# uORB 消息

# 简介

uORB 是一种异步 publish()/subscribe() 的消息传递 API,用于进程或者线程间通信(IPC)。

查看 教程 以了解如何在 C++ 中使用它。

作为很多应用程序依赖的uORB,会在启动时自动启动。 它以 uorb start</0 > 开头。 单元测试可以从 <code>uorb_tests 开始。

# 添加新 Topic(主题)

新的uORB</0>主题通过在主要的PX4/Firmware 存储库中添加,也能通过在out-of-tree</0>消息定义中添加。 有关添加树外 uORB 消息定义的信息,请参阅 本节

若要添加新主题,需要在 msg/ 目录中创建一个新的 .msg 文件,并将文件名添加到 msg/CMakeLists.txt 列表中。 由此,将自动生成所需的 C/C++ 代码。

查看支持类型的现有 msg 文件。 消息还可以在其他消息中嵌套使用。

对于每个生成的 C/C + 结构,将添加一个字段 uint64_t timestamp。 此用于记录日志,因此请确保在发布时填充数据。

若要在代码中使用该主题,请包括头文件:

#include <uORB/topics/topic_name.h>

通过在 .msg 文件中添加如下内容的行,可以将一条消息定义用于多个独立主题:

# TOPICS mission offboard_mission onboard_mission

然后在代码中,将它们用作主题 id: ORB_ID(offboard_mission)

# 发布

发布主题可以在系统中的任何位置完成,包括中断上下文(由 hrt_call API 调用的函数)。 但是,仅在中断上下文之外才能为主题做广播。 一个主题必须与以后发布的过程相同。

# 主题列表和监听(Listener)

要列出所有主题,列出文件句柄:

要监听五条信息中的一个主题内容,运行监听器:

ls /obj

输出主题内容如下:

listener sensor_accel 5

uorb top 命令实时显示每个主题的发布频率。

TOPIC: sensor_accel #3
timestamp: 84978861
integral_dt: 4044
error_count: 0
x: -1
y: 2
z: 100
x_integral: -0
y_integral: 0
z_integral: 0
temperature: 46
range_m_s2: 78
scaling: 0

TOPIC: sensor_accel #4
timestamp: 85010833
integral_dt: 3980
error_count: 0
x: -1
y: 2
z: 100
x_integral: -0
y_integral: 0
z_integral: 0
temperature: 46
range_m_s2: 78
scaling: 0

提示

On NuttX-based systems (Pixhawk, Pixracer, etc) the listener command can be called from within the QGroundControl MAVLink Console to inspect the values of sensors and other topics. This is a powerful debugging tool because it can be used even when QGC is connected over a wireless link (e.g. when the vehicle is flying). For more information see: Sensor/Topic Debugging.

# uorb top 命令

The command uorb top shows the publishing frequency of each topic in real-time:

update: 1s, num topics: 77
TOPIC NAME                        INST #SUB #MSG #LOST #QSIZE
actuator_armed                       0    6    4     0 1
actuator_controls_0                  0    7  242  1044 1
battery_status                       0    6  500  2694 1
commander_state                      0    1   98    89 1
control_state                        0    4  242   433 1
ekf2_innovations                     0    1  242   223 1
ekf2_timestamps                      0    1  242    23 1
estimator_status                     0    3  242   488 1
mc_att_ctrl_status                   0    0  242     0 1
sensor_accel                         0    1  242     0 1
sensor_accel                         1    1  249    43 1
sensor_baro                          0    1   42     0 1
sensor_combined                      0    6  242   636 1

请确保不要为同一主题混合 orb_advertise_multiorb_advertise

# 多实例

uORB provides a mechanism to publish multiple independent instances of the same topic through orb_advertise_multi. It will return an instance index to the publisher. A subscriber will then have to choose to which instance to subscribe to using orb_subscribe_multi (orb_subscribe subscribes to the first instance). Having multiple instances is useful for example if the system has several sensors of the same type.

下面解释了一些常见的陷阱和边界案例:

The full API is documented in platforms/common/uORB/uORBManager.hpp (opens new window).

# 故障排除和常见的陷阱

As there are external tools using uORB messages from log files, such as Flight Review (opens new window), certain aspects need to be considered when updating existing messages:

  • Changing existing fields or messages that external tools rely on is generally acceptable if there are good reasons for the update. In particular for breaking changes to Flight Review, Flight Review must be updated before code is merged to master.
  • In order for external tools to reliably distinguish between two message versions, the following steps must be followed:
    • Removed or renamed messages must be added to the deprecated_msgs list in msg/CMakeLists.txt (opens new window) and the .msg file needs to be deleted.
    • Removed or renamed fields must be commented and marked as deprecated. For example uint8 quat_reset_counter would become # DEPRECATED: uint8 quat_reset_counter. This is to ensure that removed fields (or messages) are not re-added in future.
    • In case of a semantic change (e.g. the unit changes from degrees to radians), the field must be renamed as well and the previous one marked as deprecated as above.