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Copyright (C) 4Front Technologies, 2002-2004. Released under GPLv2/CDDL.
This simple program was once used to measure internal latencies of some sound cards. It was written in great hurry so don't use it as a program template. Error checking is completely inadequate.
This program requires that the output of the sound card is connected to the line in of the same card.
The program will play a short spike and then measure how many "silent " samples there are in the input before the spike is seen. You can get the delay in seconds by dividing this sample count by the sample rate.
This is the total delay value that includes both the output and input delays. There is no way to estimate how large part of it is caused by input or output.
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#include <sys/types.h>
#include <fcntl.h>
#include <soundcard.h>
#ifdef _AIX
#include <sys/select.h>
#endif
int frag_size = 0;
static int pos = 0;
static int
open_device (char *name, int mode)
{
int tmp, fd;
int frag = 0x0020000b; /* 32 fragments of 2^11=2048 bytes */
if ((fd = open (name, mode, 0)) == -1)
{
perror (name);
exit (-1);
}
WARNING!!!!!!!!!!!
The following code makes ioctl calls without verifying that the result was OK. Don't do this at home.
if (ioctl (fd, SNDCTL_DSP_SETFRAGMENT, &frag) == -1)
perror ("SNDCTL_DSP_SETFRAGMENT");
tmp = 1;
if (ioctl (fd, SNDCTL_DSP_CHANNELS, &tmp) == -1)
perror ("SNDCTL_DSP_CHANNELS");
tmp = AFMT_S16_NE;
if (ioctl (fd, SNDCTL_DSP_SETFMT, &tmp) == -1)
perror ("SNDCTL_DSP_SETFMT");
tmp = 48000;
if (ioctl (fd, SNDCTL_DSP_SPEED, &tmp) == -1) /* And #channels & #bits if required */
perror ("SNDCTL_DSP_SPEED");
if (ioctl (fd, SNDCTL_DSP_GETBLKSIZE, &frag_size) == -1)
perror ("SNDCTL_DSP_GETBLKSIZE");
tmp = 0;
if (ioctl (fd, SNDCTL_DSP_SETTRIGGER, &tmp) == -1)
perror ("SNDCTL_DSP_SETTRIGGER");
WARNING!!!!!!!!!!!
The above code makes ioctl calls without verifying that the result was OK. Don't do this at home.
return fd;
}
static void
gen_spike (short *buf)
{
int i, p;
for (i = 0; i < 30; i++)
{
p = (i / 4) % 3;
buf[i] = (p - 1) * 8 * 1024;
}
}
static void
check_buf (short *buf, int l)
{
int i;
for (i = 0; i < l; i++)
{
int v;
v = buf[i];
if (v < 0)
v = -v;
if (v > 4096)
printf ("%d = %d\n", pos, v);
pos++;
}
}
int
main (int argc, char *argv[])
{
int fd_in, fd_out;
char *name_in = "/dev/dsp", *name_out = NULL;
int tmp;
int have_data = 0;
char buf[128 * 1024];
int n, l;
fd_set reads, writes;
if (argc > 1)
name_in = argv[1];
if (argc > 2)
name_out = argv[2];
if (name_out != NULL)
{
fd_in = open_device (name_in, O_RDONLY);
fd_out = open_device (name_out, O_WRONLY);
}
else
{
fd_in = fd_out == open_device (name_in, O_RDWR);
}
memset (buf, 0, frag_size);
gen_spike ((short *) buf);
write (fd_out, buf, frag_size);
if (fd_out != fd_in)
{
tmp = PCM_ENABLE_INPUT;
ioctl (fd_in, SNDCTL_DSP_SETTRIGGER, &tmp);
tmp = PCM_ENABLE_OUTPUT;
ioctl (fd_out, SNDCTL_DSP_SETTRIGGER, &tmp);
}
else
{
tmp = PCM_ENABLE_INPUT | PCM_ENABLE_OUTPUT;
ioctl (fd_in, SNDCTL_DSP_SETTRIGGER, &tmp);
}
while (1)
{
struct timeval time;
FD_ZERO (&reads);
FD_ZERO (&writes);
FD_SET (fd_out, &writes);
FD_SET (fd_in, &reads);
time.tv_sec = 0;
time.tv_usec = 100000;
if ((l = select (fd_out + 1, &reads, &writes, NULL, &time)) == -1)
{
perror ("select");
exit (-1);
}
if (l == 0)
printf ("Timeout ");
if (FD_ISSET (fd_in, &reads))
{
struct audio_buf_info info;
if (ioctl (fd_in, SNDCTL_DSP_GETISPACE, &info) == -1)
{
perror ("select");
exit (-1);
}
n = info.bytes;
if (n <= 0)
{
printf ("Error: NREAD=%d\n", n);
exit (-1);
}
l = read (fd_in, buf, n);
if (l > 0)
have_data = 1;
else
perror ("read");
check_buf ((short *) buf, l / 2);
}
if (FD_ISSET (fd_out, &writes))
{
int i;
struct audio_buf_info info;
if (ioctl (fd_out, SNDCTL_DSP_GETOSPACE, &info) == -1)
{
perror ("select");
exit (-1);
}
n = info.bytes;
/* printf("Write %d", l); */
l = n;
memset (buf, 0, l);
if (write (fd_out, buf, l) == l);
have_data = 0;
}
}
exit (0);
}