Update README.md

README.md

@@ -17,11 +17,13 @@ Locapack is distributed under the GPLv3 license. Please refer to the `LICENSE` f
 
 ### Packet general structure
 
-|    2B    |         2B        |    1B (opt)   |  variable   |      1B       |            variable           |
-|:--------:|:-----------------:|:-------------:|:-----------:|:-------------:|:-----------------------------:|
-| `header` | `sequence_number` | `movement_id` | `device_id` | `payload_len` | `localisation_packet_payload` |
+|    2B    |    0/5B     |         2B        |    1B (opt)   |  variable   |      1B       |            variable           |
+|:--------:|:-----------:|:-----------------:|:-------------:|:-----------:|:-------------:|:-----------------------------:|
+| `header` | `timestamp` | `sequence_number` | `movement_id` | `device_id` | `payload_len` | `localisation_packet_payload` |
 
-The `sequence_number` field is mandatory. 
+The `sequence_number` field is mandatory.
+
+The `timestamp` field is optional and its presence is announced in the header. The timestamp field contains the number of milliseconds since the boot of the local system. 
 
 The `movement_id` field is optional and its presence is announced in the header.
 
@@ -34,9 +36,9 @@ The `localisation_packet_payload` length depends on the `localisation_packet_typ
 
 ### Header structure
 
-|         4b         |        4b        |            4b              |             1b              |    3b    |
-|--------------------|------------------|----------------------------|-----------------------------|----------|
-| `protocol_version` | `device_id_size` | `localisation_packet_type` | `movement_id_presence_flag` | reserved |
+|         4b         |        4b        |            4b              |             1b              |           1b              |    2b    |
+|--------------------|------------------|----------------------------|-----------------------------|---------------------------|----------|
+| `protocol_version` | `device_id_size` | `localisation_packet_type` | `movement_id_presence_flag` | `timestamp_presence_flag` | reserved |
 
 The `protocol_version` field indicates the version of the localisation packet used. This documentation describes the version #1 of the localisation packet protocol.
 
@@ -50,6 +52,8 @@ The `localisation_packet_type` indicates the structure of the payload. These typ
 
 The `movement_id_presence_flag` must be set to 1 if the `movement_id` field is present in the packet.
 
+The `timestamp_presence_flag` must be set to 1 if the `timestamp` field is present in the packet.
+
 ### Payload structure by packet type
 
 #### Type 0 : Universal GNSS localisation