On Jun 12 2016 17:28, Henrik Austad wrote: > On Sun, Jun 12, 2016 at 12:38:36PM +0900, Takashi Sakamoto wrote: >> I'm one of maintainers for ALSA firewire stack, which handles IEC >> 61883-1/6 and vendor-unique packets on IEEE 1394 bus for consumer >> recording equipments. >> (I'm not in MAINTAINERS because I'm a shy boy.) >> >> IEC 61883-6 describes that one packet can multiplex several types of >> data in its data channels; i.e. Multi Bit Linear Audio data (PCM >> samples), One Bit Audio Data (DSD), MIDI messages and so on. > > Hmm, that I did not know, not sure how that applies to AVB, but definately > something I have to look into. For your information, I describe more about it. You can see pre-standardized specification for IEC 61883-6 in website of 1394 Trade Association. Let's look for 'Audio and Music Data Transmission Protocol 2.3 (October 13, 2010, 1394TA)' http://1394ta.org/specifications/ In 'clause 12. AM824 SEQUENCE ADAPTATION LAYERS', you can see that one data block includes several types of data. But I can imagine that joint group for AVB loosely refers to IEC 61883-6. In this case, AVB specification might describe one data block transfers one type of data, to drop unreasonable complexities. >> If you handles packet payload in 'struct snd_pcm_ops.copy', a process >> context of an ALSA PCM applications performs the work. Thus, no chances >> to multiplex data with the other types. > > The driver is not adhering fully to any standards right now, the amount of > detail is quite high - but I'm slowly improving as I go through the > standards. Getting on top of all the standards and all the different > subsystems are definately a work in progress (it's a lot to digest!) In my taste, the driver is not necessarily compliant to any standards. It's enough just to work its task, without bad side-effects to Linux system. Based on this concept, current ALSA firewire stack just support PCM frames and MIDI messages. Here, I tell you that actual devices tend not to be compliant to any standards and lost inter-operability. (Especially, most of audio and music units on IEEE 1394 bus ignores some of items in standards. In short, they already lost inter-operability.) So here, we just consider about what actual devices do, instead of following any standards. Regards Takashi Sakamoto
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