[alsa-devel] [RFC] G.723-24 format patch

[Ben Collins]

I'm writing a driver for a card that only has hardware support for
G.723-24 ADPCM format. I am working around the lack of support in alsa
at the moment for this format, but wanted to take a crack at
implementing it properly.

G.723-24 is a 3-bit signed sample at a fixed 8khz mono sample rate
(24000 bit rate). Basically means you need to take in at least 3 bytes
(8 samples) minimum for processing the standard packed version.

I don't have hardware that supports it, but since I was in the code, I
added a G723_24_1B format for producing 1 sample per byte (3 lower bits
are actual sample), but for my use I am producing the standard packed
stream.

Only question I had is that since this is signed, should I expect or
want the _1B version to be a 1 byte sign extended version of the 3-bit
sample, or just expect the lower 3 bits of the byte to be the g723-24
sample? Looking at other unpacked examples, I assume the latter rather
than the former.

diff --git a/include/sound/asound.h b/include/sound/asound.h
index 1f57bb9..16fc633 100644
--- a/include/sound/asound.h
+++ b/include/sound/asound.h
@@ -212,7 +212,9 @@ typedef int __bitwise snd_pcm_format_t;
 #define	SNDRV_PCM_FORMAT_S18_3BE	((__force snd_pcm_format_t) 41)	/* in three bytes */
 #define	SNDRV_PCM_FORMAT_U18_3LE	((__force snd_pcm_format_t) 42)	/* in three bytes */
 #define	SNDRV_PCM_FORMAT_U18_3BE	((__force snd_pcm_format_t) 43)	/* in three bytes */
-#define	SNDRV_PCM_FORMAT_LAST		SNDRV_PCM_FORMAT_U18_3BE
+#define	SNDRV_PCM_FORMAT_G723_24	((__force snd_pcm_format_t) 44) /* 8 samples in 3 bytes */
+#define	SNDRV_PCM_FORMAT_G723_24_1B	((__force snd_pcm_format_t) 45) /* 1 sample in 1 byte */
+#define	SNDRV_PCM_FORMAT_LAST		SNDRV_PCM_FORMAT_G723_24_1B
 
 #ifdef SNDRV_LITTLE_ENDIAN
 #define	SNDRV_PCM_FORMAT_S16		SNDRV_PCM_FORMAT_S16_LE
diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index de6d981..031e2cd 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -173,6 +173,8 @@ struct snd_pcm_ops {
 #define SNDRV_PCM_FMTBIT_U18_3LE	(1ULL << SNDRV_PCM_FORMAT_U18_3LE)
 #define SNDRV_PCM_FMTBIT_S18_3BE	(1ULL << SNDRV_PCM_FORMAT_S18_3BE)
 #define SNDRV_PCM_FMTBIT_U18_3BE	(1ULL << SNDRV_PCM_FORMAT_U18_3BE)
+#define SNDRV_PCM_FMTBIT_G723_24	(1ULL << SNDRV_PCM_FORMAT_G723_24)
+#define SNDRV_PCM_FMTBIT_G723_24_1B	(1ULL << SNDRV_PCM_FORMAT_G723_24_1B)
 
 #ifdef SNDRV_LITTLE_ENDIAN
 #define SNDRV_PCM_FMTBIT_S16		SNDRV_PCM_FMTBIT_S16_LE
diff --git a/sound/core/pcm_misc.c b/sound/core/pcm_misc.c
index ea2bf82..c7f8da4 100644
--- a/sound/core/pcm_misc.c
+++ b/sound/core/pcm_misc.c
@@ -128,6 +128,10 @@ static struct pcm_format_data pcm_formats[SNDRV_PCM_FORMAT_LAST+1] = {
 		.width = 4, .phys = 4, .le = -1, .signd = -1,
 		.silence = {},
 	},
+	[SNDRV_PCM_FORMAT_G723_24] = {
+		.width = 3, .phys = 3, .le = -1, .signd = 1,
+		.silence = {},
+	},
 	/* FIXME: the following three formats are not defined properly yet */
 	[SNDRV_PCM_FORMAT_MPEG] = {
 		.le = -1, .signd = -1,
@@ -186,6 +190,10 @@ static struct pcm_format_data pcm_formats[SNDRV_PCM_FORMAT_LAST+1] = {
 		.width = 18, .phys = 24, .le = 0, .signd = 0,
 		.silence = { 0x02, 0x00, 0x00 },
 	},
+	[SNDRV_PCM_FORMAT_G723_24_1B] = {
+		.width = 3, .phys = 8, .le = -1, .signd = 1,
+		.silence = {},
+	},
 };