docs: Add BLE and UART protocol specification

Readme.md

@@ -1,4 +1,4 @@
-# ESP32-C5 C-ITS Visualizer
+# ESP32-C5 C-ITS Companion/ Visualizer
 
 Displays different C-ITS receive-only use cases for cheap.
 

docs/ble-protocol.md

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+# Bluetooth LE Protocol
+
+Some data is made available via BLE so that a smartphone app can be used to display it in other use cases.
+
+## General
+
+The BLE protocol contains some standardized services, but can also transport custom services.
+Each service is compromised of a set of characteristics which can be read or clients can even subscribe for changes.
+
+Sadly we can't use any of the standardized service/ profiles to transmit V2X data.
+Even notifications about DENMs can't be transmitted since the Alert Notification Profile is only meant for the companion device to query notifications from the phone, but not the other way around.
+
+So we will only use the Device Information Service to announce ourselves and use a custom service for everything else.
+
+## V2X BLE Service
+
+V2X data is exposed via the service UUID `c0b70000-d4f4-4000-ada8-f99a02ee315c` (randomly generated UUID, with byte 3 and 4 set to zero) using the following characteristics:
+
+UUID                                  | Type            | Description
+------------------------------------- | --------------- | -----------
+c0b70001-d4f4-4001-ada8-f99a02ee315c  | `PositionState` | Set position from external source
+c0b70001-d4f4-4001-ada8-f99a02ee315c  | `RawMsgRx`      | Raw CAM message (de-duplicated/ rate-limited)
+c0b70001-d4f4-4002-ada8-f99a02ee315c  | `CamEvent`      | Latest received CAM
+c0b70001-d4f4-4003-ada8-f99a02ee315c  | `RawMsgRx`      | Raw DENM message (de-duplicated/ rate-limited)
+c0b70001-d4f4-4004-ada8-f99a02ee315c  | `DenmEvent`     | Latest received DENM
+c0b70001-d4f4-4005-ada8-f99a02ee315c  | `RawMsgRx`      | Raw MAPEM message (de-duplicated/ rate-limited)
+c0b70001-d4f4-4006-ada8-f99a02ee315c  | `RawMsgRx`      | Raw SPATEM message (de-duplicated/ rate-limited)
+
+## Message Format
+
+Messages are encoded according to the [Protocol Buffers](https://protobuf.dev/) specification since it provides decent binary size and has parser libraries for many programming languages.
+All data types are defined in one `.proto` file: [c_its-messages.proto](./c_its-messages.proto).
+
+### Position State Input
+
+When there's no GNSS receiver connected to the ESP, position, heading and speed information can be set using a `PositionState` message (see [c_its-messages.proto](./c_its-messages.proto)).
+
+### DENM Event
+
+Each received DENM will be "published" as a `DenmEvent` message (see [c_its-messages.proto](./c_its-messages.proto)).
+Repetitions of the same message (e.g. no changes to the validity timeframe and location) may be dropped by the BLE server.
+
+### CAM Event
+
+Each received (low-frequency) CAM will be "published" as a `CamEvent` message (see [c_its-messages.proto](./c_its-messages.proto)).
+
+### Raw Received Message
+
+Received V2X messages will be "published" as a `RawMsgRx` message (see [c_its-messages.proto](./c_its-messages.proto)).
+Repetitions of the same message should be dropped by the BLE server.
+Consecutive messages with no relevant changes may be dropped by the BLE server while keeping some minimal publishing rate, e.g.:
+- only publish MAPEMs every 10 seconds (since content doesn't change, but client may be restarted after first MAPEM from an intersection was received)
+- drop high-frequency CAMs (only publish "full" CAMs which include the low-frequency container)

docs/c_its-messages.proto

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+syntax = "proto2";
+
+package c_its_io;
+
+// ------------------------------
+// Data Types
+// ------------------------------
+
+message Position {
+  required  float     latitude_deg              =  1;
+  required  float     longitude_deg             =  2;
+}
+
+enum TrafficDir {
+  // for all directions of traffic
+  ALL_DIRECTIONS                                =  0;
+  // for the direction of traffic according to the reference direction, and the portion of traffic upstream of the reference position
+  UPSTREAM                                      =  1;
+  // for the direction of traffic according to the reference direction, and the portion of traffic downstream of the reference position
+  DOWNSTREAM                                    =  2;
+  // for the direction of traffic opposite to the reference direction
+  OPPOSITE                                      =  3;
+}
+
+message VehicleContainer {
+  optional  uint32        heading_deg           =  1; // vehicle heading in degrees, if not "unavailable"
+  optional  uint32        speed                 =  2; // vehicle speed in 1/100 m/s, if not "unavailable"
+  optional  uint32        vehicle_length_dm     =  3; // vehicle length in 1/10 m, if not "unavailable"
+  optional  uint32        vehicle_width_dm      =  4; // vehicle width in 1/10 m, if not "unavailable"
+}
+
+
+// GeoNetworking Destination Area Shape
+enum GNAreaShape {
+  ETSI_AREASHAPE_CIRCLE                         =  0;
+  ETSI_AREASHAPE_RECTANGLE                      =  1;
+  ETSI_AREASHAPE_ELLIPSIS                       =  2;
+  ETSI_AREASHAPE_UNKNOWN                        = 15;
+}
+
+// GeoNetworking Destination Area/ Source Position
+message ITSPosition {
+  optional  int32         latitude              =  1; // Latitude in 1/10th of micro degrees
+  optional  int32         longitude             =  2; // Longitude in 1/10th of micro degrees
+}
+
+// GeoNetworking Destination Area
+message GNArea {
+  optional  GNAreaShape   area                  =  1 [default = ETSI_AREASHAPE_UNKNOWN];
+  optional  ITSPosition   position              =  2;
+  optional  int32         distA                 =  3; // Distance A of the geometric shape in meters
+  optional  int32         distB                 =  4; // Distance B of the geometric shape in meters, mandatory for rectangle and ellipsis
+  optional  int32         angle                 =  5; // Angle of the geometric shape in degrees, mandatory for rectangle and ellipsis
+}
+
+// GeoNetworking Transport
+enum GNTransport {
+  GN_TRANSPORT_DEFAULT                          =  0;
+  GN_TRANSPORT_GUC                              =  2; // GeoUnicast
+  GN_TRANSPORT_GAC                              =  3; // Geographically-Scoped Anycast
+  GN_TRANSPORT_GBC                              =  4; // Geographically-Scoped broadcast
+  GN_TRANSPORT_TSB                              =  5; // Topologically-scoped broadcast
+  GN_TRANSPORT_SHB                              =  7; // Single hop broadcast
+}
+
+message RawMsgTx {
+  required bytes          payload               =  1; // as UPER
+  required uint32         message_type          =  2; // ITS `MessageId` integer value
+
+  required GNTransport    gnTransport           =  3;
+  required GNArea         gnArea                =  4;
+  required uint32         hopLimit              =  5;
+}
+
+// ------------------------------
+// Messages
+// ------------------------------
+
+message PositionState {
+  required  Position      position              =  1;
+  optional  uint32        heading_deg           =  2;
+  optional  uint32        speed                 =  3; // speed in 1/100 m/s
+}
+
+message DenmEvent {
+  required  fixed64       timestamp             =  1; // DENM reference time as UNIX time
+  required  fixed64       validity_end_ts       =  2; // UNIX time when event validity ends (from denm.management.validityDuration)
+  required  fixed32       station_id            =  3; // unique ID of the event when combined with `seq_num`
+  required  uint32        seq_num               =  4; // unique ID of the event when combined with `station_id`
+  optional  Position      event_position        =  5; // event location (from denm.management.eventPosition)
+  optional  uint32        event_heading_deg     =  6; // event heading (from denm.location.eventPositionHeading)
+  optional  TrafficDir    direction             =  7; // relevance traffic direction (from denm.management.trafficDirection)
+  optional  uint32        cause_code            =  8;
+  optional  uint32        sub_cause_code        =  9;
+}
+
+message CamEvent {
+  required  fixed32       station_id            =  1; // Station ID of the vehicle
+  required  uint32        station_type          =  2; // ITS `StationType`
+  required  Position      position              =  3; // vehicle position
+  optional  uint32        vehicle_role          =  4; // ITS `VehicleRole`
+  optional  VehicleContainer  vehicle_data      =  5; // speed, etc unless CAM contains an RSU container
+}
+
+message RawMsgRx {
+  required  uint32        msg_type              =  1; // ITS message type (`MessageId` from PDU header)
+  required  bytes         payload               =  2; // UPER message with Geonetworking and BTP headers
+}
+
+message SerialOutputMsg {
+  oneof                   payload {
+    DenmEvent             denm                  =  1;
+    RawMsgRx              rx_msg                =  2;
+  }
+}
+
+message SerialInputMsg {
+  oneof                   payload {
+    PositionState         position              =  1;
+    RawMsgTx              tx_msg                =  2;
+  }
+}

docs/uart-protocol.md

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+# UART Protocol
+
+If enabled using the `TODO` feature flag, all received messages are transmitted on UART using the protocol described in this document.
+The serial communication can also be used to send V2X data.
+
+## Message Format
+
+The UART communication is using a custom framing protocol to encapsulate binary messages.
+The payload is:
+
+- a `SerialOutputMsg` for transmissions from the ESP to the host or
+- a `SerialInputMsg` for transmissions from the host to the ESP
+
+in binary [Proto](https://protobuf.dev/) serialization according to the [c_its-messages.proto](./c_its-messages.proto) definition.
+
+Each transmission:
+- starts with a Start of Frame (SOF) sequence: `0x56, 0x32, 0x58, 0x2B` ("V2X+")
+- followed by a 16-bit big-endian length field
+- followed by the payload
+- followed by an End of Frame (EOF) sequence `0x0d, 0x0a`