| | Open Sound System |
| Do you have problems with sound/audio application development? Don't panic! Click here for help! |
Copyright (C) 4Front Technologies, 2002-2004. Released under GPLv2/CDDL.
This program reads stdin and plays the input to an audio device using morse code. The stdin input is supposed to be originated from a file. This program is not capable to play live keyboard input.
This is a great OSS programming example because it shows how simple audio programming can be with OSS.
You can use this program as a template. Just replace the while loop of the main routine by your own code.
The morse2.c and morse3.c programs are more complex versions of the same program. They demonstrate how the select system call can be used for serving the audio device in parallel while handling terminal input.
This program was tuned to be used when practising for the finnish morse code test for radio amateurs. It supports the scandinavian version of the morse code alphabet used in this test.
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <fcntl.h> #include <sys/soundcard.h> #include <math.h> #include <signal.h> #include <sys/time.h> #include <sys/types.h> #define BUFSZ (16*1024) #define SRATE 48000 #define ATTACK 100 #define CHARDELAY 3 int charspeed = 25; int dotsize, charsize; int audiofd = -1; char randomlist[256]; int nrandom; static int ncodes; double a, step;
The genpulse() routine converts generates a single dot, dash or a pause between the symbols. this is done by generating sine wave (using cos()). It's pretty slow but works for us.
#include "charlist.h"
static int
genpulse (short *buf, int w, int state)
{
int i, l;
a = 0.0;
l = w * dotsize;
for (i = 0; i < ATTACK; i++)
{
double tmp = 0x7fff * cos (a * M_PI / 180.0);
tmp *= (double) (i) / (double) ATTACK;
*buf++ = (int) tmp *state;
a += step;
if (a > 360.0)
a -= 360.0;
}
for (i = ATTACK; i < l - ATTACK; i++)
{
double tmp = 0x7fff * cos (a * M_PI / 180.0);
*buf++ = (int) tmp *state;
a += step;
if (a > 360.0)
a -= 360.0;
}
for (i = l - ATTACK; i < l; i++)
{
double tmp = 0x7fff * cos (a * M_PI / 180.0);
tmp *= (double) (l - i) / (double) ATTACK;
*buf++ = (int) tmp *state;
a += step;
if (a > 360.0)
a -= 360.0;
}
return l;
}
The genmorse() routine converts an ASCII character to the equivivalent audio morse code signal.
static int
genmorse (short *buf, char c)
{
int l = 0, i;
const char *s;
//printf("%c", c);
//fflush(stdout);
if (c == ' ')
return genpulse (buf, 4, 0);
for (i = 0; i < ncodes; i++)
if (Chars[i] == c)
{
s = Codes[i];
while (*s)
{
if (*s++ == '.')
l += genpulse (&buf[l], 1, 1);
else
l += genpulse (&buf[l], 3, 1);
l += genpulse (&buf[l], 1, 0);
}
l += genpulse (&buf[l], CHARDELAY, 0);
return l;
}
return 0;
}
The playchar() routine handles some special characters that are not included in the international morse aplhabet. Characters are then played by calling the genmorse() routine.
static void
playchar (char c)
{
short buf[16 * BUFSZ];
int l;
l = 0;
if (c <= 'Z' && c >= 'A')
c += 32;
switch (c)
{
case '\n':
return;
break;
case ' ':
case '\t':
l = genmorse (buf, ' ');
break;
case '\r':
break;
case 'Å':
l = genmorse (buf, 'å');
break;
case 'Ä':
l = genmorse (buf, 'ä');
break;
case 'Ö':
l = genmorse (buf, 'ö');
break;
case 'Ü':
l = genmorse (buf, 'ü');
break;
default:
l = genmorse (buf, c);
}
write (audiofd, buf, 2 * l);
if (2 * l < charsize)
{
char tmp[4 * 1024 * 1024];
l = charsize - 2 * l;
memset (tmp, 0, l);
write (audiofd, tmp, l);
}
}
int
main (int argc, char *argv[])
{
char *devname = "/dev/dsp";
short buf[16 * BUFSZ];
char line[1024];
int i, parm;
int l, speed, charspeed, wpm = 8;
Charcter rate (CPS/WPS) handling.
if (argc > 1)
{
wpm = atoi (argv[1]);
if (wpm == 0)
wpm = 12;
}
if (argc > 2)
charspeed = atoi (argv[2]);
speed = wpm;
charsize = 60 * SRATE * 2 / charspeed;
printf ("Words per minute %d. Characters per minute %d\n", wpm, wpm * 5);
printf ("Charrate %d chars/min -> (%d samples)\n", charspeed, charsize);
dotsize = SRATE / speed;
ncodes = strlen (Chars);
Open the audio device and set up the parameters.
if ((audiofd = open (devname, O_WRONLY, 0)) == -1)
{
perror (devname);
exit (-1);
}
parm = AFMT_S16_LE;
if (ioctl (audiofd, SNDCTL_DSP_SETFMT, &parm) == -1)
{
perror ("SETFMT");
close (audiofd);
exit (-1);
}
if (parm != AFMT_S16_LE)
{
printf
("Error: 32/24 bit sample format is not supported by the device\n");
printf ("%08x/%08x\n", parm, AFMT_S16_LE);
close (audiofd);
exit (-1);
}
parm = SRATE;
if (ioctl (audiofd, SNDCTL_DSP_SPEED, &parm) == -1)
{
perror ("SPEED");
close (audiofd);
exit (-1);
}
if (parm != SRATE)
{
printf
("Error: %d Hz sampling rate is not supported by the device (%d)\n",
SRATE, parm);
close (audiofd);
exit (-1);
}
The setup phase is complete. After this moment we can forget that we are working on a device. The remainder of this program behaves just like it's writing to any (disk) file.
a = 0.0;
step = 360.0 * 600.0 / parm;
l = 0;
l += genpulse (&buf[l], 1, 0);
write (audiofd, buf, l * 2);
/* Some initial delay */
memset (buf, 0, 4096);
for (l = 0; l < 30; l++)
write (audiofd, buf, 4096);
while (fgets (line, sizeof (line), stdin) != NULL)
{
if (*line == '#')
continue;
for (i = 0; i < strlen (line); i++)
{
playchar (line[i]);
}
}
/* Some final delay */
memset (buf, 0, 4096);
for (l = 0; l < 20; l++)
write (audiofd, buf, 4096);
close (audiofd);
exit (0);
}