Hi, Thank you for your quick respond. Regarding 2 and 3 below, aren't those different names for the same thing? If not, can you give me an example of a case where they are different? Thanks. -----Original Message----- From: Clemens Ladisch [mailto:cladisch@xxxxxxxxxxxx] Sent: Thursday, October 19, 2006 11:23 AM To: Assaf Hoffman; alsa-devel@xxxxxxxxxxxxxxxxxxxxx Cc: Rita Shtern Subject: Re: ALSA supported PCM formats Importance: Low Assaf Hoffman wrote: > I'm new to ALSA and I'm trying to understand the PCM formats and the way > ALSA stack place/pick them from the DMA buffer. > > My understanding concerns PCM formats that their physical representation > bit size is bigger than the actual sound sample bit size. > For example, defined in pcm_misc.c file under pcm_formats[]: > [SNDRV_PCM_FORMAT_x24_xE] = {.width = 24, .phys = 32, ...} > [SNDRV_PCM_FORMAT_x20_3xE] = {.width = 20, .phys = 24, ...} > [SNDRV_PCM_FORMAT_x18_3xE] = {.width = 18, .phys = 24, ...} > How the ALSA stack (kernel 2.6.12.6) knows the offset of the sound > sample bits inside the format physical size? For example, when the sound > sample size is 24 (.width = 24) and the format physical size is 32 > (.phys = 32) the sound sample offset inside the physical frame can > anywhere beteen 0-7 bit. How the ALSA stack can know where to look for > the sound sample? There are three sizes that describe a sample: 1) physical size: how many bits are occupied in memory, i.e., how many data is read from/written to the DMA buffer for each sample; 2) sample width: the number of bits, starting at the _least_ significant bit inside (1), used for sample data; 3) significant bits: the number of bits, starting at the _most_ significant bit inside (2), actually used for sample data. Which bit is least/most significant depends on whether the sample format is little or big endian. HTH Clemens ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-devel
