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/*
* Purpose: A program that demonstrates use of syncronization groups.
* Copyright (C) 4Front Technologies, 2002-2004. Released under GPLv2/CDDL.
*
* Description:
* This program opens three audio devices (hard coded in the program)
* and creates a syncronization group using {!nlink SNDCTL_DSP_SYNCGROUP}.
*
* Next it starts all the devices joined in the group simultaneously
* by calling {!nlink SNDCTL_DSP_SYNCSTART}. Finally it will keep copying
* audio input from the 3rd device to the other two ones.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <soundcard.h>
#define MAX_DEV 10
int
main (int argc, char *argv[])
{
int i, id, fd[MAX_DEV], ndevs = 0;
char buf[32768] = { 0 };
oss_syncgroup group;
group.id = 0;
group.mode = PCM_ENABLE_OUTPUT;
/*
* Open the devices listed on command line
*/
if (argc < 2)
exit (-1);
for (i = 1; i < argc; i++)
{
if ((fd[ndevs] = open (argv[i], O_WRONLY, 0)) == -1)
{
perror (argv[i]);
exit (-1);
}
if (ioctl (fd[ndevs], SNDCTL_DSP_SYNCGROUP, &group) == -1)
{
perror ("SNDCTL_DSP_SYNCGROUP");
exit (-1);
}
/*
* Note! It is very important to write some data to all output devices
* between calling SNDCTL_DSP_SYNCGROUP and SNDCTL_DSP_SYNCSTART. Otherwise
* playback will not start properly. However do not write more data than
* there is room in device's DMA buffer. Recommended amount of prteload data
* is one full fragment.
*
* In applications that record audio, process it and then play back it's
* necessary to write two fragments of silence to the output device(s) before
* starting the group. Otherwise output device(s) will run out of data before
* the first read from the input device returns.
*/
if (write (fd[ndevs], buf, sizeof (buf)) != sizeof (buf))
{
perror ("write");
exit (-1);
}
ndevs++;
}
printf ("Sync group %x created with %d devices\n", group.id, ndevs);
id = group.id;
if (ioctl (fd[0], SNDCTL_DSP_SYNCSTART, &id) == -1)
{
perror ("SNDCTL_DSP_SYNCSTART");
exit (-1);
}
while (1)
{
for (i = 0; i < ndevs; i++)
if (write (fd[i], buf, sizeof (buf)) != sizeof (buf))
{
perror ("write2");
exit (-1);
}
}
exit (0);
}
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