On 16.07.2017 02:13, Len Ovens wrote:
> On Sat, 15 Jul 2017, Bearcat Şándor wrote:
>
>> Ahh, i was misunderstanding. I was under the impression that i could just put an
>> extra 2 ethernet ports into my computer, install the kernel drivers and libraries
>> (when they're available) and have an operational Ravenna input/output. However,
>> if it needs a wordclock then it obviously needs a card. I had thought that the
>> 'wordclock' was part of the data packet.
>
> It is not word clock. but wall clock with high accuracy so word clock can be
> derived. It is possible to do an end point without by treating packets in the
> same way as as buffer in an audio card where alsa does not have to be aware of
> the exact clock rise or fall to deal with it. However, If you wish to send audio
> from an internal audio card to any aes67 endpoint. Your computer must be able to
> be provide an ntp server with good enough accuracy to provide wordclock to both
> your internal audio ai and to act as a master clock on the network... or be able
> to sync your internal audio card to an external ntp server. This accuracy pretty
> much requires a HW ntp server. As I said the intel i210 ethernet cards at
> $60-ish seems to be about the cheapest route.
>
> Depending on how synced you want things... SRC can do a very good job and the
> broadcast industry uses it a lot. The zita-njbridge does a great job of
> connecting two computers together and I suspect using the zita src library as
> part of an aes67 driver would make <whatever> ethernet card workable so long as
> the computer was never expected to be a master clock. So an aes67 network with
> only two linux computers may not be usable or at least your network would not be
> wholely aes67 compliant. An endpoint with no ntp able to follow a masterclock
> closely doesn't seem fully compliant to me from what I have read. So the windows
> drivers downloadable from various places would have the same problem of not
> being fully compliant too. Some of the MacOS hw does have an ethernet chip with
> builtin ntp server.
>
> So a driver that does what the windows driver does should be possible.
It think it should be PTP [1] instead of NTP above, the latter is not accurate
enough.
PTP can also be run in software timestamping mode, hardware timestamping will be
more accurate, though [2].
[1] https://en.wikipedia.org/wiki/Precision_Time_Protocol
[2] http://linuxptp.sourceforge.net/
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Received on Sun Jul 16 12:15:01 2017
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