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BLE: Add raw messages

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BLE can only fit 251 bytes of payload in notifications which isn't nearly enough for a raw V2X message.
So only publish a notification which message was received and let the client
poll the content from the characteristic (since reads can get data in fragments)
This commit is contained in:
Jannik Beyerstedt 2026-08-17 14:53:48 +02:00
commit 265f2e4eea
5 changed files with 411 additions and 82 deletions
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33
docs/ble-protocol.md
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@ -19,12 +19,16 @@ V2X data is exposed via the service UUID `c0b70000-d4f4-4000-ada8-f99a02ee315c`
UUID | Type | Description
------------------------------------- | --------------- | -----------
c0b70001-d4f4-4001-ada8-f99a02ee315c | `PositionState` | Set position from external source
c0b70001-d4f4-4002-ada8-f99a02ee315c | `RawMsgRx` | Raw CAM message (de-duplicated/ rate-limited)
c0b70001-d4f4-4003-ada8-f99a02ee315c | `CamEvent` | Latest received CAM
c0b70001-d4f4-4004-ada8-f99a02ee315c | `RawMsgRx` | Raw DENM message (de-duplicated/ rate-limited)
c0b70001-d4f4-4005-ada8-f99a02ee315c | `DenmEvent` | Latest received DENM
c0b70001-d4f4-4006-ada8-f99a02ee315c | `RawMsgRx` | Raw MAPEM message (de-duplicated/ rate-limited)
c0b70001-d4f4-4007-ada8-f99a02ee315c | `RawMsgRx` | Raw SPATEM message (de-duplicated/ rate-limited)
c0b70001-d4f4-4002-ada8-f99a02ee315c | `RawNotify` | Raw message notification
c0b70001-d4f4-4003-ada8-f99a02ee315c | `RawMsgRx` | Raw CAM message (de-duplicated/ rate-limited)
c0b70001-d4f4-4004-ada8-f99a02ee315c | `CamEvent` | Latest received CAM
c0b70001-d4f4-4005-ada8-f99a02ee315c | `RawMsgRx` | Raw DENM message (de-duplicated/ rate-limited)
c0b70001-d4f4-4006-ada8-f99a02ee315c | `DenmEvent` | Latest received DENM
c0b70001-d4f4-4007-ada8-f99a02ee315c | `RawMsgRx` | Raw MAPEM message (de-duplicated/ rate-limited)
c0b70001-d4f4-4008-ada8-f99a02ee315c | `RawMsgRx` | Raw SPATEM message (de-duplicated/ rate-limited)
Since a modern BLE notification can only fit up tp 251 bytes of payload, the raw messages can only be polled.
Please subscribe to `c0b70001-d4f4-4002-ada8-f99a02ee315c` and use the message ID to determine from which service to read the incoming value.
## Message Format
@ -101,3 +105,20 @@ 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)
Maximum message size (assuming realistic value ranges):
field name | tag size | (max.) data size
--------------------- | -------- | ---------
msg_type | 1 | 1 (VARINT(21))
payload | 1 | 2+1394 (LEN(1394) + payload)
**SUM** | 2 + | 1397 = 1399 byte
### Raw Message Notification
Maximum message size (assuming realistic value ranges):
field name | tag size | (max.) data size
--------------------- | -------- | ---------
msg_type | 1 | 1 (VARINT(21))
**SUM** | 1 + | 1 = 2 byte

4
docs/c_its-messages.proto
View file

@ -71,6 +71,10 @@ message RawMsgTx {
optional uint32 stationType = 6; // for source position vector
}
message RawNotify {
required uint32 message_type = 1; // ITS `MessageId` integer value
}
// ------------------------------
// Messages
// ------------------------------