N-Break — Econet-over-WiFi (AUN) Gateway

Overview

N-Break is an Econet-over-WiFi interface that allows a retro BBC Micro to communicate with an AUN fileserver (or other device) over a modern IP network.

It recreates the classic Econet experience using inexpensive, readily available hardware - no custom PCBs or extensive soldering required.

Thanks

A number of folks over at https://stardot.org.uk/ have helped with the testing this software; as well as providing insights into the inner workings of these protocols, without which the development would have taken much longer. Special mentions to @IanJeffray and @radiofan for enthusiastically jumping in and building and testing their own versions of the hardware.

Hardware Requirements

To build the interface, you will need:

• 1 × ESP32-C6 module Example: https://it.aliexpress.com/item/1005007399157637.html Approx. price: €5.39

• 2 × RS422/RS485 transceiver modules Example: https://it.aliexpress.com/item/32688467460.html Approx. price: €1.69 each

• 1 × 5-pin DIN plug and twisted-pair cable (e.g., CAT5)

• Jumper/Dupont wires to connect everything

• 3 resistors for Econet termination and biasing:

  • 1 × 110 Ω termination
  • 2 × 550 Ω idle bias

Hardware Assembly

Connect the components as shown in the schematic:

*-Schematic note: The clock pins in a previous version of this schematic were reversed, as stated in The Econet System User Guide however this was not correct and later documentation shows them reversed.

Note: Power the RS485 driver modules from 3.3 V.

Final assembly complete with Econet plug ready for use:

Upload the firmware to your ESP32

Connect your ESP32 via USB (left socket) and identify the serial port your computer assigned it.

Download the release zip you want to install from the releases on this page.

esptool running in Python 3 is used to upload the firmware. Adjust these steps for your envrionment as nescessary.

# Create an empty directory for hosting esptool
mkdir nbreak-tmp
cd nbreak-tmp

# Create virtual environment and install esptool inside of it
python -mvenv venv --prompt nbreak-flash
source venv/bin/activate
pip install esptool

# Unzip the firmware release bundle
unzip /path/to/nbreak-firmware-xxx.zip
cd dist/

# Flash it - NOTE: CHANGE /dev/ttyXXX to the serial port your ESP32 is on!
python -m esptool --port /dev/ttyXXX --chip esp32c6 -b 460800 --before default_reset --after hard_reset write_flash "@flash_args"

# Clean up
deactivate
cd ../../
rm -rf nbreak-tmp

Device Configuration and monitoring

After flashing, the device will start a Wi-Fi access point named nbreak-econet.

1. Connect to the access point.

2. Open a browser and go to http://192.168.4.1. You can select the menu items on the left.

3. After connecting WiFi and verifying you have access, you can configure the Econet/AUN settings.

The example screenshot below is for a BBC Micro whose station ID is 127 and a fileserver at 192.168.0.1.

The first table, the Econet Stations list, should specify the station numbers on your Econet that you intend to expose to the IP network. N-Break will monitor the designated port for traffic addressed to these stations. Currently you can have a maximum of 5. Additional entries will not be loaded.

The second table defines the AUN IP hosts that you want to present to the Econet network. N-Break will listen on the Econet for these station IDs and respond on their behalf, forwarding the traffic to the specified IP address and port.

For communications to be successful, you need at least one entry in both tables.

AUN Fileserver Setup

A couple of AUN Fileservers have been tested. The best so far is the one included with PiEconetBridge. Despite the name, you can run the fileserver easily without needing either a Raspberry Pi or the Econet bridge hardware and it's very good.

An honorable mention goes to aund. This was what I developed the original code against. It was what first sent the Pacman2 binary to my real-life BBC over Econet bringing it to life with lights and sound. Alas it has some bugs which made me look for alternatives.

Example configuration files for both are included in the contrib/ directory under peb and aund respectively.

Uplinks

N-Break now supports uplinks (trunks) to wide-area Econet networks using the Bridge-over-IP protocol developed by the PiEconetBridge team.

To configure an uplink via PiEconetBridge, add a TRUNK line to your configuration:

TRUNK ON PORT 32769 TO DYNAMIC KEY thisIsThe32ByteKey

Enter the same port and key details in the Uplinks tab of the PiEconetBridge web interface.

Once the connection is established, remote Econet networks hosted by PiEconetBridge will appear on your local Econet as additional networks.

Building the firmware yourself

Firmware is built and flashed using idf.py from version 5.5.1 of the ESP-IDF toolchain.

Please note the ESP-IDF version number specified above. It is required because in order to reduce latency, we access internal private data of the PARLIO driver to give us better control of the DMA scheduling, FIFO loading and start/stop control of the peripheral.

1. Install ESP-IDF: https://docs.espressif.com/projects/esp-idf/en/stable/esp32/get-started/index.html

2. Install PNPM and NodeJS - this is used to build the web front end. https://pnpm.io/installation

   Adapt these steps for your environment:

   curl -fsSL https://get.pnpm.io/install.sh | bash -
   source ~/.bashrc
   pnpm env use -g 22

3. Build and flash the firmware:

   idf.py flash

Enjoy!