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Add ORB_QUEUE_LENGTH info

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Hamish Willee 2025-06-04 15:27:31 +10:00
parent 74570d5abe
commit 412e5169e9
1 changed files with 20 additions and 5 deletions
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docs/en/middleware/uorb.md
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@ -61,12 +61,12 @@ For example the [VelocityLimits](../msg_docs/VelocityLimits.md) message definiti
```text
# Velocity and yaw rate limits for a multicopter position slow mode only
uint64 timestamp # time since system start (microseconds)
uint64 timestamp # [us] Time since system start.
# absolute speeds, NAN means use default limit
float32 horizontal_velocity # [m/s]
float32 vertical_velocity # [m/s]
float32 yaw_rate # [rad/s]
float32 horizontal_velocity # [m/s] Horizontal velocity.
float32 vertical_velocity # [m/s] Vertical velocity.
float32 yaw_rate # [rad/s] Yaw rate.
```
By default this message definition will be compiled to a single topic with an id `velocity_limits`, a direct conversion from the CamelCase name to a snake_case version.
@ -92,15 +92,30 @@ To nest a message, simply include the nested message type in the parent message
```text
# Global position setpoint triplet in WGS84 coordinates.
#
# This are the three next waypoints (or just the next two or one).
uint64 timestamp # time since system start (microseconds)
uint64 timestamp # [us] Time since system start.
PositionSetpoint previous
PositionSetpoint current
PositionSetpoint next
```
### uORB Buffer Length
uORB messages have a single buffer by default, which may be overwritten if the message publication rate is too high.
Subscribers will then be able to read up to four messages in sequence before losing information, rather than just the last one sent.
You can create a message buffer using the named constant `ORB_QUEUE_LENGTH`.
The value is the length of the queue, which must be a power of 2 (so 2, 4, 8, ...).
For example, to create a four-message queue, add the following line to your message definition:
```sh
uint8 ORB_QUEUE_LENGTH = 4
```
### Message/Field Deprecation {#deprecation}
As there are external tools using uORB messages from log files, such as [Flight Review](https://github.com/PX4/flight_review), certain aspects need to be considered when updating existing messages: