模块参考：通信（Communication）

frsky_telemetry

Source: drivers/telemetry/frsky_telemetry

FrSky 数传支持，会自动检测使用 D.PORT 还是 S.PORT 协议。

Usage

frsky_telemetry <command> [arguments...]
 Commands:
   start
     [-d <val>]  Select Serial Device
                 values: <file:dev>, default: /dev/ttyS6
     [-t <val>]  Scanning timeout [s] (default: no timeout)
                 default: 0
     [-m <val>]  Select protocol (default: auto-detect)
                 values: sport|sport_single|sport_single_invert|dtype, default:
                 auto
   stop
   status

mavlink

Source: modules/mavlink

描述

此模块实现了 MAVLink 协议，该协议可在串口或 UDP 网络上使用。它通过 uORB 实现与系统的通信：部分消息会在此模块中直接进行处理（例，mission protocol），其它消息将通过 uORB 发布出去（例，vehicle_command）。

流（Stream）被用来以特定速率发送周期性的消息，例如飞机姿态信息。在启动 mavlink 实例时可以设定一个模式，该模式定义了所启用的流集合的发送速率。对于一个正在运行的实例而言，可以使用 mavlink stream 命令来配置流。

可以存在多个该模块的实例，每个实例连接到一个串口设备或者网络端口。

实现

命令的具体实现使用了两个线程，分别为数据发送线程和接收线程。发送线程以一个固定的速率运行，并会在组合带宽（combined bandwidth）高于设定速率(-r)，或者物理链路出现饱和的情况下动态降低信息流的发送速率。可使用 mavlink status 命令检查是否发生降速，如果 rate mult 小于 1 则发生了降速。

Careful: 两个线程会共同访问和修改某些数据，在修改代码或者扩展功能是需要考虑到这一点以避免出现资源竞争（race conditions）或者造成数据损坏（corrupt data）。

示例

在 ttyS1 串口启动 mavlink ，并设定波特率为 921600、最大发送速率为 80kB/s：

mavlink start -d /dev/ttyS1 -b 921600 -m onboard -r 80000

在 UDP 端口 14556 启动 mavlink 并启用 50Hz 的 HIGHRES_IMU 消息：

mavlink start -u 14556 -r 1000000
mavlink stream -u 14556 -s HIGHRES_IMU -r 50

Usage

mavlink <command> [arguments...]
 Commands:
   start         Start a new instance
     [-d <val>]  Select Serial Device
                 values: <file:dev>, default: /dev/ttyS1
     [-b <val>]  Baudrate (can also be p:<param_name>)
                 default: 57600
     [-r <val>]  Maximum sending data rate in B/s (if 0, use baudrate / 20)
                 default: 0
     [-u <val>]  Select UDP Network Port (local)
                 default: 14556
     [-o <val>]  Select UDP Network Port (remote)
                 default: 14550
     [-t <val>]  Partner IP (broadcasting can be enabled via MAV_BROADCAST
                 param)
                 default: 127.0.0.1
     [-m <val>]  Mode: sets default streams and rates
                 values:
                 custom|camera|onboard|osd|magic|config|iridium|minimal|extvsisi
                 on, default: normal
     [-n <val>]  wifi/ethernet interface name
                 values: <interface_name>
     [-c <val>]  Multicast address (multicasting can be enabled via
                 MAV_BROADCAST param)
                 values: Multicast address in the range
                 [239.0.0.0,239.255.255.255]
     [-f]        Enable message forwarding to other Mavlink instances
     [-w]        Wait to send, until first message received
     [-x]        Enable FTP
     [-z]        Force hardware flow control always on
     [-Z]        Force hardware flow control always off
   stop-all      Stop all instances
   status        Print status for all instances
     [streams]   Print all enabled streams
   stream        Configure the sending rate of a stream for a running instance
     [-u <val>]  Select Mavlink instance via local Network Port
     [-d <val>]  Select Mavlink instance via Serial Device
                 values: <file:dev>
     -s <val>    Mavlink stream to configure
     -r <val>    Rate in Hz (0 = turn off, -1 = set to default)
   boot_complete Enable sending of messages. (必须) 作为启动脚本的最后一步被调用。

micrortps_client

Source: modules/micrortps_bridge/micrortps_client

Usage

micrortps_client <command> [arguments...]
 Commands:
   start
     [-t <val>]  Transport protocol
                 values: UART|UDP, default: UART
     [-d <val>]  Select Serial Device
                 values: <file:dev>, default: /dev/ttyACM0
     [-b <val>]  Baudrate (can also be p:<param_name>)
                 default: 460800
     [-p <val>]  Poll timeout for UART in ms
     [-l <val>]  Limit number of iterations until the program exits
                 (-1=infinite)
                 default: 10000
     [-w <val>]  Time in ms for which each iteration sleeps
                 default: 1
     [-r <val>]  Select UDP Network Port for receiving (local)
                 default: 2019
     [-s <val>]  Select UDP Network Port for sending (remote)
                 default: 2020
     [-i <val>]  Select IP address (remote)
                 values: <x.x.x.x>, default: 127.0.0.1
     [-f]        Activate UART link SW flow control
     [-h]        Activate UART link HW flow control
     [-v]        Add more verbosity
   stop
   status

uorb

Source: modules/uORB

描述

uORB is the internal pub-sub messaging system, used for communication between modules.

It is typically started as one of the very first modules and most other modules depend on it.

实现

No thread or work queue is needed, the module start only makes sure to initialize the shared global state. Communication is done via shared memory. The implementation is asynchronous and lock-free, ie. a publisher does not wait for a subscriber and vice versa. This is achieved by having a separate buffer between a publisher and a subscriber.

The code is optimized to minimize the memory footprint and the latency to exchange messages.

The interface is based on file descriptors: internally it uses read, write and ioctl. Except for the publications, which use orb_advert_t handles, so that they can be used from interrupts as well (on NuttX).

Messages are defined in the /msg directory. They are converted into C/C++ code at build-time.

If compiled with ORB_USE_PUBLISHER_RULES, a file with uORB publication rules can be used to configure which modules are allowed to publish which topics. This is used for system-wide replay.

示例

Monitor topic publication rates. Besides top, this is an important command for general system inspection:

uorb top

Usage

uorb <command> [arguments...]
 Commands:
   start
   status        Print topic statistics
   top           Monitor topic publication rates
     [-a]        print all instead of only currently publishing topics with
                 subscribers
     [-1]        run only once, then exit
     [<filter1> [<filter2>]] topic(s) to match (implies -a)