The eeBridge project
designing a bridge between an Econet and an Ethernet network


1. Introduction

For some time now i've been thinking of hooking an Acorn Econet to my Ethernet LAN. The reason for this is that I have several Acorn BBC machines and the software for these machines is stored on 5 ¼ inch floppydisks. Some of these were formatted in 1982, so you can guess that after 20 years of use and lying around in storage boxes not all data is error-free readable. Also, the 5 ¼ inch floppy drives become rapidly extinct, and the ones lying around can get more and more hardware errors over the years.

Because of this, I've been thinking of using an PC clone as an econet fileserver. But then again, while I'm at the job I might as well design an Econet-Ethernet bridge. It shouldn't be that difficult, all it takes is an microprocessor or -controller, an Econet interface, an Ethernet interface and some RAM and EEPROM. And thus the eeBridge project was born.


2. Goals

Hardware:


    * Enough on-board RAM and FlashROM for future expansions
    * Onboard serial interface
    * Onboard clock circuitry based upon second generation clock boxes(http://www.beebmaster.co.uk/EconetClocks.html#Acorn2)/SJResearch clock boxes(http://www.beebmaster.co.uk/EconetClocks.html#SJ) (allow to set the duty cycle), which preferably can be switched on and off using software
    * Signal LED's for Ethernet data, Ethernet link, Econet data and Econet link on frontpanel
    * Master Econet 6-chip module instead of the 4-chip module. 6-chip modules contain collision detection
    * Optional: Real-time clock?
    * Optional: Built-in IDE-controller?


Software:


    * Transparent Econet-Ethernet file access (using FTP or Samba)
    * Econet protocol over IP support
    * Serial and telnet access for configuration and firmware upgrades
    * Optional: Web-based configuration
    * Optional: Built-in Level2/3 Econet fileserver?




3. Rough design

For the ethernet controller there are basically two chips which are suitable for this project, the Cirrus Logic CS8900(http://www.cirrus.com/en/products/pro/detail/P46.html) and the Realtek RTL8019 controllers(http://www.realtek.com.tw/products/products1-2.aspx?modelid=1). I made a loose sketch for a first rough design(http://capone.xs4all.nl/moduledata/filebrowser/projects/eeBridge/eeBridge.jpg) based on a Motorola 68HC11 or 68HC12 microcontroller, a standard Acorn Master Econet module(http://capone.xs4all.nl/moduledata/filebrowser/projects/eeBridge/BBC-Econet.jpg) and a readily available CS8900 module(http://www.embeddedether.net/). By using these modules the design and manufacturing will be easier and the costs will probably be lower.
I've added the possibility to add hardware for an IDE interface. Maybe this will come in handy in the future if I decide to program some sort of Econet fileserver functionality in the eeBridge

Update 2013-11-26:
Component list:
* Raspberry Pi version B (includes ethernet port)
* Slice-of-PI/O (interface between Raspberry Pi and Econet Module)
* Econet module


4. ....