Hi, Thank you for your reply. I would be happy if you kindly reply to the following questions: 1) According to your experience, is it correct to assume that once a PCM instance for playback/capture is prepared and triggered, the user data and channel status are constants during data transmit/receive? 2) In the case HW saves the user data and channel status in its internal registers, how would the ALSA stack know of any of them changed? 3) Is there a bridge application in the ALSA stack (kerne)? I mean, in case I would like to capture ICE958 frames and route them to ICE958 playback channel. Thanks. -----Original Message----- From: James Courtier-Dutton [mailto:James@xxxxxxxxxxxxxx] Sent: Wednesday, October 11, 2006 5:01 PM To: Assaf Hoffman Cc: alsa-devel@xxxxxxxxxxxxxxxxxxxxx; Rita Shtern Subject: Re: ALSA snd_xferi_t buffer arrangment Assaf Hoffman wrote: > Hi, > Thanks again for clear answers. > In case the HW strip the IEC958 frames, where the ALSA stack expect to > find the various frame data fields such as perr, valid bit, audio > sample, user data and channel status? Is there a data structure the HW > should follow when DMAing the striped data to the DRAM buffer? > What do you think of such acceleration? Does this saves a significant > CPU time processing the ICE958 frames? > Many thanks. > P.S. > I was looking into the ASLA stack and I could find > SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_XX only in snd_pcm_hardware structure > initialization. I could not see where it is used to tell the ALSA to > process the data as IEC958 frames. > A majority of sound cards strip the frame, and only put the audio samples in the DMA buffer. The sound card then stores the valid bits, non-audio bit, user data etc. in a separate register on the sound card. The processing of the IEC958 frames is done in alsa-lib. ALSA has two parts, and kernel part, and a user space lib. The kernel part does as little as possible, with the user space part doing all the format conversion etc. I have not looked closely, but I don't know if the alsa-lib decodes the IEC958 frames or not yet. James ------------------------------------------------------------------------- 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
