soundmodem patch for ALSA compatibility issues

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


Attached is the latest version I've worked up of a patch to the
soundmodem "alsaio.c" interface code.  It corrects (or compensates
for) a number of problems I've encountered in using the soundmodem
with a SignaLink USB sound interface, and which I suspect might also
affect other USB sound adapters.

The changes are as follows:

[1] The list of four "hw:" device IDs suggested by soundmodemconfig has
    been expanded, to include the corresponding "plughw:" devices. These
    refer to the same underlying hardware, but connect to the device via
    an ALSA plugin which can perform sample-rate conversion.

    Relevance: some (many?) USB sound adapters support different sets of
    sample rates for their input and output channels... and some even
    have completely disjoint rate sets (i.e. there's no single sample
    rate available for both input and output).  Currently, the AFSK
    soundmodem (at least) can't deal with devices whose drivers don't
    return the same sample rates in both directions.  Using "plughw:"
    gets around the problem, by doing software sample-rate conversion
    where necessary and allowing the soundmodem to use whatever
    interface sample rate it requests.  The "plughw:" rate converter
    seems to work well... unlike the one in the kernel OSS compatibility
    layer, which (in my experience) can corrupt the audio data rather
    badly.

[2] I've added error handling logic in the transmit and receive routines
    to deal with an EPIPE error, which indicates a transmit data
    underrun or a receive overrun.  These were very common (and fatal)
    on my system.  I suspect that input overruns are likely to affect
    anyone who uses a full-duplex sound card/driver on a half-duplex
    radio channel.

[3] I've added a bit of additional trace information to a few of the
    error-logging printouts, and added suppression for the "file
    descriptor is in the wrong state" error which can be expected
    to occur frequently in the end-of-transmit routine (this routine
    will tend to try to start the receive channel when it's already
    running... a harmless error which I don't think needs to be
    reported).

[4] Moved a couple of variables inside the #ifdef'ed block which
    uses them, in order to avoid a compile-time "unused variable"
    warning if this code isn't enabled.

This patch is against the alsaio.c routine which was distributed
in the Debian distro of soundmodem-0.10.  IIRC it does not reflect
any of the other patches against 0.10 that have been floating
around (but I could be wrong about that).

This patch is, of course, offered under the same GPL v2 terms as
the code it modifies.

Happy Holidays, all!

--- soundmodem-0.10/soundcard/alsaio.c	2004-04-13 08:05:51.000000000 -0700
+++ soundmodem-0.10-alsapatch/soundcard/alsaio.c	2008-12-25 19:02:02.000000000 -0800
@@ -75,7 +75,7 @@
 
 struct modemparams ioparams_alsasoundcard[] = {
 	{ "device", "ALSA Audio Driver", "Path name of the audio (soundcard) driver", "hw:0,0", MODEMPAR_COMBO, 
-	  { c: { { "hw:0,0", "hw:1,0", "hw:2,0", "hw:3,0" } } } },
+	  { c: { { "hw:0,0", "plughw:0,0", "hw:1,0", "plughw:1,0", "hw:2,0", "plughw:2,0", "hw:3,0", "plughw:3,0" } } } },
         { "halfdup", "Half Duplex", "Force operating the Sound Driver in Half Duplex mode", "0", MODEMPAR_CHECKBUTTON },
 	{ "capturechannelmode", "Capture Channel", "Capture Channel", "Mono", MODEMPAR_COMBO, 
 	  { c: { { "Mono", "Left", "Right" } } } },
@@ -348,21 +348,23 @@
 
 	err = snd_pcm_drain(audioio->playback_handle);
 	if (err < 0)
-		logprintf(MLOG_ERROR, "snd_pcm_drain: %s", snd_strerror(err));
+		logprintf(MLOG_ERROR, "snd_pcm_drain in iotxend: %s", snd_strerror(err));
 	if (!(audioio->flags & CAP_HALFDUPLEX))
 		return;
 	err = snd_pcm_start(audioio->capture_handle);
-	if (err < 0)
-		logprintf(MLOG_ERROR, "snd_pcm_start: %s", snd_strerror(err));
+	if (err < 0 && err != -EBADFD)
+		logprintf(MLOG_ERROR, "snd_pcm_start in iotxend: %s", snd_strerror(err));
 }
 
 static inline void iotxstart(struct audioio_unix *audioio)
 {
 	int err;
-
+	if (snd_pcm_prepare(audioio->playback_handle) < 0) {
+		logprintf(MLOG_ERROR, "Error preparing tx.\n");
+	}
 	err = snd_pcm_start(audioio->playback_handle);
 	if (err < 0)
-		logprintf(MLOG_ERROR, "snd_pcm_start: %s", snd_strerror(err));
+		logprintf(MLOG_ERROR, "snd_pcm_start in iotxstart: %s", snd_strerror(err));
 }
 
 /* ---------------------------------------------------------------------- */
@@ -390,6 +392,12 @@
 	if (!audioio->playback_handle)
 		return;
 	err = snd_pcm_writei(audioio->playback_handle, p, nr);
+	if (err == -EPIPE) {
+		if (snd_pcm_prepare(audioio->capture_handle) < 0) {
+			logprintf(MLOG_ERROR, "Error preparing tx.\n");
+		}
+		err = snd_pcm_writei(audioio->playback_handle, p, nr);
+	}
 	if (err < 0) {
 		logprintf(MLOG_ERROR, "audio: snd_pcm_writei: %s", snd_strerror(err));
 		return;
@@ -449,6 +457,12 @@
 		if (!audioio->capture_handle)
 			logerr(MLOG_FATAL, "audio: read: capture handle NULL");
 		i = snd_pcm_readi(audioio->capture_handle, ibuf, sizeof(ibuf)/sizeof(ibuf[0])/2);
+		if (i == -EPIPE) {
+			if (snd_pcm_prepare(audioio->capture_handle) < 0) {
+				logprintf(MLOG_ERROR, "Error preparing rx.\n");
+			}
+			i = snd_pcm_readi(audioio->capture_handle, ibuf, sizeof(ibuf)/sizeof(ibuf[0])/2);
+		}
 		if (i < 0)
 			logprintf(MLOG_FATAL, "audio: snd_pcm_readi: %s", snd_strerror(i));
 		if (!i) {
@@ -560,10 +574,10 @@
 static void iotransmitstop(struct audioio *aio)
 {
 	struct audioio_unix *audioio = (struct audioio_unix *)aio;
-	short sbuf[256];
-	unsigned int i, j;
 
 #if 0
+	short sbuf[256];
+	unsigned int i, j;
 	/* add 20ms tail */
 	i = audioio->samplerate / 50;
 	memset(sbuf, 0, sizeof(sbuf));

[Linux Newbie]     [Kernel Newbies]     [Memory]     [Git]     [Security]     [Netfilter]     [Linux Admin]     [Bugtraq]     [Photo]     [Yosemite Photos]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [ARM Linux Kernel]     [Linux Networking]     [Linux Security]     [Linux RAID]     [Samba]     [Video 4 Linux]     [Linux Resources]

Add to Google Powered by Linux