本文主要内容翻译自官方文档:https://dev.px4.io/en/middleware/uorb.html
在前一篇笔记中使用uORB完成消息传递,实现了一个简单示例程序,本文将对uORB进行系统学习。
uORB是一种异步发布(publish)/订阅(subscribe)机制的消息API,该机制用于在线程/进程之间通信。uORB在其他程序启动之前自动启动,因为其他很多程序依赖于他。
使用uorb start命令启动它,可以使用uorb_tests开始单元测试。
- 加入一个新主题
可以在msg/文件夹里新建一个.msg文件来创建一个新主题,并在msg/CMakeLists.txt中加入,则在编译时会自动生成对应的C/C++代码。
例如下面是vehicle_attitude.msg中的内容:
# This is similar to the mavlink message ATTITUDE_QUATERNION, but for onboard use
float32 rollspeed # Angular velocity about body north axis (x) in rad/s
float32 pitchspeed # Angular velocity about body east axis (y) in rad/s
float32 yawspeed # Angular velocity about body down axis (z) in rad/s
float32[4] q # Quaternion (NED)
# TOPICS vehicle_attitude vehicle_attitude_groundtruth vehicle_vision_attitude
在编译后,将在编译目录的src/modules/uORB/topics文件夹下生成vehicle_attitude.h头文件,内容如下:
/****************************************************************************
*
* Copyright (C) 2013-2016 PX4 Development Team. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name PX4 nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/* Auto-generated by genmsg_cpp from file /home/spy/src/Firmware/msg/vehicle_attitude.msg */
#pragma once
#include <stdint.h>
#ifdef __cplusplus
#include <cstring>
#else
#include <string.h>
#endif
#include <uORB/uORB.h>
#ifndef __cplusplus
#endif
#ifdef __cplusplus
struct __EXPORT vehicle_attitude_s {
#else
struct vehicle_attitude_s {
#endif
uint64_t timestamp; // required for logger
float roll;
float pitch;
float yaw;
float q[4];
uint8_t _padding0[4]; // required for logger
#ifdef __cplusplus
#endif
};
/* register this as object request broker structure */
ORB_DECLARE(vehicle_attitude);
ORB_DECLARE(vehicle_attitude_groundtruth);
ORB_DECLARE(vehicle_vision_attitude);
对于生成的每个C/C++结构体,将会自动添加一个uint64_t timestamp成员,该成员用于logger模块记录数据,所以确保在发布消息时给该成员赋值。
为了在代码里使用该主题,需要包含如下头文件:
#include <uORB/topics/topic_name.h>
在.msg的代码中加入如下行,则一条msg定义可以被多个独立的主题实例所使用:
# TOPICS mission offboard_mission onboard_mission
之后可以在代码中使用 ORB_ID(offboard_mission)来获取主题ID。
- 发布主题
可以在系统中的任何位置发布主题,包括中断内容中(hrt_call API调用的函数)。但是,只能在中断内容之外广播主题。必须同一进程中广播主题,以便随后发布他(不太理解这句话的意思)。
- 列出和监听主题
要列出所有的主题,使用
笔者在飞控刚开机时使用qgroundcontrol的MAVLink控制台,得到所有主题列表如下图:
nsh> ls /obj
/obj:
_obj_
actuator_armed0
actuator_controls_00
actuator_controls_10
actuator_controls_20
actuator_controls_30
actuator_outputs0
actuator_outputs1
adc_report0
airspeed0
att_pos_mocap0
battery_status0
camera_capture0
camera_trigger0
commander_state0
control_state0
cpuload0
differential_pressure0
distance_sensor0
ekf2_innovations0
ekf2_timestamps0
esc_status0
estimator_status0
fw_pos_ctrl_status0
geofence_result0
gps_dump0
gps_inject_data0
home_position0
input_rc0
led_control0
log_message0
manual_control_setpoint0
mavlink_log0
mc_att_ctrl_status0
mission_result0
multirotor_motor_limits0
multirotor_motor_limits1
offboard_control_mode0
offboard_mission0
onboard_mission0
optical_flow0
parameter_update0
position_setpoint_triplet0
power_button_state0
rc_channels0
rc_parameter_map0
safety0
satellite_info0
sensor_accel0
sensor_accel1
sensor_accel2
sensor_baro0
sensor_baro1
sensor_combined0
sensor_correction0
sensor_gyro0
sensor_gyro1
sensor_gyro2
sensor_mag0
sensor_mag1
sensor_mag2
sensor_mag3
sensor_preflight0
sensor_selection0
servorail_status0
subsystem_info0
system_power0
task_stack_info0
tecs_status0
telemetry_status0
uavcan_parameter_request0
uavcan_parameter_value0
vehicle_attitude0
vehicle_attitude_setpoint0
vehicle_command0
vehicle_command_ack0
vehicle_control_mode0
vehicle_global_position0
vehicle_gps_position0
vehicle_land_detected0
vehicle_local_position0
vehicle_local_position_setpoint0
vehicle_rates_setpoint0
vehicle_status0
vehicle_status_flags0
vehicle_vision_attitude0
vehicle_vision_position0
vtol_vehicle_status0
wind_estimate0
使用 listener 可以监听主题:
文档中给出listener只能在Pixracer中使用,不过笔者使用pixhawk2.1运行pixhawk固件,也可以运行listener命令
结果如下:
nsh> listener sensor_accel 5
TOPIC: sensor_accel instance 0 #1
timestamp: 45504766
integral_dt: 4000
error_count: 0
x: 0.0126
y: 0.4502
z: -9.7865
x_integral: 0.0001
y_integral: 0.0018
z_integral: -0.0392
temperature: 44.7562
range_m_s2: 156.9064
scaling: 0.0048
x_raw: 41
y_raw: -123
z_raw: -2067
temperature_raw: 3522
device_id: 1442082
TOPIC: sensor_accel instance 0 #2
timestamp: 45564766
integral_dt: 3991
error_count: 0
x: 0.0208
y: 0.4487
z: -9.7956
x_integral: 0.0001
y_integral: 0.0018
z_integral: -0.0390
temperature: 44.7424
range_m_s2: 156.9064
scaling: 0.0048
x_raw: 45
y_raw: -121
z_raw: -2067
temperature_raw: 3517
device_id: 1442082
TOPIC: sensor_accel instance 0 #3
timestamp: 45620766
integral_dt: 4000
error_count: 0
x: 0.0133
y: 0.4447
z: -9.7794
x_integral: 0.0000
y_integral: 0.0018
z_integral: -0.0391
temperature: 44.7368
range_m_s2: 156.9064
scaling: 0.0048
x_raw: 44
y_raw: -122
z_raw: -2064
temperature_raw: 3515
device_id: 1442082
TOPIC: sensor_accel instance 0 #4
timestamp: 45670381
integral_dt: 4013
error_count: 0
x: 0.0179
y: 0.4408
z: -9.7816
x_integral: 0.0000
y_integral: 0.0017
z_integral: -0.0393
temperature: 44.7673
range_m_s2: 156.9064
scaling: 0.0048
x_raw: 47
y_raw: -121
z_raw: -2065
temperature_raw: 3526
device_id: 1442082
TOPIC: sensor_accel instance 0 #5
timestamp: 45730379
integral_dt: 4000
error_count: 0
x: 0.0164
y: 0.4363
z: -9.7636
x_integral: 0.0000
y_integral: 0.0018
z_integral: -0.0390
temperature: 44.7645
range_m_s2: 156.9064
scaling: 0.0048
x_raw: 49
y_raw: -123
z_raw: -2062
temperature_raw: 3525
device_id: 1442082
- uorb top 指令
uorb top指令用来实时显示每个主题的发布频率,输出如下:
nsh> uorb top
update: 1s, num topics: 86
TOPIC NAME INST #SUB #MSG #LOST #QSIZE
sensor_baro 0 2 66 22 1
sensor_baro 1 1 67 0 1
sensor_mag 0 1 42 0 1
vehicle_gps_position 0 6 4 11 1
sensor_mag 1 1 108 8 1
sensor_accel 0 1 248 0 1
sensor_gyro 0 2 248 0 1
sensor_gyro 1 2 238 7 1
sensor_mag 2 1 99 0 1
sensor_accel 1 1 223 0 1
sensor_mag 3 1 97 2 1
sensor_accel 2 1 250 2 1
sensor_gyro 2 2 250 2 1
adc_report 0 1 99 0 1
system_power 0 2 99 16 1
vehicle_control_mode 0 7 4 0 1
actuator_controls_0 0 7 248 1022 1
sensor_combined 0 6 248 927 1
sensor_preflight 0 1 248 0 1
battery_status 0 6 82 218 1
vehicle_status 0 8 4 4 1
actuator_armed 0 7 4 2 1
safety 0 1 41 0 1
vehicle_local_position 0 7 248 712 1
vehicle_attitude 0 5 248 836 1
vehicle_status_flags 0 0 83 0 1
其中,每列分别是:主题名称,多实例索引,订阅者数量,发布频率,丢包数(所有订阅者合起来的)和队列大小。
- 多实例
uORB提供了一种通过orb_advertise_multi函数来发布同一个主题的多个独立实例的机制。该函数将会返回一个实例索引给发布者。订阅者必须使用orb_subscribe_multi函数并提供实例索引来指定订阅哪个实例(使用orb_subscribe可以订阅第一个实例)。拥有多个实例是十分有用的,比如系统存在多个同类型的传感器时。
注意对于同一主题,不要混淆orb_advertise_multi和orb_advertise。
完整的API在src/modules/uORB/uORBManager.hpp中给出。 - 问题和陷阱
下面是几种常见的问题和陷阱:
- 主题没有被发布:确保每个ORB_ID()对应好。有一点比较重要的是必须在orb_publish函数所在的任务中调用orb_subscribe和orb_unsubscribe。
- 必须使用orb_unsubscribe和orb_unadvertise来清理订阅和广播。
- 成功调用orb_check或px4_poll后必须使用orb_copy()函数,否则下一个阻塞将会立即返回。
- 在主题被广播之前就订阅该主题是没有任何问题的。
- orb_check()和px4_poll()只对订阅后的信息发布返回true。这对不是规律性发布的主题是很重要的。如果一个订阅者需要使用前一组数据,则在orb_subscribe()之后调用orb_copy()即可(在主题没有被发布时,orb_copy()函数会执行失败)。
上文中的内容主要是官方文档里的,给出了uORB的概述,但是没有给出关键函数的解析,由于这部分比较重要,下一篇中笔者将结合代码和文档给出uORB流程和其中关键函数的解析。
转载于:https://www.cnblogs.com/spyplus/p/7401555.html
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