Date   : Fri, 29 Jul 2005 18:39:44 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Econet-Ethernet bridge

On Fri, 2005-07-29 at 18:28 +0100, Rob wrote:
> At 16:14 29/07/2005, Johan Heuseveldt wrote:
> 
> >Hi Jules,
> >
> >On Fri 29 Jul, Jules Richardson wrote:
> >
> >[snip]
> >
> > >
> > > Does it actually have to do much though? I mean isn't functionality just
> > > a case of watching packets on each network interface and if they're not
> > > destined for that interface, write them out to the other interface?  I'm
> > > surprised much memory's needed to do that.
> >
> >The nets can have different speeds setup for their clocks.
> >
> >   1 From hi to lo speed you need you need some queue, possibly
> >      still sending;
> >   2 From lo to hi speed you need the store the data completely, and
> >      after being complete, it can be send
> >
> >  1 is a bit complicated in comparison with 2, and
> >  2 can't use the technique of 1
> >
> >  perhaps both use the technique or 2, so only one protocol is needed.
> >  It does puts both nets on hold for longer periods between the frames
> >  in the 4-way handshake, than without bridge.
> >
> >TBH, I don't how how it is really happening, but because of different
> >speeds between the nets, it isn't as simple as you thought! :-)
> >Time to invetigate the ROM code.
> 
> I imagine it'd also be pretty common for an incoming packet to have to be 
> queued simply because the destination network was currently in use (perhaps 
> by a 20K *view packet...) and it had to wait for the network to be free again..

I hadn't thought about the different network speeds (duh!) - but I
wonder if the bridge bothers with the hassle of queing stuff up until
the destination network's free. Depends on the higher protocols probably
and whether the sending station will timeout eventually if it gets no
ack from its transmissted packet...

> Now ... can a 6502 drive that ISA based ethernet chip that was being talked 
> about?

I'm glad I'm not the only one thinking that. A 6502-based gateway would
be rather cool :) I've certainly got spare 6502 CPUs, ROM and RAM chips
lying around here doing nothing (and a programmer). Or, failing that,
what about hacking the ethernet chip onto the 1MHz bus of a standard
beeb and just fitting it with a custom ROM? Saves a lot of building
work!

cheers

Jules