[sdiy] ADDA & MIDI over Ethernet (long)

[j vallier]

Achim,

>
>I've looked at both mLAN and MaGIC and both seem to be needlessly
>complicated if not to say bloated. I'll have to think about this some
>more...

You are right--these specs (and others) are quite complex--what you see as 
"needlessly bloated" is the fact that these full specifications need to be 
"everything to everybody" and get rather involved (ever try reading the 
802.11 spec???) What you may not immediately see is that these protools need 
to be somewhat complex to guarantee the following:

1. Audio/control packet is sent and received in the right order
2. Audio/control packet is sent and received in a time frame where there's 
no audible delay (latency)
3. Audio/control packet arrives at it's intended destination at all (quality 
of service (QOS))
4. Control of Jitter in the audio frame

you obvuiosly can tell the consequrnces of these conditions not being met. 
Sending a packet of data out a PC's ethernet port is trivial; ensuring 
latency, QOS, and jitter is a completely different issue and is the reason 
we don't just use our plain-vanilla ethernet port on our computers for this 
purpose (mainly due to TCP/IP issues). A lot of these companies spend 
millions of dollars and countless man-hours on developing these 
technologies, so unfortately it is not in the realm of DIY yet, or at least 
until chipsets/IP becomes available to hack (which will be fun).

What is perhaps not so obvious from these specs is that you can certainly 
implement a SUBSET of the specification  as long as it meets your needs. For 
example, a simple MaGIC engine can reside in a Xilinx Spartan 2S50 FPGA, 
providing a simple data pipe with 32-bit parallel interfaces on either side 
and connect to the uP of your choice, allowing you to get as fancy as you 
wish with the packet contents. Xilinx may provide this core as IP in the 
future, in the meantime some reasonable VHDL/Verilog chops can overcome the 
challenge. This is probably closer to what you were originally looking 
for... The French company Digigram has already done this with their 
"Etherspeaker" technology--perhaps you can hack that HW as well.

You asked a good questions on this. I hope I shed some light on them.

Peff

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