linuxaudio.org

Lorenzo:

quoted text
> >> Recent discussion on LAU morphed into an idea for an Ethernet

> >> driven sound card, and as this is now becoming a real

> >> development

> So I will plug this into my ethernet and have < 1ms latency? :)

The "this" part is currently only in our minds for the moment, but if

you solve the issue of connecting our "minds" to your ethernet port,

I'll solve the 1ms latency part :)
A simple ping:
  $ ping granat

  PING granat.lcl.aspodata.se (192.168.93.37) 56(84) bytes of data.

  64 bytes from granat.lcl.aspodata.se (192.168.93.37): icmp_seq=1 ttl=15 time=0.758 ms
gives me a round trip of < 1ms, so it should be possible.
So the time from analog, pushing out samples from the sender port,

till it is received the receiver port would be lower bounded by:
 sample conversion time

 lcl transport time to cpu

 cpu processing

 cpu to ethernet tranceiver

 ethernet preamble (assume quiet net)

 cable delay

 packet bit speed * packet length
Add to this any processing on the receiving side.
To help achieve low (network) latency one can:
. set up fixed arp entries (see arp(8))

. use fixed ip-addresses, no dhcp, no mDNS, no autoconfiguration or

  other talky protocols

. don't mix other hosts on the lan, make it as quiet as possible

. no DNS, use /ets/hosts files

. if possible use a crossover cable [1]
What kind of latency do you think would be a goal to strive to ?
Regards,

/Karl
[1] http://en.wikipedia.org/wiki/Ethernet_crossover_cable
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Karl Hammar                    Asp