Date   : Sun, 20 Jun 2004 11:57:40 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: PC/Econet

On Sun, 2004-06-20 at 10:45, Philip Blundell wrote:
> On Sun, 2004-06-20 at 10:40, Jules Richardson wrote:
> > I was actually wondering if a PC parallel port had enough speed to just
> > drive one of the Master-type Econet modules. Raw-speed-wise I think it
> > should have, but timing could be a problem due to the nature of the
> > polled-IO approach to driving a parallel port. Another back-burner
> > project I'd like to fiddle with sometime though...
> 
> Yeah, it'd be interesting to try.  Data throughput probably wouldn't be
> much of a problem, but again I suspect latency might be an issue.

Yep. If it really were that easy, why would Acorn invest time and money
in developing an entire ISA card? I believe PC parallel ports are still
hung up conforming to outdated ISA hardware, so even on a modern machine
there's a huge bottleneck in trying to drive a parallel port at high
speed.

Of course maybe a 'modern' ISA design with just a 68B54 and a few buffer
/ latch ICs thrown onto a prototyping board could do the job too. 

I'm not sure where the hang-up requiring Acorn to include a 6502 on the
ISA Econet board was - whether it was a speed issue with ISA bus itself
(and therefore still a problem with modern ISA bus systems which still
have to run at the original speed), or whether it was a speed issue with
the PC CPUs of the time (which wouldn't be a problem with modern
hardware)

> I guess it'd be easy enough to build a interface and try it out.  Maybe
> I'll have a go at that.

Let me know if you do. Building a system with Econet on one side and
Ethernet on the other could be useful. Now if only I could find a spec
document for RML's network protocol and build a PC board there too...

cheers

Jules