modified version of pyalsaaudio module

py/CHANGES

@@ -1,3 +1,15 @@
+Version 0.8.6:
+- Added four methods to the 'PCM' class to allow users to get detailed information about the device:
+
+  - 'getformats()' returns a dictionary of name / value pairs, one for each of the card's
+    supported formats - e.g. '{"U8": 1, "S16_LE": 2}',
+  - 'getchannels()' returns a list of the supported channel numbers, e.g. '[1, 2]',
+  - 'getrates()' returns supported sample rates for the device, e.g. '[48000]',
+  - 'getratebounds()' returns the device's official minimum and maximum supported 
+    sample rates as a tuple, e.g. '(4000, 48000)'.
+  
+  (contributed by @jdstmporter)
+
 Version 0.8.5:
 - Return an empty string/bytestring when 'read()' detects an 
   overrun. Previously the returned data was undefined (contributed by @jcea)

py/alsaaudio.c

@@ -29,6 +29,64 @@
 #include <alsa/version.h>
 #include <stdio.h>
 
+#define ARRAY_SIZE(a) (sizeof(a) / sizeof *(a))
+static const snd_pcm_format_t ALSAFormats[] = {
+		SND_PCM_FORMAT_S8,
+		SND_PCM_FORMAT_U8,
+		SND_PCM_FORMAT_S16_LE,
+		SND_PCM_FORMAT_S16_BE,
+		SND_PCM_FORMAT_U16_LE,
+		SND_PCM_FORMAT_U16_BE,
+		SND_PCM_FORMAT_S24_LE,
+		SND_PCM_FORMAT_S24_BE,
+		SND_PCM_FORMAT_U24_LE,
+		SND_PCM_FORMAT_U24_BE,
+		SND_PCM_FORMAT_S32_LE,
+		SND_PCM_FORMAT_S32_BE,
+		SND_PCM_FORMAT_U32_LE,
+		SND_PCM_FORMAT_U32_BE,
+		SND_PCM_FORMAT_FLOAT_LE,
+		SND_PCM_FORMAT_FLOAT_BE,
+		SND_PCM_FORMAT_FLOAT64_LE,
+		SND_PCM_FORMAT_FLOAT64_BE,
+		SND_PCM_FORMAT_IEC958_SUBFRAME_LE,
+		SND_PCM_FORMAT_IEC958_SUBFRAME_BE,
+		SND_PCM_FORMAT_MU_LAW,
+		SND_PCM_FORMAT_A_LAW,
+		SND_PCM_FORMAT_IMA_ADPCM,
+		SND_PCM_FORMAT_MPEG,
+		SND_PCM_FORMAT_GSM,
+		SND_PCM_FORMAT_SPECIAL,
+		SND_PCM_FORMAT_S24_3LE,
+		SND_PCM_FORMAT_S24_3BE,
+		SND_PCM_FORMAT_U24_3LE,
+		SND_PCM_FORMAT_U24_3BE,
+		SND_PCM_FORMAT_S20_3LE,
+		SND_PCM_FORMAT_S20_3BE,
+		SND_PCM_FORMAT_U20_3LE,
+		SND_PCM_FORMAT_U20_3BE,
+		SND_PCM_FORMAT_S18_3LE,
+		SND_PCM_FORMAT_S18_3BE,
+		SND_PCM_FORMAT_U18_3LE,
+		SND_PCM_FORMAT_U18_3BE
+};
+static const unsigned ALSARates[] = {
+		4000,
+		5512,
+		8000,
+		11025,
+		16000,
+		22050,
+		32000,
+		44100,
+		48000,
+		64000,
+		88200,
+		96000,
+		176400,
+		192000
+};
+
 PyDoc_STRVAR(alsaaudio_module_doc,
              "This modules provides support for the ALSA audio API.\n"
              "\n"
@@ -572,6 +630,169 @@ alsapcm_dumpinfo(alsapcm_t *self, PyObject *args)
     return Py_None;
 }
 
+// auxiliary function
+
+
+static PyObject *
+alsapcm_getformats(alsapcm_t *self, PyObject *args) {
+	snd_pcm_t *pcm = self->handle;
+		if (!pcm) {
+			PyErr_SetString(ALSAAudioError, "PCM device is closed");
+		    return NULL;
+		}
+		snd_pcm_hw_params_t *params;
+		snd_pcm_hw_params_alloca(&params);
+		int err = snd_pcm_hw_params_any(pcm, params);
+		if (err < 0) {
+			PyErr_SetString(ALSAAudioError, "Cannot get hardware parameters");
+			return NULL;
+		}
+
+	PyObject *fmts = PyDict_New();
+	for (int i = 0; i < ARRAY_SIZE(ALSAFormats); ++i) {
+		snd_pcm_format_t format = ALSAFormats[i];
+		if (!snd_pcm_hw_params_test_format(pcm, params, format)) {
+			const char *name = snd_pcm_format_name(format);
+			PyObject *pname=PyUnicode_FromString(name);
+			PyObject *value=PyLong_FromLong((long)format);
+			PyDict_SetItem(fmts,pname,value);
+		}
+	}
+	return fmts;
+}
+
+PyDoc_STRVAR(getformats_doc,
+"getformats() -> [str:int]\n\
+\n\
+Returns dictionary of supported format codes keyed by their standard ALSA names.");
+
+static PyObject *
+alsapcm_getratemaxmin(alsapcm_t *self, PyObject *args) {
+	snd_pcm_t *pcm = self->handle;
+	if (!pcm) {
+		PyErr_SetString(ALSAAudioError, "PCM device is closed");
+	    return NULL;
+	}
+	snd_pcm_hw_params_t *params;
+	snd_pcm_hw_params_alloca(&params);
+	int err = snd_pcm_hw_params_any(pcm, params);
+	if (err < 0) {
+		PyErr_SetString(ALSAAudioError, "Cannot get hardware parameters");
+		return NULL;
+	}
+	unsigned min,max;
+	if(snd_pcm_hw_params_get_rate_min(params, &min,NULL)<0) {
+		PyErr_SetString(ALSAAudioError, "Cannot get minimum supported bitrate");
+		return NULL;
+	}
+	if(snd_pcm_hw_params_get_rate_max(params, &max,NULL)<0) {
+		PyErr_SetString(ALSAAudioError, "Cannot get maximum supported bitrate");
+		return NULL;
+	}
+	PyObject *minp=PyLong_FromLong(min);
+	PyObject *maxp=PyLong_FromLong(max);
+	return PyTuple_Pack(2,minp,maxp);
+}
+
+PyDoc_STRVAR(getratebounds_doc,
+"getratebounds() -> (int,int)\n\
+\n\
+Returns the card's minimum and maximum supported sample rates as a tuple.");
+
+static PyObject *
+alsapcm_getrates(alsapcm_t *self, PyObject *args) {
+	snd_pcm_t *pcm = self->handle;
+	if (!pcm) {
+		PyErr_SetString(ALSAAudioError, "PCM device is closed");
+	    return NULL;
+	}
+	snd_pcm_hw_params_t *params;
+	snd_pcm_hw_params_alloca(&params);
+	int err = snd_pcm_hw_params_any(pcm, params);
+	if (err < 0) {
+		PyErr_SetString(ALSAAudioError, "Cannot get hardware parameters");
+		return NULL;
+	}
+	unsigned min,max;
+	if(snd_pcm_hw_params_get_rate_min(params, &min,NULL)<0) {
+		PyErr_SetString(ALSAAudioError, "Cannot get minimum supported bitrate");
+		return NULL;
+	}
+	if(snd_pcm_hw_params_get_rate_max(params, &max,NULL)<0) {
+		PyErr_SetString(ALSAAudioError, "Cannot get maximum supported bitrate");
+		return NULL;
+	}
+	if(min==max) {
+		return PyLong_FromLong(min);
+	}
+	else if(!snd_pcm_hw_params_test_rate(pcm, params, min + 1, 0)) {
+		PyObject *minp=PyLong_FromLong(min);
+		PyObject *maxp=PyLong_FromLong(max);
+		return PyTuple_Pack(2,minp,maxp);
+	}
+	else {
+		PyObject *rates=PyList_New(0);
+		for(int i=0;i<ARRAY_SIZE(ALSARates);i++) {
+			unsigned rate=ALSARates[i];
+			if(!snd_pcm_hw_params_test_rate(pcm, params, rate,0)) {
+				PyObject *prate=PyLong_FromLong(rate);
+				PyList_Append(rates,prate);
+			}
+		}
+		return rates;
+	}
+}
+
+PyDoc_STRVAR(getrates_doc,
+"getrates() -> obj\n\
+\n\
+Returns the sample rates supported by the device.\
+Returned value can be one of three types, depending on the card's properties.\
+There are three cases:\n\
+\n\
+- Card supports only a single rate: returns the rate\n\
+- Card supports a continuous range of rates: returns a tuple of the range's lower and upper bounds (inclusive)\n\
+- Card supports a collection of well-known rates: returns a list of the supported rates");
+
+static PyObject *
+alsapcm_getchannels(alsapcm_t *self,PyObject *args) {
+	snd_pcm_t *pcm = self->handle;
+		if (!pcm) {
+			PyErr_SetString(ALSAAudioError, "PCM device is closed");
+		    return NULL;
+		}
+		snd_pcm_hw_params_t *params;
+		snd_pcm_hw_params_alloca(&params);
+		int err = snd_pcm_hw_params_any(pcm, params);
+		if (err < 0) {
+			PyErr_SetString(ALSAAudioError, "Cannot get hardware parameters");
+			return NULL;
+		}
+	unsigned min,max;
+	if(snd_pcm_hw_params_get_channels_min(params, &min)<0) {
+			PyErr_SetString(ALSAAudioError, "Cannot get minimum supported number of channels");
+			return NULL;
+		}
+		if(snd_pcm_hw_params_get_channels_max(params, &max)<0) {
+			PyErr_SetString(ALSAAudioError, "Cannot get maximum supported number of channels");
+			return NULL;
+		}
+
+		PyObject *out=PyList_New(0);
+
+		for(unsigned ch=min;ch<=max;++ch) {
+			if (!snd_pcm_hw_params_test_channels(pcm, params, ch)) {
+				PyObject *pch=PyLong_FromLong(ch);
+				PyList_Append(out,pch);
+			}
+		}
+		return out;
+}
+PyDoc_STRVAR(getchannels_doc,
+"getchannels() -> [int]\n\
+\n\
+Returns list of supported channel numbers.");
+
 static PyObject *
 alsapcm_pcmtype(alsapcm_t *self, PyObject *args)
 {
@@ -1101,6 +1322,10 @@ static PyMethodDef alsapcm_methods[] = {
     {"setperiodsize", (PyCFunction)alsapcm_setperiodsize, METH_VARARGS,
      setperiodsize_doc},
     {"dumpinfo", (PyCFunction)alsapcm_dumpinfo, METH_VARARGS},
+	{"getformats", (PyCFunction)alsapcm_getformats, METH_VARARGS, getformats_doc},
+	{"getratebounds", (PyCFunction)alsapcm_getratemaxmin, METH_VARARGS, getratebounds_doc},
+	{"getrates", (PyCFunction)alsapcm_getrates, METH_VARARGS, getrates_doc},
+	{"getchannels", (PyCFunction)alsapcm_getchannels, METH_VARARGS, getchannels_doc},
     {"read", (PyCFunction)alsapcm_read, METH_VARARGS, read_doc},
     {"write", (PyCFunction)alsapcm_write, METH_VARARGS, write_doc},
     {"pause", (PyCFunction)alsapcm_pause, METH_VARARGS, pause_doc},

py/setup.py

@@ -8,7 +8,7 @@ from setuptools import setup
 from setuptools.extension import Extension
 from sys import version
 
-pyalsa_version = '0.8.5'
+pyalsa_version = '0.8.6'
 
 if __name__ == '__main__':
     setup(

tests/params.c

@@ -59,6 +59,7 @@ static const snd_pcm_format_t formats[] = {
 };
 
 static const unsigned int rates[] = {
+		4000,
 		5512,
 		8000,
 		11025,
@@ -164,7 +165,7 @@ int main(int argc, char *argv[])
 
 	printf("Formats:");
 	for (int i = 0; i < info.nFormats; ++i) {
-		printf(" %s", snd_pcm_format_name(formats[i]));
+		printf("%s ", snd_pcm_format_name(info.formats[i]));
 	}
 	putchar('\n');
 	printf("Rates:");
@@ -178,7 +179,7 @@ int main(int argc, char *argv[])
 		printf(" %u", info.channels[i]);
 	}
 	putchar('\n');
-	/*
+
 
 	err = snd_pcm_open(&pcm, device_name, SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK);
 	if (err < 0) {
@@ -205,8 +206,10 @@ int main(int argc, char *argv[])
 
 	printf("Formats:");
 	for (i = 0; i < ARRAY_SIZE(formats); ++i) {
-		if (!snd_pcm_hw_params_test_format(pcm, hw_params, formats[i]))
+		if (!snd_pcm_hw_params_test_format(pcm, hw_params, formats[i])) {
 			printf(" %s", snd_pcm_format_name(formats[i]));
+		}
+
 	}
 	putchar('\n');
 
@@ -289,7 +292,7 @@ int main(int argc, char *argv[])
 
 	snd_pcm_close(pcm);
 
-	 */
+
 	return 0;
 }