/*
* Copyright (C) 2012 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ANDROID_AUDIO_NBAIO_H
#define ANDROID_AUDIO_NBAIO_H
// Non-blocking audio I/O interface
//
// This header file has the abstract interfaces only. Concrete implementation classes are declared
// elsewhere. Implementations _should_ be non-blocking for all methods, especially read() and
// write(), but this is not enforced. In general, implementations do not need to be multi-thread
// safe, and any exceptions are noted in the particular implementation.
#include <limits.h>
#include <stdlib.h>
#include <utils/RefBase.h>
namespace android {
// In addition to the usual status_t
enum {
NEGOTIATE = 0x80000010, // Must (re-)negotiate format. For negotiate() only, the offeree
// doesn't accept offers, and proposes counter-offers
OVERRUN = 0x80000011, // availableToRead(), read(), or readVia() detected lost input due
// to overrun; an event is counted and the caller should re-try
UNDERRUN = 0x80000012, // availableToWrite(), write(), or writeVia() detected a gap in
// output due to underrun (not being called often enough, or with
// enough data); an event is counted and the caller should re-try
};
// Negotiation of format is based on the data provider and data sink, or the data consumer and
// data source, exchanging prioritized arrays of offers and counter-offers until a single offer is
// mutually agreed upon. Each offer is an NBAIO_Format. For simplicity and performance,
// NBAIO_Format is an enum that ties together the most important combinations of the various
// attributes, rather than a struct with separate fields for format, sample rate, channel count,
// interleave, packing, alignment, etc. The reason is that NBAIO_Format tries to abstract out only
// the combinations that are actually needed within AudioFligner. If the list of combinations grows
// too large, then this decision should be re-visited.
enum NBAIO_Format {
Format_Invalid,
Format_SR44_1_C2_I16, // 44.1 kHz PCM stereo interleaved 16-bit signed
Format_SR48_C2_I16, // 48 kHz PCM stereo interleaved 16-bit signed
Format_SR44_1_C1_I16, // 44.1 kHz PCM mono interleaved 16-bit signed
Format_SR48_C1_I16, // 48 kHz PCM mono interleaved 16-bit signed
};
// Return the frame size of an NBAIO_Format in bytes
size_t Format_frameSize(NBAIO_Format format);
// Return the frame size of an NBAIO_Format as a bit shift
size_t Format_frameBitShift(NBAIO_Format format);
// Convert a sample rate in Hz and channel count to an NBAIO_Format
NBAIO_Format Format_from_SR_C(unsigned sampleRate, unsigned channelCount);
// Return the sample rate in Hz of an NBAIO_Format
unsigned Format_sampleRate(NBAIO_Format format);
// Return the channel count of an NBAIO_Format
unsigned Format_channelCount(NBAIO_Format format);
// Callbacks used by NBAIO_Sink::writeVia() and NBAIO_Source::readVia() below.
typedef ssize_t (*writeVia_t)(void *user, void *buffer, size_t count);
typedef ssize_t (*readVia_t)(void *user, const void *buffer, size_t count);
// Abstract class (interface) representing a data port.
class NBAIO_Port : public RefBase {
public:
// negotiate() must called first. The purpose of negotiate() is to check compatibility of
// formats, not to automatically adapt if they are incompatible. It's the responsibility of
// whoever sets up the graph connections to make sure formats are compatible, and this method
// just verifies that. The edges are "dumb" and don't attempt to adapt to bad connections.
// How it works: offerer proposes an array of formats, in descending order of preference from
// offers[0] to offers[numOffers - 1]. If offeree accepts one of these formats, it returns
// the index of that offer. Otherwise, offeree sets numCounterOffers to the number of
// counter-offers (up to a maximumum of the entry value of numCounterOffers), fills in the
// provided array counterOffers[] with its counter-offers, in descending order of preference
// from counterOffers[0] to counterOffers[numCounterOffers - 1], and returns NEGOTIATE.
// Note that since the offerer allocates space for counter-offers, but only the offeree knows
// how many counter-offers it has, there may be insufficient space for all counter-offers.
// In that case, the offeree sets numCounterOffers to the requested number of counter-offers
// (which is greater than the entry value of numCounterOffers), fills in as many of the most
// important counterOffers as will fit, and returns NEGOTIATE. As this implies a re-allocation,
// it should be used as a last resort. It is preferable for the offerer to simply allocate a
// larger space to begin with, and/or for the offeree to tolerate a smaller space than desired.
// Alternatively, the offerer can pass NULL for offers and counterOffers, and zero for
// numOffers. This indicates that it has not allocated space for any counter-offers yet.
// In this case, the offerree should set numCounterOffers appropriately and return NEGOTIATE.
// Then the offerer will allocate the correct amount of memory and retry.
// Format_Invalid is not allowed as either an offer or counter-offer.
// Returns:
// >= 0 Offer accepted.
// NEGOTIATE No offer accepted, and counter-offer(s) optionally made. See above for details.
virtual ssize_t negotiate(const NBAIO_Format offers[], size_t numOffers,
NBAIO_Format counterOffers[], size_t& numCounterOffers);
// Return the current negotiated format, or Format_Invalid if negotiation has not been done,
// or if re-negotiation is required.
virtual NBAIO_Format format() const { return mNegotiated ? mFormat : Format_Invalid; }
protected:
NBAIO_Port(NBAIO_Format format) : mNegotiated(false), mFormat(format),
mBitShift(Format_frameBitShift(format)) { }
virtual ~NBAIO_Port() { }
// Implementations are free to ignore these if they don't need them
bool mNegotiated; // mNegotiated implies (mFormat != Format_Invalid)
NBAIO_Format mFormat; // (mFormat != Format_Invalid) does not imply mNegotiated
size_t mBitShift; // assign in parallel with any assignment to mFormat
};
// Abstract class (interface) representing a non-blocking data sink, for use by a data provider.
class NBAIO_Sink : public NBAIO_Port {
public:
// For the next two APIs:
// 32 bits rolls over after 27 hours at 44.1 kHz; if that concerns you then poll periodically.
// Return the number of frames written successfully since construction.
virtual size_t framesWritten() const { return mFramesWritten; }
// Number of frames lost due to underrun since construction.
virtual size_t framesUnderrun() const { return 0; }
// Number of underruns since construction, where a set of contiguous lost frames is one event.
virtual size_t underruns() const { return 0; }
// Estimate of number of frames that could be written successfully now without blocking.
// When a write() is actually attempted, the implementation is permitted to return a smaller or
// larger transfer count, however it will make a good faith effort to give an accurate estimate.
// Errors:
// NEGOTIATE (Re-)negotiation is needed.
// UNDERRUN write() has not been called frequently enough, or with enough frames to keep up.
// An underrun event is counted, and the caller should re-try this operation.
// WOULD_BLOCK Determining how many frames can be written without blocking would itself block.
virtual ssize_t availableToWrite() const { return SSIZE_MAX; }
// Transfer data to sink from single input buffer. Implies a copy.
// Inputs:
// buffer Non-NULL buffer owned by provider.
// count Maximum number of frames to transfer.
// Return value:
// > 0 Number of frames successfully transferred prior to first error.
// = 0 Count was zero.
// < 0 status_t error occurred prior to the first frame transfer.
// Errors:
// NEGOTIATE (Re-)negotiation is needed.
// WOULD_BLOCK No frames can be transferred without blocking.
// UNDERRUN write() has not been called frequently enough, or with enough frames to keep up.
// An underrun event is counted, and the caller should re-try this operation.
virtual ssize_t write(const void *buffer, size_t count) = 0;
// Transfer data to sink using a series of callbacks. More suitable for zero-fill, synthesis,
// and non-contiguous transfers (e.g. circular buffer or writev).
// Inputs:
// via Callback function that the sink will call as many times as needed to consume data.
// total Estimate of the number of frames the provider has available. This is an estimate,
// and it can provide a different number of frames during the series of callbacks.
// user Arbitrary void * reserved for data provider.
// block Number of frames per block, that is a suggested value for 'count' in each callback.
// Zero means no preference. This parameter is a hint only, and may be ignored.
// Return value:
// > 0 Total number of frames successfully transferred prior to first error.
// = 0 Count was zero.
// < 0 status_t error occurred prior to the first frame transfer.
// Errors:
// NEGOTIATE (Re-)negotiation is needed.
// WOULD_BLOCK No frames can be transferred without blocking.
// UNDERRUN write() has not been called frequently enough, or with enough frames to keep up.
// An underrun event is counted, and the caller should re-try this operation.
//
// The 'via' callback is called by the data sink as follows:
// Inputs:
// user Arbitrary void * reserved for data provider.
// buffer Non-NULL buffer owned by sink that callback should fill in with data,
// up to a maximum of 'count' frames.
// count Maximum number of frames to transfer during this callback.
// Return value:
// > 0 Number of frames successfully transferred during this callback prior to first error.
// = 0 Count was zero.
// < 0 status_t error occurred prior to the first frame transfer during this callback.
virtual ssize_t writeVia(writeVia_t via, size_t total, void *user, size_t block = 0);
protected:
NBAIO_Sink(NBAIO_Format format = Format_Invalid) : NBAIO_Port(format), mFramesWritten(0) { }
virtual ~NBAIO_Sink() { }
// Implementations are free to ignore these if they don't need them
size_t mFramesWritten;
};
// Abstract class (interface) representing a non-blocking data source, for use by a data consumer.
class NBAIO_Source : public NBAIO_Port {
public:
// For the next two APIs:
// 32 bits rolls over after 27 hours at 44.1 kHz; if that concerns you then poll periodically.
// Number of frames read successfully since construction.
virtual size_t framesRead() const { return mFramesRead; }
// Number of frames lost due to overrun since construction.
// Not const because implementations may need to do I/O.
virtual size_t framesOverrun() /*const*/ { return 0; }
// Number of overruns since construction, where a set of contiguous lost frames is one event.
// Not const because implementations may need to do I/O.
virtual size_t overruns() /*const*/ { return 0; }
// Estimate of number of frames that could be read successfully now.
// When a read() is actually attempted, the implementation is permitted to return a smaller or
// larger transfer count, however it will make a good faith effort to give an accurate estimate.
// Errors:
// NEGOTIATE (Re-)negotiation is needed.
// OVERRUN One or more frames were lost due to overrun, try again to read more recent data.
// WOULD_BLOCK Determining how many frames can be read without blocking would itself block.
virtual ssize_t availableToRead() { return SSIZE_MAX; }
// Transfer data from source into single destination buffer. Implies a copy.
// Inputs:
// buffer Non-NULL destination buffer owned by consumer.
// count Maximum number of frames to transfer.
// Return value:
// > 0 Number of frames successfully transferred prior to first error.
// = 0 Count was zero.
// < 0 status_t error occurred prior to the first frame transfer.
// Errors:
// NEGOTIATE (Re-)negotiation is needed.
// WOULD_BLOCK No frames can be transferred without blocking.
// OVERRUN read() has not been called frequently enough, or with enough frames to keep up.
// One or more frames were lost due to overrun, try again to read more recent data.
virtual ssize_t read(void *buffer, size_t count) = 0;
// Transfer data from source using a series of callbacks. More suitable for zero-fill,
// synthesis, and non-contiguous transfers (e.g. circular buffer or readv).
// Inputs:
// via Callback function that the source will call as many times as needed to provide data.
// total Estimate of the number of frames the consumer desires. This is an estimate,
// and it can consume a different number of frames during the series of callbacks.
// user Arbitrary void * reserved for data consumer.
// block Number of frames per block, that is a suggested value for 'count' in each callback.
// Zero means no preference. This parameter is a hint only, and may be ignored.
// Return value:
// > 0 Total number of frames successfully transferred prior to first error.
// = 0 Count was zero.
// < 0 status_t error occurred prior to the first frame transfer.
// Errors:
// NEGOTIATE (Re-)negotiation is needed.
// WOULD_BLOCK No frames can be transferred without blocking.
// OVERRUN read() has not been called frequently enough, or with enough frames to keep up.
// One or more frames were lost due to overrun, try again to read more recent data.
//
// The 'via' callback is called by the data source as follows:
// Inputs:
// user Arbitrary void * reserved for data consumer.
// dest Non-NULL buffer owned by source that callback should consume data from,
// up to a maximum of 'count' frames.
// count Maximum number of frames to transfer during this callback.
// Return value:
// > 0 Number of frames successfully transferred during this callback prior to first error.
// = 0 Count was zero.
// < 0 status_t error occurred prior to the first frame transfer during this callback.
virtual ssize_t readVia(readVia_t via, size_t total, void *user, size_t block = 0);
protected:
NBAIO_Source(NBAIO_Format format = Format_Invalid) : NBAIO_Port(format), mFramesRead(0) { }
virtual ~NBAIO_Source() { }
// Implementations are free to ignore these if they don't need them
size_t mFramesRead;
};
} // namespace android
#endif // ANDROID_AUDIO_NBAIO_H