Date   : Mon, 06 Jul 2009 09:07:44 +0100
From   : philb@... (Phil Blundell)
Subject: econet bridge protocol

On Mon, 2009-07-06 at 00:45 +0200, Johan Heuseveldt wrote:
> The problem I encountered during reverse engeneering the PCB
> for a schematic, was seeing some wires of the two networks
> connected together, leaving me completely baffeled, as it suggests
> a hardware connection too between the two networks???
> (I must be overlooking something here)

That does sound fairly implausible.  Obviously the drain wires would be
connected together but I don't think there should be any other direct
electrical connection between the two networks.  Which wires did you
find to be joined together?

> About a disassembly, I should be able to generate one automatically.
> If needed, wanted, makes one of you happy...

John Kenyon sent me a copy of his disassembly which seems to be fairly
complete.  (Thanks, John.)  So, there's probably no need to generate
another.

> I have several bridges; 2x Acorn, 1x SJResearch, but I have no clue
> how to capture these packets. In case you have specific sw to do so,
> let me know off list. Using Netmon is doable, but needs a lot of know
> how and expertise knowing where to look for, and how to interpret the
> data I guess.
> (and Netmon does /not/ show /all/ the data!)

If you felt like conducting a couple of tests, some empirical results
might certainly be handy to confirm that I've understood the disassembly
correctly.

In particular, if you connect the three bridges in a chain, something
like:

net 1
|
Acorn bridge
|
net 2
|
SJ bridge
|
net 3
|
Acorn bridge
|
net 4

and then capture a packet trace on net #3 while power-cycling the bridge
between 1 and 2, that might be useful.  More or less any network monitor
is probably good enough for this; I mostly use either NETMON on a BBC,
or my own RISC OS monitor on an A5000.  Bridge packets tend just to be
broadcasts of a couple of bytes so you don't need any sophisticated
monitoring technology :-)

p.