Date   : Thu, 09 Aug 2007 23:08:45 +0100
From   : C.J.Thornley@... (Chris Thornley)
Subject: Emulating Econet hardware?

Hi,
That's great, I've been looking at the IC's Datasheet in the documentation
area of BBC Lives MC6854 (Page 6) This datagram seems to differ from ones
mentioned in the Econet AUG? 
The Flags and FCS/CRC are stripped but the packets within this don't seem to
compare to well to what I have seen written.

Perhaps there was an application note that was not published or something
from the manufactures explaining more about the chip?

Chris 


               />      Christopher J. Thornley is cjt@...
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 (*)OXOXOXOXO(*>=*=O=S=U=0=3=6=*=---------                             >
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               \>       Home Page :-http://www.coolrose.fsnet.co.uk
 
-----Original Message-----
From: bbc-micro-bounces+c.j.thornley=coolrose.fsnet.co.uk@...
[mailto:bbc-micro-bounces+c.j.thornley=coolrose.fsnet.co.uk@...
uk] On Behalf Of Jonathan Graham Harston
Sent: 09 August 2007 01:30
To: bbc-micro@...
Subject: Re: [BBC-Micro] Emulating Econet hardware?

Chris Thornley wrote:
> An Ethernet to econet device would require some sort of router (not 
> bridge) software to be written. Perhaps hiding the econet datagram's in IP
packets.
 
An Econet packet is encapsulated in an IP packet as follows:
 
Econet packet:
+------+------+-----+-----+---------+------+------------------------+
| Dest | Dest | Src | Src | Control |      |                        |
| Stn  | Net  | Stn | Net |  Byte   | Port |          Data          |
+------+------+-----+-----+---------+------+------------------------+
  <------ - - Packet Header - - ------>   <-- - Packet Data - -->
 
Becomes IP packet:
+-------------------+
| IP Header:        |
|  Version          |
|  Header Length    |
|  Type             |
|  Total Length     | <- header length + UDP packet length
|  ID               |
|  Fragment         |
|  Protocol         | <- UDP
|  Header CRC       |
|  Source Address   | <- source site.network.net.stn
|  Dest Address     | <- dest site.network.net.stn
|  Options          |
| ----------------- |
| IP Data:          |
|  UDP packet       |
|  +--------------+ |
|  | UDP Header:  | |
|  |  Source Port | |
|  |  Dest Port   | | <- &8000 for Econet-Over-IP
|  |  Length      | | <- Data length + UDP header length
|  |  Checksum    | |
|  | ------------ | |
|  | UDP Data:    | |
|  | +--------+   | |  Somewhere in here is:
|  | | Econet |   | |   Magic number &02
|  | | Packet |   | |   Port
|  | |  Data  |   | |   Control Byte
|  | +--------+   | |   Padding &00
|  +--------------+ |   Handle &nnnnnnnn
+-------------------+
 
(I'm sure I've posted this before...)
 
Conversely, an IP packet can be encapsulated in an Econet packet as
follows:
 
+------+------+-----+-----+---------+------+---------------+
| Dest | Dest | Src | Src | Control | Port | +-----------+ |
| Stn  | Net  | Stn | Net |  Byte   | &D2  | | IP Packet | |
|      |      |     |     |         |      | +-----------+ |
+------+------+-----+-----+---------+------+---------------+
The Flag byte determines the type of IP packet:
  &81 IP
  &A1 ARP_REQUEST
  &A2 ARP_REPLY
  &8F IPBCAST_REQUEST
  &8E IPBCAST_REPLY
 
> The first thing that need doing is for the econet protocol / 
> datagram's / command, will need to be documented, in an easy to follow 
> form. You should
 
It is documented, and I've been putting online at
http://mdfs.net/Comp/Econet
 
--
J.G.Harston - jgh@...                - mdfs.net/User/JGH BBC BASIC for 30+
platforms - http://mdfs.net/Software/BBCBasic

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