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

[Takashi Iwai]

At Sat, 01 May 2010 11:36:03 -0400,
Ben Collins wrote:
> 
> 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.

I suppose both are non-linear formats, so you shouldn't give
signed/unsigned flags for them.  Otherwise snd_pcm_format_linear()
will return 1.

Other than that, addition of these new formats look good to me.


thanks,

Takashi


> 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 = {},
> +	},
>  };
>  
> 
> 
> 
> 
> 
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