Brontekst bekijken van Its-g5

{{Project
   |Name=ITS-G5
   |Picture=its-g5.png
   |Omschrijving=Investigating ITS-G5 signals
   |Status=In progress
   |Contact=bertrik
  }}

== Introduction ==
[[File:its-g5-wireshark.png|thumb|right|alt=wireshark analysis]]

This page is about investigating reception and processing of so-called C-ITS or ITS-G5 signals (802.11p) as used in the Netherlands, see also https://en.wikipedia.org/wiki/Vehicle-to-everything
These signals are exchanged between passenger cars, emergency vehicles, traffic lights and other traffic-related equipment.

An ESP32-C5 development board is capable of receiving WiFi in the 5 GHz band and can receive/sniff these kinds of packets from live traffic.

Stuff to investigate:
* Source code for an ITS-G5 receiver https://github.com/pit711/v2x2map
* Crowd-sourced live map of messages received: https://opentrafficmap.org/
* Simplest source code for Arduino-based sniffer: https://git.devlol.org/jstsmthrgk/simple-its-g5-receiver-firmware
* How to contribute to opentrafficmap: https://wiki.opentrafficmap.org

In the Netherlands, SPAT/MAPem messages from traffic lights are not transferred over wifi-p, but over UDAP.
You need credentials to access that data, it is not clear if it is feasible to hobbyist to access it.
Interesting project: https://github.com/idkmanLool9/Verkeerslicht

== Design ==
[[File:esp32-c5-sniffer.jpg|thumb|right|alt=esp32-c5-sniffer]]

The design is:
* Use an esp32-c5 for sniffing 802.11p frames only
* Use an esp32-c3 (as an inexpensive jellybean part) for receiving sniffed frames from the esp32-c5, connect to WiFi and upload packets over MQTT
* The interface beteween the two boards is '''serial''', this is simpler than SPI as used in other projects:
** Only three wires required: GND, +5V and serial DATA
** No need to desolder capacitors on SPI wires of the esp32-c5
** A serial interface is more universal, e.g. can be connected to an arbitrary linux SBC, to run a python bridge for example
** On the esp32-c5 use the same wires as the existing USB-UART bridge, so you can also receive packets over USB-serial
* Run a simple web server on the esp-c3:
** Configuration page with MQTT settings: host, port, user, pass, base topic
** Perhaps configure a keystore/certificate for secure mqtt (mqtts), if needed
** Optional: show some nice stats: mqtt status, packet rate, last packet, packets per type
** Optional: run a very basic parser for e.g. CAM messages

Practical:
* The serial link runs over the USB-UART chip of the esp32-c5.
* A simple command processor runs on the other UART (the emulated USB serial port)
* On the esp32-c5 side, use pins GND, 5V, UART-TX for the ESP-ESP serial connection.
* The esp32-c3 and esp32-c5 share their 5V and GND power lines. Each board derives its own internal power supplies from this 5V.
* The serial link doesn't have to be very high speed, 115200 for example. We use a hardware UART on both sides of the serial link.
* Use https://registry.platformio.org/libraries/thomasfredericks/MicroSlip for framing packets over the serial port.

== Hardware ==
[[File:esp32-c5-devkitc-1.jpg|thumb|right|alt=esp32-c5]]
[[File:esp32-c3-supermini.jpg|thumb|right|alt=esp32-c3]]

I got an ESP32-C5-devkitC-1 board, and it worked for me:
* Aliexpress product page https://nl.aliexpress.com/item/1005012416463528.html
* Espressif schematic https://dl.espressif.com/dl/schematics/SCH_ESP32-C5-DevkitC-1_V1.1_20240621.pdf . Actually my board is not exactly like this, the USB-UART is connected to pins GPIO11 (TX) and GPIO12 (RX), not GPIO25/GPIO24.
* Espressif devkit-c page: https://docs.espressif.com/projects/esp-dev-kits/en/latest/esp32c5/esp32-c5-devkitc-1/user_guide.html

It has an onboard antenna. There are also other boards with an antenna connection, which allows using an external antenna. This may be better, I don't know yet.

How to wire it up, what I did:
* Put both the esp32-c3-supermini board and the esp32-c5-devkit-c1 on a breadboard
* Use male-male dupont wires to connect:
** 5V to 5V, GND to GND, esp32-c5 TX to esp32-c3 RX
* Programmed the esp32-c5 with firmware
* Plug an USB-C cable into the esp32-c3, programmed it with firmware, now it's powering both the esp32-c3 and the esp32-c5

{| class="wikitable" style="margin:auto"
|+ Connections
|-
! ESP32-c5 !! ESP32-c3 !! Remark
|-
| GND || GND || shared ground
|-
| 5V || 5V || raw power
|-
| U0TXD/GPIO11 || RX/GPIO20 || Data link
|}

== Software ==
See https://github.com/bertrik/its-g5-receiver

This is heavily inspired by https://git.devlol.org/jstsmthrgk/simple-its-g5-receiver-firmware
but with a fixed size ring buffer instead of dynamic allocation.

=== Compiling the firmware ===
Uses python and platformio, see the README.md in the source archive.

Watch packets come in:
  pio device monitor
Packets are logged as a 'hexdump'.

The can be converted for wireshark, for example:
  text2pcap -l 105 message.txt message.pcap
Then viewed in wireshark:
  wireshark message.pcap

=== opentraffic map interface ===
See https://github.com/MPW1412/openwrt-otm-bridge#wire-format-mimics-the-esp32-c5-firmware for the mqtt wire format.

See also https://github.com/pit711/v2x2map/blob/main/firmware/main/mqtt.c

In short: server = mqtts://cits1.opentrafficmap.org:8883 :
* no user name / password
* topic 'its/<node>/status' (online or offline), retained
* topic 'its/<node>/info' with a JSON string, like {"emac":"xx:xx:xx:xx:xx:xx","ver":"github.com/bertrik/its-g5-receiver-v0.0.1","hwv":"esp32-c5-devkit-c1"}
* topic 'its/<node>/packet' for sniffed packets (raw, not JSON encoded)