linux_audiodrv.cpp

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//
// 1997/09/27 21:38:01
//
// --------------------------------------------------------------------------
// ``Open Sound System (OSS)'' / Linux specific audio interface.
// --------------------------------------------------------------------------

#include "audiodrv.h"

audioDriver::audioDriver()
{
        // Reset everything.
        errorString = "None";
        frequency = 0;
        channels = 0;
        encoding = 0;
        precision = 0;
        audioHd = (-1);
}

bool audioDriver::IsThere()
{
        // Check device availability and write permissions.
        return (access(AUDIODEVICE,W_OK)==0);
}

bool audioDriver::Open(udword inFreq, int inPrecision, int inChannels,
                                           int inFragments, int inFragBase)
{
        if ((audioHd=open(AUDIODEVICE,O_WRONLY,0)) == (-1))
    {
                errorString = "AUDIO: Could not open audio device.";
                return false;
    }
        
        // Transfer input parameters to this object.
        // May later be replaced with driver defaults.
        frequency = inFreq;
        precision = inPrecision;
        channels = inChannels;
        fragments = inFragments;
        fragSizeBase = inFragBase;

        // Set sample precision and type of encoding.
        int dsp_sampleSize;
        if (precision == SIDEMU_16BIT)
                dsp_sampleSize = 16;
        else  // if (precision == SIDEMU_8BIT)
                dsp_sampleSize = 8;
        if (ioctl(audioHd,SNDCTL_DSP_SAMPLESIZE,&dsp_sampleSize) == (-1))
    {
                errorString = "AUDIO: Could not set sample size.";
                return false;
    }
        // Verify and accept the sample precision the driver accepted.
        if (dsp_sampleSize == 16)
    {
                precision = SIDEMU_16BIT;
                encoding = SIDEMU_SIGNED_PCM;
    }
        else if (dsp_sampleSize == 8)
    {
                precision = SIDEMU_8BIT;
                encoding = SIDEMU_UNSIGNED_PCM;
    }
        else
        {
                errorString = "AUDIO: Could not set sample size.";
                return false;
        }

        // Set mono/stereo.
        int dsp_stereo;
        if (channels == SIDEMU_STEREO)
                dsp_stereo = 1;
        else  // if (channels == SIDEMU_MONO)
                dsp_stereo = 0;
        if (ioctl(audioHd,SNDCTL_DSP_STEREO,&dsp_stereo) == (-1))
    {
                errorString = "AUDIO: Could not set mono/stereo.";
                return false;
    }
        // Verify and accept the number of channels the driver accepted.
        if (dsp_stereo == 1)
                channels = SIDEMU_STEREO;
        else if (dsp_stereo == 0)
                channels = SIDEMU_MONO;
        else
    {
                errorString = "AUDIO: Could not set mono/stereo.";
                return false;
    }
        
        // Set frequency.
        int dsp_speed = frequency;
        if (ioctl(audioHd,SNDCTL_DSP_SPEED,&dsp_speed) == (-1))
    {
                errorString = "AUDIO: Could not set frequency.";
                return false;
    }
        // Accept the frequency the driver accepted.
        frequency = dsp_speed;
        
        // N fragments of size (2 ^ S) bytes
        //               NNNNSSSS
        // e.g. frag = 0x0004000e;
        // fragments should be out of [2,3,..,255]
        // fragSizeBase should be out of [7,8,...,17]
        // depending on the kernel audio driver buffer size
        int frag = (fragments << 16) | fragSizeBase;
        ioctl(audioHd,SNDCTL_DSP_SETFRAGMENT,&frag);
        ioctl(audioHd,SNDCTL_DSP_GETBLKSIZE,&blockSize);
        
        audio_buf_info myAudInfo;
        if (ioctl(audioHd,SNDCTL_DSP_GETOSPACE,&myAudInfo) == (-1))
        {
                errorString = "AUDIO: Could not get audio_buf_info.";
                return false;
        }
        fragments = myAudInfo.fragstotal;
        //cout << "fragsize = " << (int)myAudInfo.fragsize << endl;
        //cout << "bytes = " << (int)myAudInfo.bytes << endl;
        
    return true;
}

// Close an opened audio device, free any allocated buffers and
// reset any variables that reflect the current state.
void audioDriver::Close()
{
        if (audioHd != (-1))
    {
                close(audioHd);
                audioHd = (-1);
    }
}

void audioDriver::Play(ubyte* pBuffer, int bufferSize)
{
        if (audioHd != (-1))
        {
                write(audioHd,pBuffer,bufferSize);
        }
}

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