000
22.07.2003, 14:31 Uhr
HeroHolger
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hallo.
ich hab ein Problem unter Linux mit Alsa 0.9 meine Soundkarte anzusteuern.
ich hab folgende Zeilen aus dem Alsa-How-To-Do genommen und gelinkt.
| C++: |
snd_pcm_t *pcm_handle;
snd_pcm_stream_t stream= SND_PCM_STREAM_PLAYBACK;
snd_pcm_hw_params_t *hwparams;
char *pcm_name;
/* Init pcm_name. Of course, later you */
/* will make this configurable ;-) */
pcm_name = strdup("plughw:0,0");
/* Allocate the snd_pcm_hw_params_t structure on the stack. */
snd_pcm_hw_params_alloca(&hwparams);
if (snd_pcm_open(&pcm_handle, pcm_name, stream, 0) < 0)
{
fprintf(stderr, "Error opening PCM device %s\n", pcm_name);
return(-1);
}
if (snd_pcm_hw_params_any(pcm_handle, hwparams) < 0)
{
fprintf(stderr, "Can not configure this PCM device.\n");
return(-1);
}
int rate = 44100; /* Sample rate */
int exact_rate; /* Sample rate returned by */
/* snd_pcm_hw_params_set_rate_near */
int dir; /* exact_rate == rate --> dir = 0 */
/* exact_rate < rate --> dir = -1 */
/* exact_rate > rate --> dir = 1 */
int periods = 2; /* Number of periods */
int periodsize = 8192; /* Periodsize (bytes) */
/* Set access type. This can be either */
/* SND_PCM_ACCESS_RW_INTERLEAVED or */
/* SND_PCM_ACCESS_RW_NONINTERLEAVED. */
/* There are also access types for MMAPed */
/* access, but this is beyond the scope */
/* of this introduction. */
if (snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0) {
fprintf(stderr, "Error setting access.\n");
return(-1);
}
/* Set sample format */
if (snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_S16_LE) < 0) {
fprintf(stderr, "Error setting format.\n");
return(-1);
}
/* Set sample rate. If the exact rate is not supported */
/* by the hardware, use nearest possible rate. */
exact_rate = snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, rate, &dir);
cout << "\n\n!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! " << dir << "\n\n";
if (dir != 0) {
fprintf(stderr, "The rate %d Hz is not supported by your hardware.\n==> Using %d Hz instead.\n", rate, exact_rate);
}
/* Set number of channels */
if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2) < 0) {
fprintf(stderr, "Error setting channels.\n");
return(-1);
}
/* Set number of periods. Periods used to be called fragments. */
if (snd_pcm_hw_params_set_periods(pcm_handle, hwparams, periods, 0) < 0) {
fprintf(stderr, "Error setting periods.\n");
return(-1);
}
/* Set buffer size (in frames). The resulting latency is given by */
/* latency = periodsize * periods / (rate * bytes_per_frame) */
if (snd_pcm_hw_params_set_buffer_size(pcm_handle, hwparams, (periodsize * periods)>>5) < 0) {
fprintf(stderr, "Error setting buffersize.\n");
return(-1);
}
/* Apply HW parameter settings to */
/* PCM device and prepare device */
if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) {
fprintf(stderr, "Error setting HW params.\n");
return(-1);
}
unsigned char *data;
int pcmreturn, l1, l2;
short s1, s2;
int frames;
data = (unsigned char *)malloc(periodsize);
frames = periodsize >> 2;
for(l1 = 0; l1 < 100; l1++) {
for(l2 = 0; l2 < frames; l2++) { //Veränderungen hier!!!!!!!!!!
s1 = (l2 % 128) * 100 - 5000;
s2 = (l2 % 256) * 100 - 5000;
data[4*l2] = (unsigned char)s1;
data[4*l2+1] = s1 >> 8;
data[4*l2+2] = (unsigned char)s2;
data[4*l2+3] = s2 >> 8;
}
while ((pcmreturn = snd_pcm_writei(pcm_handle, data, frames)) < 0) {
snd_pcm_prepare(pcm_handle);
fprintf(stderr, "<<<<<<<<<<<<<<< Buffer Underrun >>>>>>>>>>>>>>>\n");
}
}
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ich mußte, weil in der markierten Zeile(nach dem How-To) die Variable nicht deklariert war , die Variable "frames" entsprechend nutzen wie ich es gerade mache.
Kann mir irgendjemand erklären, warum ich immer einen Buffer-Underun bekomme. Normalerweise müßte es doch funktionieren.
mfg
Holger
Dieser Post wurde am 22.07.2003 um 14:36 Uhr von ao editiert. |
