNLIKELY(rear + part1 == mMaxFrames)) {
116                size_t part2 = written - part1;
117                if (CC_LIKELY(part2 > 0)) {
118                    memcpy(mBuffer, (char *) buffer + (part1 << mBitShift), part2 << mBitShift);
119                }
120            }
121            android_atomic_release_store(written + mRear, &mRear);
122            totalFramesWritten += written;
123        }
124        if (!mWriteCanBlock) {
125            break;
126        }
127        count -= written;
128        buffer = (char *) buffer + (written << mBitShift);
129        // Simulate blocking I/O by sleeping at different rates, depending on a throttle.
130        // The throttle tries to keep the mean pipe depth near the setpoint, with a slight jitter.
131        uint32_t ns;
132        if (written > 0) {
133            size_t filled = (mMaxFrames - avail) + written;
134            // FIXME cache these values to avoid re-computation
135            if (filled <= mSetpoint / 2) {
136                // pipe is (nearly) empty, fill quickly
137                ns = written * ( 500000000 / Format_sampleRate(mFormat));
138            } else if (filled <= (mSetpoint * 3) / 4) {
139                // pipe is below setpoint, fill at slightly faster rate
140                ns = written * ( 750000000 / Format_sampleRate(mFormat));
141            } else if (filled <= (mSetpoint * 5) / 4) {
142                // pipe is at setpoint, fill at nominal rate
143                ns = written * (1000000000 / Format_sampleRate(mFormat));
144            } else if (filled <= (mSetpoint * 3) / 2) {
145                // pipe is above setpoint, fill at slightly slower rate
146                ns = written * (1150000000 / Format_sampleRate(mFormat));
147            } else if (filled <= (mSetpoint * 7) / 4) {
148                // pipe is overflowing, fill slowly
149                ns = written * (1350000000 / Format_sampleRate(mFormat));
150            } else {
151                // pipe is severely overflowing
152                ns = written * (1750000000 / Format_sampleRate(mFormat));
153            }
154        } else {
155            ns = count * (1350000000 / Format_sampleRate(mFormat));
156        }
157        if (ns > 999999999) {
158            ns = 999999999;
159        }
160        struct timespec nowTs;
161        bool nowTsValid = !clock_gettime(CLOCK_MONOTONIC, &nowTs);
162        // deduct the elapsed time since previous write() completed
163        if (nowTsValid && mWriteTsValid) {
164            time_t sec = nowTs.tv_sec - mWriteTs.tv_sec;
165            long nsec = nowTs.tv_nsec - mWriteTs.tv_nsec;
166            if (nsec < 0) {
167                --sec;
168                nsec += 1000000000;
169            }
170            if (sec == 0) {
171                if ((long) ns > nsec) {
172                    ns -= nsec;
173                } else {
174                    ns = 0;
175                }
176            }
177        }
178        if (ns > 0) {
179            const struct timespec req = {0, ns};
180            nanosleep(&req, NULL);
181        }
182        // record the time that this write() completed
183        if (nowTsValid) {
184            mWriteTs = nowTs;
185            if ((mWriteTs.tv_nsec += ns) >= 1000000000) {
186                mWriteTs.tv_nsec -= 1000000000;
187                ++mWriteTs.tv_sec;
188            }
189        }
190        mWriteTsValid = nowTsValid;
191    }
192    mFramesWritten += totalFramesWritten;
193    return totalFramesWritten;
194}
195
196void MonoPipe::setAvgFrames(size_t setpoint)
197{
198    mSetpoint = setpoint;
199}
200
201status_t MonoPipe::getNextWriteTimestamp(int64_t *timestamp)
202{
203    int32_t front;
204
205    ALOG_ASSERT(NULL != timestamp);
206
207    if (0 == mSamplesToLocalTime.a_to_b_denom)
208        return UNKNOWN_ERROR;
209
210    observeFrontAndNRPTS(&front, timestamp);
211
212    if (AudioBufferProvider::kInvalidPTS != *timestamp) {
213        // If we have a valid read-pointer and next read timestamp pair, then
214        // use the current value of the write pointer to figure out how many
215        // frames are in the buffer, and offset the timestamp by that amt.  Then
216        // next time we write to the MonoPipe, the data will hit the speakers at
217        // the next read timestamp plus the current amount of data in the
218        // MonoPipe.
219        size_t pendingFrames = (mRear - front) & (mMaxFrames - 1);
220        *timestamp = offsetTimestampByAudioFrames(*timestamp, pendingFrames);
221    }
222
223    return OK;
224}
225
226void MonoPipe::updateFrontAndNRPTS(int32_t newFront, int64_t newNextRdPTS)
227{
228    // Set the MSB of the update sequence number to indicate that there is a
229    // multi-variable update in progress.  Use an atomic store with an "acquire"
230    // barrier to make sure that the next operations cannot be re-ordered and
231    // take place before the change to mUpdateSeq is commited..
232    int32_t tmp = mUpdateSeq | 0x80000000;
233    android_atomic_acquire_store(tmp, &mUpdateSeq);
234
235    // Update mFront and mNextRdPTS
236    mFront = newFront;
237    mNextRdPTS = newNextRdPTS;
238
239    // We are finished with the update.  Compute the next sequnce number (which
240    // should be the old sequence number, plus one, and with the MSB cleared)
241    // and then store it in mUpdateSeq using an atomic store with a "release"
242    // barrier so our update operations cannot be re-ordered past the update of
243    // the sequence number.
244    tmp = (tmp + 1) & 0x7FFFFFFF;
245    android_atomic_release_store(tmp, &mUpdateSeq);
246}
247
248void MonoPipe::observeFrontAndNRPTS(int32_t *outFront, int64_t *outNextRdPTS)
249{
250    // Perform an atomic observation of mFront and mNextRdPTS.  Basically,
251    // atomically observe the sequence number, then observer the variables, then
252    // atomically observe the sequence number again.  If the two observations of
253    // the sequence number match, and the update-in-progress bit was not set,
254    // then we know we have a successful atomic observation.  Otherwise, we loop
255    // around and try again.
256    //
257    // Note, it is very important that the observer be a lower priority thread
258    // than the updater.  If the updater is lower than the observer, or they are
259    // the same priority and running with SCHED_FIFO (implying that quantum
260    // based premption is disabled) then we run the risk of deadlock.
261    int32_t seqOne, seqTwo;
262
263    do {
264        seqOne        = android_atomic_acquire_load(&mUpdateSeq);
265        *outFront     = mFront;
266        *outNextRdPTS = mNextRdPTS;
267        seqTwo        = android_atomic_release_load(&mUpdateSeq);
268    } while ((seqOne != seqTwo) || (seqOne & 0x80000000));
269}
270
271int64_t MonoPipe::offsetTimestampByAudioFrames(int64_t ts, size_t audFrames)
272{
273    if (0 == mSamplesToLocalTime.a_to_b_denom)
274        return AudioBufferProvider::kInvalidPTS;
275
276    if (ts == AudioBufferProvider::kInvalidPTS)
277        return AudioBufferProvider::kInvalidPTS;
278
279    int64_t frame_lt_duration;
280    if (!mSamplesToLocalTime.doForwardTransform(audFrames,
281                                                &frame_lt_duration)) {
282        // This should never fail, but if there is a bug which is causing it
283        // to fail, this message would probably end up flooding the logs
284        // because the conversion would probably fail forever.  Log the
285        // error, but then zero out the ratio in the linear transform so
286        // that we don't try to do any conversions from now on.  This
287        // MonoPipe's getNextWriteTimestamp is now broken for good.
288        ALOGE("Overflow when attempting to convert %d audio frames to"
289              " duration in local time.  getNextWriteTimestamp will fail from"
290              " now on.", audFrames);
291        mSamplesToLocalTime.a_to_b_numer = 0;
292        mSamplesToLocalTime.a_to_b_denom = 0;
293        return AudioBufferProvider::kInvalidPTS;
294    }
295
296    return ts + frame_lt_duration;
297}
298
299}   // namespace android
300