PortAudio ASIO driver issue

[sw2719]

When I try to use ASIO with Moondrop Dawn Pro, there's no audio and following stack trace is spammed on terminal.

java.lang.RuntimeException: Wait timed out
        at com.portaudio.BlockingStream.writeFloats(Native Method)
        at com.portaudio.BlockingStream.write(BlockingStream.java:119)
        at bms.player.beatoraja.audio.PortAudioDriver.run(Unknown Source)
        at java.base/java.lang.Thread.run(Thread.java:1570)

Weirdly enough, it works fine on rhythm games which use FMOD. I also tested it in foobar2000 with ASIO plugin. Setting beatoraja output to REAPER ReaRoute and outputting to DAC also works. I assume it's some kind of compatibility issue between PortAudio and the ASIO driver.

Any help would be greatly appreciated.

[Merrg1n]

I can reproduce this issue on the Luxury&Precision W2 DAC. After examining the ASIO driver logs, I found that PortAudio is attempting to create an audio stream with a BufferSize of 1, which prevents ASIO from properly outputting audio.

[Merrg1n]

TL;DR：Changing the Audio Buffer Size(KB) to $16*n+1$ (I chose 321).

After debugging Portaudio and ASIO drivers, I discovered that the ASIO driver returns unusual Buffer ranges. On my device driver, it returned bufferMinSize = 1 and bufferMaxSize = 500, while requiring bufferGranularity = 16. This causes Portaudio to calculate framesPerHostBuffer incorrectly. The specific code is as follows:

https://github.com/PortAudio/portaudio/blob/27c85c52d70d692c1e7ee017b339891e53a9fffd/src/hostapi/asio/pa_asio.cpp#L2265

    /* Using blocking i/o interface... */
    if( usingBlockingIo )
    {
/** @todo REVIEW selection of host buffer size for blocking i/o */

        framesPerHostBuffer = SelectHostBufferSize( 0, framesPerBuffer, driverInfo );

    }
    else /* Using callback interface... */
    {
        /* ... */
    }


    PA_DEBUG(("PaAsioOpenStream: framesPerHostBuffer :%d
",  framesPerHostBuffer));

    asioError = ASIOCreateBuffers( stream->asioBufferInfos,
            inputChannelCount+outputChannelCount,
            framesPerHostBuffer, &asioCallbacks_ );

In Beatoraja, usingBlockingIo = true, and framesPerBuffer is the deviceBufferSize from config (the name "deviceBufferSize" is somewhat confusing).

The general logic in the SelectHostBufferSize function is as follows:

https://github.com/PortAudio/portaudio/blob/27c85c52d70d692c1e7ee017b339891e53a9fffd/src/hostapi/asio/pa_asio.cpp#L1820

static unsigned long SelectHostBufferSize(
        unsigned long targetBufferingLatencyFrames,
        unsigned long userFramesPerBuffer, PaAsioDriverInfo *driverInfo )
{
    unsigned long result = 0;

    if( userFramesPerBuffer != 0 )
    {
        result = SelectHostBufferSizeForSpecifiedUserFramesPerBuffer(
                targetBufferingLatencyFrames, userFramesPerBuffer, driverInfo );
    }

    if( result == 0 )
    {
        result = SelectHostBufferSizeForUnspecifiedUserFramesPerBuffer(
                targetBufferingLatencyFrames, driverInfo );
    }

    return result;
}

Debugging revealed that SelectHostBufferSizeForSpecifiedUserFramesPerBuffer returns 0, which leads to SelectHostBufferSizeForUnspecifiedUserFramesPerBuffer being called. This function ultimately returns bufferMinSize, resulting in the creation of an ASIO stream with bufferSize of 1, which doesn't work properly on some devices.

Looking specifically at the logic of SelectHostBufferSizeForSpecifiedUserFramesPerBuffer, it calculates as follows:

https://github.com/PortAudio/portaudio/blob/27c85c52d70d692c1e7ee017b339891e53a9fffd/src/hostapi/asio/pa_asio.cpp#L1792

    else /* modulo granularity */
    {
        /* We assume bufferMinSize is a multiple of bufferGranularity. */

        /* Search all multiples of bufferGranularity in the range
           [bufferMinSize,bufferMaxSize] for multiples of userFramesPerBuffer.
           We prefer the first multiple that is equal or greater than
           targetBufferingLatencyFrames, or failing that, the largest multiple
           less than targetBufferingLatencyFrames.
        */
        unsigned long x = (unsigned long)driverInfo->bufferMinSize;
        do {
            if( (x % userFramesPerBuffer) == 0 )
            {
                /* any multiple of userFramesPerBuffer is acceptable */
                result = x;
                if( result >= targetBufferingLatencyFrames )
                    break; /* stop. a value >= to targetBufferingLatencyFrames is ideal. */
            }

            x += driverInfo->bufferGranularity;
        } while( x <= (unsigned long)driverInfo->bufferMaxSize );
    }

Since bufferMinSize = 1 and bufferGranularity = 16, Portaudio tries all buffer sizes of the form $16n+1$. It's actually difficult for this value to be divisible by a specific userFramesPerBuffer, as this variable is typically a power of 2 (Beatoraja's default is 384). On my device, it doesn't actually require the buffer size to be a multiple of 16, so I set it to 321, and it worked normally.