Bug in the generation of IEC958 subframes

[Nicolas Boullis <nboullis@debian.org>]

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Hi,

While working on an ALSA driver for the audio part of em8300-based MPEG 
decoder boards (Sigma Designs' Hollywood+ boards and Creative Labs' DXR3 
boards), I think I discovered a bug in the code that generates IEC958 
subframes from linear samples (iec958 plugin): M and W preambles are 
swapped, and B preambles should only be used on even subframes. The 
attached patch fixes this issue.

Moreover, (using debian's 1.0.9-3 package, I haven't checked with 
1.0.10rc3), I get segfaults whenever I try to specify the preambles in 
my ~/.asoundrc file.

(https://bugtrack.alsa-project.org/alsa-bug/ times out, that's why I'm 
sending this report here.)


Cheers,

Nicolas

PS: please CC replies to me, as I don't read the alsa-devel ML.

[-- Attachment #2: alsa-lib.patch --]
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diff -ruN alsa-lib-1.0.10rc3.orig/src/pcm/pcm_iec958.c alsa-lib-1.0.10rc3/src/pcm/pcm_iec958.c
--- alsa-lib-1.0.10rc3.orig/src/pcm/pcm_iec958.c	2005-05-24 16:14:35.000000000 +0200
+++ alsa-lib-1.0.10rc3/src/pcm/pcm_iec958.c	2005-11-16 01:35:46.000000000 +0100
@@ -116,10 +116,10 @@
 		data |= 0x80000000;
 
 	/* Preamble */
-	if (! iec->counter)
-		data |= iec->preamble[PREAMBLE_Z];	/* Block start, 'Z' */
-	else if (! channel)
+	if (channel)
 		data |= iec->preamble[PREAMBLE_Y];	/* odd sub frame, 'Y' */
+	else if (! iec->counter)
+		data |= iec->preamble[PREAMBLE_Z];	/* Block start, 'Z' */
 	else
 		data |= iec->preamble[PREAMBLE_X];	/* even sub frame, 'X' */