pa_linux_alsa.c

一个开源的sip源代码

    PA_UNLESS( self->pfds = (struct pollfd*)PaUtil_AllocateMemory( (self->capture.nfds +
                    self->playback.nfds) * sizeof (struct pollfd) ), paInsufficientMemory );

    PaUtil_InitializeCpuLoadMeasurer( &self->cpuLoadMeasurer, sampleRate );
    ASSERT_CALL_( PaUnixMutex_Initialize( &self->stateMtx ), paNoError );

error:
    return result;
}

/** Free resources associated with stream, and eventually stream itself.
 *
 * Frees allocated memory, and terminates individual StreamComponents.
 */
static void PaAlsaStream_Terminate( PaAlsaStream *self )
{
    assert( self );

    if( self->capture.pcm )
    {
        PaAlsaStreamComponent_Terminate( &self->capture );
    }
    if( self->playback.pcm )
    {
        PaAlsaStreamComponent_Terminate( &self->playback );
    }

    PaUtil_FreeMemory( self->pfds );
    ASSERT_CALL_( PaUnixMutex_Terminate( &self->stateMtx ), paNoError );

    PaUtil_FreeMemory( self );
}

/** Calculate polling timeout
 *
 * @param frames Time to wait
 * @return Polling timeout in milliseconds
 */
static int CalculatePollTimeout( const PaAlsaStream *stream, unsigned long frames )
{
    assert( stream->streamRepresentation.streamInfo.sampleRate > 0.0 );
    /* Period in msecs, rounded up */
    return (int)ceil( 1000 * frames / stream->streamRepresentation.streamInfo.sampleRate );
}

/** Determine size per host buffer.
 *
 * During this method call, the component's framesPerBuffer attribute gets computed, and the corresponding period size
 * gets configured for the device.
 * @param accurate: If the configured period size is non-integer, this will be set to 0.
 */
static PaError PaAlsaStreamComponent_DetermineFramesPerBuffer( PaAlsaStreamComponent* self, const PaStreamParameters* params,
        unsigned long framesPerUserBuffer, double sampleRate, snd_pcm_hw_params_t* hwParams, int* accurate )
{
    PaError result = paNoError;
    unsigned long bufferSize = params->suggestedLatency * sampleRate, framesPerHostBuffer;
    int dir = 0;
    
    {
        snd_pcm_uframes_t tmp;
        snd_pcm_hw_params_get_buffer_size_min( hwParams, &tmp );
        bufferSize = PA_MAX( bufferSize, tmp );
        snd_pcm_hw_params_get_buffer_size_max( hwParams, &tmp );
        bufferSize = PA_MIN( bufferSize, tmp );
    }

    assert( bufferSize > 0 );

    if( framesPerUserBuffer != paFramesPerBufferUnspecified )
    {
        /* Preferably the host buffer size should be a multiple of the user buffer size */

        if( bufferSize > framesPerUserBuffer )
        {
            snd_pcm_uframes_t remainder = bufferSize % framesPerUserBuffer;
            if( remainder > framesPerUserBuffer / 2. )
                bufferSize += framesPerUserBuffer - remainder;
            else
                bufferSize -= remainder;

            assert( bufferSize % framesPerUserBuffer == 0 );
        }
        else if( framesPerUserBuffer % bufferSize != 0 )
        {
            /*  Find a good compromise between user specified latency and buffer size */
            if( bufferSize > framesPerUserBuffer * .75 )
            {
                bufferSize = framesPerUserBuffer;
            }
            else
            {
                snd_pcm_uframes_t newSz = framesPerUserBuffer;
                while( newSz / 2 >= bufferSize )
                {
                    if( framesPerUserBuffer % (newSz / 2) != 0 )
                    {
                        /* No use dividing any further */
                        break;
                    }
                    newSz /= 2;
                }
                bufferSize = newSz;
            }

            assert( framesPerUserBuffer % bufferSize == 0 );
        }
    }

    /* Using 5 as a base number of periods, we try to approximate the suggested latency (+1 period),
       finding a combination of period/buffer size which best fits these constraints */
    {
        unsigned numPeriods = 4, maxPeriods = 0;
        /* It may be that the device only supports 2 periods for instance */
        dir = 0;
        ENSURE_( snd_pcm_hw_params_get_periods_max( hwParams, &maxPeriods, &dir ), paUnanticipatedHostError );
        assert( maxPeriods > 1 );
        /* One period is not counted as latency */
        maxPeriods -= 1;
        numPeriods = PA_MIN( maxPeriods, numPeriods );

        if( framesPerUserBuffer != paFramesPerBufferUnspecified )
        {
            framesPerHostBuffer = framesPerUserBuffer;
            if( framesPerHostBuffer < bufferSize )
            {
                while( bufferSize / framesPerHostBuffer > numPeriods )
                {
                    framesPerHostBuffer *= 2;
                }
            }
            else
            {
                while( bufferSize / framesPerHostBuffer < numPeriods )
                {
                    if( framesPerUserBuffer % (framesPerHostBuffer / 2) != 0 )
                    {
                        /* Can't be divided any further */
                        break;
                    }
                    framesPerHostBuffer /= 2;
                }
            }

            if( framesPerHostBuffer < framesPerUserBuffer )
            {
                assert( framesPerUserBuffer % framesPerHostBuffer == 0 );
                if( snd_pcm_hw_params_test_period_size( self->pcm, hwParams, framesPerHostBuffer, 0 ) < 0 )
                {
                    if( snd_pcm_hw_params_test_period_size( self->pcm, hwParams, framesPerHostBuffer * 2, 0 ) == 0 )
                        framesPerHostBuffer *= 2;
                    else if( snd_pcm_hw_params_test_period_size( self->pcm, hwParams, framesPerHostBuffer / 2, 0 ) == 0 )
                        framesPerHostBuffer /= 2;
                }
            }
            else
            {
                assert( framesPerHostBuffer % framesPerUserBuffer == 0 );
                if( snd_pcm_hw_params_test_period_size( self->pcm, hwParams, framesPerHostBuffer, 0 ) < 0 )
                {
                    if( snd_pcm_hw_params_test_period_size( self->pcm, hwParams, framesPerHostBuffer + framesPerUserBuffer, 0 ) == 0 )
                        framesPerHostBuffer += framesPerUserBuffer;
                    else if( snd_pcm_hw_params_test_period_size( self->pcm, hwParams, framesPerHostBuffer - framesPerUserBuffer, 0 ) == 0 )
                        framesPerHostBuffer -= framesPerUserBuffer;
                }
            }
        }
        else
        {
            framesPerHostBuffer = bufferSize / numPeriods;
        }
    }

    assert( framesPerHostBuffer > 0 );
    {
        snd_pcm_uframes_t min = 0, max = 0;
        ENSURE_( snd_pcm_hw_params_get_period_size_min( hwParams, &min, NULL ), paUnanticipatedHostError );
        ENSURE_( snd_pcm_hw_params_get_period_size_max( hwParams, &max, NULL ), paUnanticipatedHostError );

        if( framesPerHostBuffer < min )
        {
            PA_DEBUG(( "%s: The determined period size (%lu) is less than minimum (%lu)\n", __FUNCTION__,
                        framesPerHostBuffer, min ));
            framesPerHostBuffer = min;
        }
        else if( framesPerHostBuffer > max )
        {
            PA_DEBUG(( "%s: The determined period size (%lu) is greater than maximum (%lu)\n", __FUNCTION__,
                        framesPerHostBuffer, max ));
            framesPerHostBuffer = max;
        }

        assert( framesPerHostBuffer >= min && framesPerHostBuffer <= max );
        dir = 0;
        ENSURE_( snd_pcm_hw_params_set_period_size_near( self->pcm, hwParams, &framesPerHostBuffer, &dir ),
                paUnanticipatedHostError );
        if( dir != 0 )
        {
            PA_DEBUG(( "%s: The configured period size is non-integer.\n", __FUNCTION__, dir ));
            *accurate = 0;
        }
    }
    self->framesPerBuffer = framesPerHostBuffer;

error:
    return result;
}

/* We need to determine how many frames per host buffer (period) to use.  Our
 * goals are to provide the best possible performance, but also to
 * honor the requested latency settings as closely as we can. Therefore this
 * decision is based on:
 *
 *   - the period sizes that playback and/or capture support.  The
 *     host buffer size has to be one of these.
 *   - the number of periods that playback and/or capture support.
 *
 * We want to make period_size*(num_periods-1) to be as close as possible
 * to latency*rate for both playback and capture.
 *
 * This method will determine suitable period sizes for capture and playback handles, and report the maximum number of
 * frames per host buffer. The latter is relevant, in case we should be so unfortunate that the period size differs
 * between capture and playback. If this should happen, the stream's hostBufferSizeMode attribute will be set to
 * paUtilBoundedHostBufferSize, because the best we can do is limit the size of individual host buffers to the upper
 * bound. The size of host buffers scheduled for processing should only matter if the user has specified a buffer size,
 * but when he/she does we must strive for an optimal configuration. By default we'll opt for a fixed host buffer size,
 * which should be fine if the period size is the same for capture and playback. In general, if there is a specified user
 * buffer size, this method tries it best to determine a period size which is a multiple of the user buffer size.
 *
 * The framesPerBuffer attributes of the individual capture and playback components of the stream are set to corresponding
 * values determined here. Since these should be reported as 
 *
 * This is one of those blocks of code that will just take a lot of
 * refinement to be any good.
 *
 * In the full-duplex case it is possible that the routine was unable
 * to find a number of frames per buffer acceptable to both devices
 * TODO: Implement an algorithm to find the value closest to acceptance
 * by both devices, to minimize difference between period sizes?
 *
 * @param determinedFramesPerHostBuffer: The determined host buffer size.
 */
static PaError PaAlsaStream_DetermineFramesPerBuffer( PaAlsaStream* self, double sampleRate, const PaStreamParameters* inputParameters,
        const PaStreamParameters* outputParameters, unsigned long framesPerUserBuffer, snd_pcm_hw_params_t* hwParamsCapture,
        snd_pcm_hw_params_t* hwParamsPlayback, PaUtilHostBufferSizeMode* hostBufferSizeMode )
{
    PaError result = paNoError;
    unsigned long framesPerHostBuffer = 0;
    int dir = 0;
    int accurate = 1;

    if( self->capture.pcm && self->playback.pcm )
    {
        if( framesPerUserBuffer == paFramesPerBufferUnspecified )
        {
            snd_pcm_uframes_t desiredLatency, e, minPeriodSize, maxPeriodSize, optimalPeriodSize, periodSize,
                              minCapture, minPlayback, maxCapture, maxPlayback;

            /* Come up with a common desired latency */

            dir = 0;
            ENSURE_( snd_pcm_hw_params_get_period_size_min( hwParamsCapture, &minCapture, &dir ), paUnanticipatedHostError );
            dir = 0;
            ENSURE_( snd_pcm_hw_params_get_period_size_min( hwParamsPlayback, &minPlayback, &dir ), paUnanticipatedHostError );
            dir = 0;
            ENSURE_( snd_pcm_hw_params_get_period_size_max( hwParamsCapture, &maxCapture, &dir ), paUnanticipatedHostError );
            dir = 0;
            ENSURE_( snd_pcm_hw_params_get_period_size_max( hwParamsPlayback, &maxPlayback, &dir ), paUnanticipatedHostError );
            minPeriodSize = PA_MAX( minPlayback, minCapture );
            maxPeriodSize = PA_MIN( maxPlayback, maxCapture );
            PA_UNLESS( minPeriodSize <= maxPeriodSize, paBadIODeviceCombination );

            desiredLatency = (snd_pcm_uframes_t)(PA_MIN( outputParameters->suggestedLatency, inputParameters->suggestedLatency )
                    * sampleRate);
            /* Clamp desiredLatency */
            {
                snd_pcm_uframes_t maxBufferSize;
                snd_pcm_uframes_t maxBufferSizeCapture, maxBufferSizePlayback;
                ENSURE_( snd_pcm_hw_params_get_buffer_size_max( hwParamsCapture, &maxBufferSizeCapture ), paUnanticipatedHostError );
                ENSURE_( snd_pcm_hw_params_get_buffer_size_max( hwParamsPlayback, &maxBufferSizePlayback ), paUnanticipatedHostError );
                maxBufferSize = PA_MIN( maxBufferSizeCapture, maxBufferSizePlayback );

                desiredLatency = PA_MIN( desiredLatency, maxBufferSize );
            }

            /* Find the closest power of 2 */
            e = ilogb( minPeriodSize );
            if( minPeriodSize & (minPeriodSize - 1) )
                e += 1;
            periodSize = (snd_pcm_uframes_t)pow( 2, e );

            while( periodSize <= maxPeriodSize )
            {
                if( snd_pcm_hw_params_test_period_size( self->playback.pcm, hwParamsPlayback, periodSize, 0 ) >= 0 &&
                        snd_pcm_hw_params_test_period_size( self->capture.pcm, hwParamsCapture, periodSize, 0 ) >= 0 )
                    break;  /* Ok! */

                periodSize *= 2;
            }

            /* 4 periods considered optimal */
            optimalPeriodSize = PA_MAX( desiredLatency / 4, minPeriodSize );
            optimalPeriodSize = PA_MIN( optimalPeriodSize, maxPeriodSize );

            /* Find the closest power of 2 */
            e = ilogb( optimalPeriodSize );
            if( optimalPeriodSize & (optimalPeriodSize - 1) )
                e += 1;
            optimalPeriodSize = (snd_pcm_uframes_t)pow( 2, e );

            while( optimalPeriodSize >= periodSize )
            {
                if( snd_pcm_hw_params_test_period_size( self->capture.pcm, hwParamsCapture, optimalPeriodSize, 0 ) < 0 )
                    continue;
                if( snd_pcm_hw_params_test_period_size( self->playback.pcm, hwParamsPlayback, optimalPeriodSize, 0 ) >= 0 )
                    break;
                optimalPeriodSize /= 2;
            }
            if( optimalPeriodSize > periodSize )
                periodSize = optimalPeriodSize;

            if( periodSize <= maxPeriodSize )
            {
                /* Looks good, the periodSize _should_ be acceptable by both devices */
                ENSURE_( snd_pcm_hw_params_set_period_size( self->capture.pcm, hwParamsCapture, periodSize, 0 ),
                        paUnanticipatedHostError );
                ENSURE_( snd_pcm_hw_params_set_period_size( self->playback.pcm, hwParamsPlayback, periodSize, 0 ),
                        paUnanticipatedHostError );
                self->capture.framesPerBuffer = self->playback.framesPerBuffer = periodSize;
                framesPerHostBuffer = periodSize;
            }
            else
            {
                /* Unable to find a common period size, oh well */
                optimalPeriodSize = PA_MAX( desiredLatency / 4, minPeriodSize );
                optimalPeriodSize = PA_MIN( optimalPeriodSize, maxPeriodSize );

                self->capture.framesPerBuffer = optimalPeriodSize;
                dir = 0;
                ENSURE_( snd_pcm_hw_params_set_period_size_near( self->capture.pcm, hwParamsCapture, &self->capture.framesPerBuffer, &dir ),
                        paUnanticipatedHostError );
                self->playback.framesPerBuffer = optimalPeriodSize;
                dir = 0;
                ENSURE_( snd_pcm_hw_params_set_period_size_