RE: [N8VEM-S100:273] Request For Comments (NIC Board)

["Andrew Lynch" <lyn...@yahoo.com>]

Hi Douglas!  Thanks!  You have to admit though, even 10 Mbps Ethernet on an
S-100 bus system would be something to see.  I do like the idea of moving
the TCP/IP stack to the NIC4 Z80 like using CP/NET or something akin to
that.  

Max is running CP/NET on the N8VEM home computer prototype so it is
certainly possible.  I am not sure how that would work though.  For most
applications, the 10 Mbps link would sufficient for most any S-100 based
application if not overkill.

Thanks and have a nice day!

Andrew Lynch

> -----Original Message-----
> From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On
> Behalf Of Douglas Goodall
> Sent: Thursday, June 09, 2011 2:54 AM
> To: n8vem...@googlegroups.com
> Subject: Re: [N8VEM-S100:273] Request For Comments (NIC Board)
> 
> Mike,
> 
> I looked over the specs for the ENC28J60 and I have some thoughts...
> 
> The chip is interfaced via SPI, which although fast is still a serial
> protocol.
> 
> The chip has on-board dual ported ram which is used for incoming and
> outgoing packets.
> 
> One of the things that slows down protocol stacks is the need to copy
> buffers around
> (something I learned in signal processing).
> 
> When a packet arrives, I assume it is placed in the dual ported ram of the
> ENC28J60,
> and can then be copied into the lower 4K at the bottom of the Z80's ram
> space. From
> there it would get copied yet again into the hosts systems space for
> further processing.
> 
> I can see several ways to make this all work better. For one thing I think
> adding four
> interfaces to the card is overkill. If the board could do a really good
> job with just one,
> that would be something.
> 
> You have to make a decision about how the board is to be used, and where
> the TCP/IP
> stack is going to live. Lets say you put this board into a Z/80 system in
> an S-100 bus,
> memory is short enough for the master CPU without having a full TCP stack
> there.
> 
> Doing a better job with just one channel might include making the master's
> window into
> the ram space of the on-board CPU the same size as the dual ported ram on
> the
> ENC28J60. Then the master would have access to the entire buffer space.
> The Z80
> on the board could manage the ENC28J60 and signal the master via IRQ or
> perhaps
> with a DMA terminal count condition.
> 
> Also the ENC28J60 is a 10base-T interface which I believe is limited to
> 10mb.
> 
> Just some thoughts...
> 
> Douglas
> 
> 
> On Jun 8, 2011, at 11:29 PM, mike wrote:
> 
> > -----BEGIN PGP SIGNED MESSAGE-----
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> >
> > Hi All,
> >
> > I just sketched out a design for a 4-port Ethernet S-100 card. I likely
> > won't get around to producing this for a while since I have enough on my
> > plate to keep me busy for quite some time, but it would be good to start
> > getting the ball rolling a little bit on something like this.
> >
> > http://www.8bit.geek/index.php/s100-cards-in-development/nic4-4-port-
> ethernet-card
> >
> > In a nutshell, it has an on-board Z/80 that bit-bangs an SPI bus
> > inter-connecting 4 ENC28J60 MAC/PHY ICs, and the Z80 has 32K of ram to
> > use as scratchpad and buffer space. The S100 master has access to a 4K
> > window at the bottom of the Z80s 32K RAM. There is one I/O port for
> > communicating comamnds and status between the S100 master and teh
> > on-board Z/80. The Z/80 can interrupt the bus master and interrupt
> > vector(s) are software programmable.
> >
> > Welcoming comments.
> >
> > - --Mike
> >
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