pa_asio.cpp

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                deviceInfo->maxInputChannels  = paAsioDriverInfo.inputChannelCount;
                deviceInfo->maxOutputChannels = paAsioDriverInfo.outputChannelCount;

                deviceInfo->defaultSampleRate = 0.;
                bool foundDefaultSampleRate = false;
                for( int j=0; j < PA_DEFAULTSAMPLERATESEARCHORDER_COUNT_; ++j )
                {
                    ASIOError asioError = ASIOCanSampleRate( defaultSampleRateSearchOrder_[j] );
                    if( asioError != ASE_NoClock && asioError != ASE_NotPresent )
                    {
                        deviceInfo->defaultSampleRate = defaultSampleRateSearchOrder_[j];
                        foundDefaultSampleRate = true;
                        break;
                    }
                }

                PA_DEBUG(("PaAsio_Initialize: drv:%d defaultSampleRate = %f\n", i, deviceInfo->defaultSampleRate));

                if( foundDefaultSampleRate ){

                    /* calculate default latency values from bufferPreferredSize
                        for default low latency, and bufferPreferredSize * 3
                        for default high latency.
                        use the default sample rate to convert from samples to
                        seconds. Without knowing what sample rate the user will
                        use this is the best we can do.
                    */

                    double defaultLowLatency =
                            paAsioDriverInfo.bufferPreferredSize / deviceInfo->defaultSampleRate;

                    deviceInfo->defaultLowInputLatency = defaultLowLatency;
                    deviceInfo->defaultLowOutputLatency = defaultLowLatency;

                    long defaultHighLatencyBufferSize =
                            paAsioDriverInfo.bufferPreferredSize * 3;

                    if( defaultHighLatencyBufferSize > paAsioDriverInfo.bufferMaxSize )
                        defaultHighLatencyBufferSize = paAsioDriverInfo.bufferMaxSize;

                    double defaultHighLatency =
                            defaultHighLatencyBufferSize / deviceInfo->defaultSampleRate;

                    if( defaultHighLatency < defaultLowLatency )
                        defaultHighLatency = defaultLowLatency; /* just incase the driver returns something strange */ 
                            
                    deviceInfo->defaultHighInputLatency = defaultHighLatency;
                    deviceInfo->defaultHighOutputLatency = defaultHighLatency;
                    
                }else{

                    deviceInfo->defaultLowInputLatency = 0.;
                    deviceInfo->defaultLowOutputLatency = 0.;
                    deviceInfo->defaultHighInputLatency = 0.;
                    deviceInfo->defaultHighOutputLatency = 0.;
                }

                PA_DEBUG(("PaAsio_Initialize: drv:%d defaultLowInputLatency = %f\n", i, deviceInfo->defaultLowInputLatency));
                PA_DEBUG(("PaAsio_Initialize: drv:%d defaultLowOutputLatency = %f\n", i, deviceInfo->defaultLowOutputLatency));
                PA_DEBUG(("PaAsio_Initialize: drv:%d defaultHighInputLatency = %f\n", i, deviceInfo->defaultHighInputLatency));
                PA_DEBUG(("PaAsio_Initialize: drv:%d defaultHighOutputLatency = %f\n", i, deviceInfo->defaultHighOutputLatency));

                asioDeviceInfo->minBufferSize = paAsioDriverInfo.bufferMinSize;
                asioDeviceInfo->maxBufferSize = paAsioDriverInfo.bufferMaxSize;
                asioDeviceInfo->preferredBufferSize = paAsioDriverInfo.bufferPreferredSize;
                asioDeviceInfo->bufferGranularity = paAsioDriverInfo.bufferGranularity;


                asioDeviceInfo->asioChannelInfos = (ASIOChannelInfo*)PaUtil_GroupAllocateMemory(
                        asioHostApi->allocations,
                        sizeof(ASIOChannelInfo) * (deviceInfo->maxInputChannels
                                + deviceInfo->maxOutputChannels) );
                if( !asioDeviceInfo->asioChannelInfos )
                {
                    result = paInsufficientMemory;
                    goto error;
                }

                int a;

                for( a=0; a < deviceInfo->maxInputChannels; ++a ){
                    asioDeviceInfo->asioChannelInfos[a].channel = a;
                    asioDeviceInfo->asioChannelInfos[a].isInput = ASIOTrue;
                    ASIOError asioError = ASIOGetChannelInfo( &asioDeviceInfo->asioChannelInfos[a] );
                    if( asioError != ASE_OK )
                    {
                        result = paUnanticipatedHostError;
                        PA_ASIO_SET_LAST_ASIO_ERROR( asioError );
                        goto error;
                    }
                }

                for( a=0; a < deviceInfo->maxOutputChannels; ++a ){
                    int b = deviceInfo->maxInputChannels + a;
                    asioDeviceInfo->asioChannelInfos[b].channel = a;
                    asioDeviceInfo->asioChannelInfos[b].isInput = ASIOFalse;
                    ASIOError asioError = ASIOGetChannelInfo( &asioDeviceInfo->asioChannelInfos[b] );
                    if( asioError != ASE_OK )
                    {
                        result = paUnanticipatedHostError;
                        PA_ASIO_SET_LAST_ASIO_ERROR( asioError );
                        goto error;
                    }
                }


                /* unload the driver */
                ASIOExit();

                (*hostApi)->deviceInfos[ (*hostApi)->info.deviceCount ] = deviceInfo;
                ++(*hostApi)->info.deviceCount;
            }
        }
    }

    if( (*hostApi)->info.deviceCount > 0 )
    {
        (*hostApi)->info.defaultInputDevice = 0;
        (*hostApi)->info.defaultOutputDevice = 0;
    }
    else
    {
        (*hostApi)->info.defaultInputDevice = paNoDevice;
        (*hostApi)->info.defaultOutputDevice = paNoDevice;
    }


    (*hostApi)->Terminate = Terminate;
    (*hostApi)->OpenStream = OpenStream;
    (*hostApi)->IsFormatSupported = IsFormatSupported;

    PaUtil_InitializeStreamInterface( &asioHostApi->callbackStreamInterface, CloseStream, StartStream,
                                      StopStream, AbortStream, IsStreamStopped, IsStreamActive,
                                      GetStreamTime, GetStreamCpuLoad,
                                      PaUtil_DummyRead, PaUtil_DummyWrite,
                                      PaUtil_DummyGetReadAvailable, PaUtil_DummyGetWriteAvailable );

    PaUtil_InitializeStreamInterface( &asioHostApi->blockingStreamInterface, CloseStream, StartStream,
                                      StopStream, AbortStream, IsStreamStopped, IsStreamActive,
                                      GetStreamTime, PaUtil_DummyGetCpuLoad,
                                      ReadStream, WriteStream, GetStreamReadAvailable, GetStreamWriteAvailable );

    return result;

error:
    if( asioHostApi )
    {
        if( asioHostApi->allocations )
        {
            PaUtil_FreeAllAllocations( asioHostApi->allocations );
            PaUtil_DestroyAllocationGroup( asioHostApi->allocations );
        }

        PaUtil_FreeMemory( asioHostApi );
    }
    return result;
}


static void Terminate( struct PaUtilHostApiRepresentation *hostApi )
{
    PaAsioHostApiRepresentation *asioHostApi = (PaAsioHostApiRepresentation*)hostApi;

    /*
        IMPLEMENT ME:
            - clean up any resources not handled by the allocation group
    */

    if( asioHostApi->allocations )
    {
        PaUtil_FreeAllAllocations( asioHostApi->allocations );
        PaUtil_DestroyAllocationGroup( asioHostApi->allocations );
    }

    PaUtil_FreeMemory( asioHostApi );
}


static PaError IsFormatSupported( struct PaUtilHostApiRepresentation *hostApi,
                                  const PaStreamParameters *inputParameters,
                                  const PaStreamParameters *outputParameters,
                                  double sampleRate )
{
    PaError result = paNoError;
    PaAsioHostApiRepresentation *asioHostApi = (PaAsioHostApiRepresentation*)hostApi;
    PaAsioDriverInfo *driverInfo = &asioHostApi->openAsioDriverInfo;
    int inputChannelCount, outputChannelCount;
    PaSampleFormat inputSampleFormat, outputSampleFormat;
    PaDeviceIndex asioDeviceIndex;                                  
    ASIOError asioError;
    
    if( inputParameters && outputParameters )
    {
        /* full duplex ASIO stream must use the same device for input and output */

        if( inputParameters->device != outputParameters->device )
            return paBadIODeviceCombination;
    }
    
    if( inputParameters )
    {
        inputChannelCount = inputParameters->channelCount;
        inputSampleFormat = inputParameters->sampleFormat;

        /* all standard sample formats are supported by the buffer adapter,
            this implementation doesn't support any custom sample formats */
        if( inputSampleFormat & paCustomFormat )
            return paSampleFormatNotSupported;
            
        /* unless alternate device specification is supported, reject the use of
            paUseHostApiSpecificDeviceSpecification */

        if( inputParameters->device == paUseHostApiSpecificDeviceSpecification )
            return paInvalidDevice;

        asioDeviceIndex = inputParameters->device;

        /* validate inputStreamInfo */
        /** @todo do more validation here */
        // if( inputParameters->hostApiSpecificStreamInfo )
        //    return paIncompatibleHostApiSpecificStreamInfo; /* this implementation doesn't use custom stream info */
    }
    else
    {
        inputChannelCount = 0;
    }

    if( outputParameters )
    {
        outputChannelCount = outputParameters->channelCount;
        outputSampleFormat = outputParameters->sampleFormat;

        /* all standard sample formats are supported by the buffer adapter,
            this implementation doesn't support any custom sample formats */
        if( outputSampleFormat & paCustomFormat )
            return paSampleFormatNotSupported;
            
        /* unless alternate device specification is supported, reject the use of
            paUseHostApiSpecificDeviceSpecification */

        if( outputParameters->device == paUseHostApiSpecificDeviceSpecification )
            return paInvalidDevice;

        asioDeviceIndex = outputParameters->device;

        /* validate outputStreamInfo */
        /** @todo do more validation here */
        // if( outputParameters->hostApiSpecificStreamInfo )
        //    return paIncompatibleHostApiSpecificStreamInfo; /* this implementation doesn't use custom stream info */
    }
    else
    {
        outputChannelCount = 0;
    }



    /* if an ASIO device is open we can only get format information for the currently open device */

    if( asioHostApi->openAsioDeviceIndex != paNoDevice 
			&& asioHostApi->openAsioDeviceIndex != asioDeviceIndex )
    {
        return paDeviceUnavailable;
    }


    /* NOTE: we load the driver and use its current settings
        rather than the ones in our device info structure which may be stale */

    /* open the device if it's not already open */
    if( asioHostApi->openAsioDeviceIndex == paNoDevice )
    {
        result = LoadAsioDriver( asioHostApi->inheritedHostApiRep.deviceInfos[ asioDeviceIndex ]->name,
                driverInfo, asioHostApi->systemSpecific );
        if( result != paNoError )
            return result;
    }

    /* check that input device can support inputChannelCount */
    if( inputChannelCount > 0 )
    {
        if( inputChannelCount > driverInfo->inputChannelCount )
        {
            result = paInvalidChannelCount;
            goto done;
        }
    }

    /* check that output device can support outputChannelCount */
    if( outputChannelCount )
    {
        if( outputChannelCount > driverInfo->outputChannelCount )
        {
            result = paInvalidChannelCount;
            goto done;
        }
    }
    
    /* query for sample rate support */
    asioError = ASIOCanSampleRate( sampleRate );
    if( asioError == ASE_NoClock || asioError == ASE_NotPresent )
    {
        result = paInvalidSampleRate;
        goto done;
    }

done:
    /* close the device if it wasn't already open */
    if( asioHostApi->openAsioDeviceIndex == paNoDevice )
    {
        ASIOExit(); /* not sure if we should check for errors here */
    }

    if( result == paNoError )
        return paFormatIsSupported;
    else
        return result;
}



/* PaAsioStream - a stream data structure specifically for this implementation */

typedef struct PaAsioStream
{
    PaUtilStreamRepresentation streamRepresentation;
    PaUtilCpuLoadMeasurer cpuLoadMeasurer;
    PaUtilBufferProcessor bufferProcessor;

    PaAsioHostApiRepresentation *asioHostApi;
    unsigned long framesPerHostCallback;

    /* ASIO driver info  - these may not be needed for the life of the stream,
        but store them here until we work out how format conversion is going
        to work. */

    ASIOBufferInfo *asioBufferInfos;
    ASIOChannelInfo *asioChannelInfos;
    long inputLatency, outputLatency; // actual latencies returned by asio

    long inputChannelCount, outputChannelCount;
    bool postOutput;

    void **bufferPtrs; /* this is carved up for inputBufferPtrs and outputBufferPtrs */
    void **inputBufferPtrs[2];
    void **outputBufferPtrs[2];

    PaAsioBufferConverter *inputBufferConverter;
    long inputShift;
    PaAsioBufferConverter *outputBufferConverter;
    long outputShift;

    volatile bool stopProcessing;
    int stopPlayoutCount;
    HANDLE completedBuffersPlayedEvent;

    bool streamFinishedCallbackCalled;
    volatile int isActive;
    volatile bool zeroOutput; /* all future calls to the callback will output silence */

    volatile long reenterCount;
    volatile long reenterError;

    PaStreamCallbackFlags callbackFlags;
}
PaAsioStream;

static PaAsioStream *theAsioStream = 0; /* due to ASIO sdk limitations there can be only one stream */


static void ZeroOutputBuffers( PaAsioStream *stream, long index )
{
    int i;

    for( i=0; i < stream->outputChannelCount; ++i )
    {