路由

这个主题解释了如何由 MAVLink 系统路由信息。

综述

一个 MAVLINK 网络由多种系统组成（无人机、地面站、天线追踪器等），这些系统可能由一个或多个组件（自动试验、相机、服务器等）组成。

Each system has a network-unique system ID, and each component has a system-unique component ID that can be used for addressing/routing. Both are values between 1 and 255.

消息可用于所有系统、特定系统、系统中的所有组件或系统内的特定组件。 协议界定了在报文有效载荷中能够(可选) 指定的两个8位字段，以表明发送/路由。 If the IDs are omitted or set to zero then the message is considered a broadcast (intended for all systems/components).

• target_system: System that should execute the command
• target_component: Component that should execute the command (requires target_system).

MAVLink components are expected to process messages that have a matching system/component ID and broadcast messages. They are expected to route/resend messages that are intended for other (or all) recipients to other active channels (i.e. MAVLink systems may be connected across different transports, connected by a MAVLink system that routes the messages). 广播消息已转发给所有尚未看到消息的通道。 Addressed messages are resent on a new channel iff the system has previously seen a message from the target on that channel (messages are not resent if the addressee is not known or is on the original/incoming channel).

WARNING

Forwarded messages must not be changed/repackaged by the forwarding system (the original message is passed to the new link).

INFO

Systems should, where possible, forward messages according to the routing rules even if they are unable to process them (e.g. signed messages that cannot be authenticated). Messages that are not supported/understood by the library should be forwarded as though they were broadcast messages (in this case the target system/component IDs cannot be read).

ID allocation

MAVLink does not provide mechanisms to automate allocation of system and component IDs. Instead these are manually allocated by the system integrator.

In order to reduce the chance of collisions (by convention):

• Autopilots on a MAVLink network are allocated sequentially increasing system IDs from 1 (1 is usually the default autopilot system ID).
• GCS and MAVLink developer APIs are allocated sequentially decreasing system IDs, starting from 255. Note that GCS will usually, but not always, have an ID in the upper range.
• Components can be allocated any unused ID in the range. Components usually have a default value based on their type, as mapped by MAV_COMPONENT.

WARNING

Code must not assume from the component ID that it knows the type of the component. The type of a component must be determined from its MAV_TYPE

Components should expose mechanisms to set their system and component IDs. Commonly a component may be configured to discover its system ID on boot by latching the system ID of the first autopilot HEARTBEAT that it discovers.

路由详细信息

A component should attempt to process a message locally if any of these conditions hold:

• The target_system field is omitted or has value 0 ("network broadcast").
• The target_system matches its system ID and the target_component field is omitted or has value 0 ("system broadcast").
• The target_system and target_component matches its system and component IDs.

Components that have multiple channels should forward a message to other channels if any of these conditions hold:

• It is a network broadcast message (target_system field omitted or zero).
• The target_system does not match the system ID and the component has previously seen a message from target_system on the link.
• The target_system matches its system ID and has a target_component field, and the component has seen a message from the target_system/target_component combination on the link.

INFO

Non-broadcast messages must only be forwarded to channels from which the component has previously received a message from the target system/component.

TIP

Components should also check for SYSTEM_TIME messages with a decrease in time_boot_ms, as this indicates that the system has rebooted. In this case it should clear stored routing information (and might perform other actions that are useful following a reboot - e.g. re-fetching parameters and home position etc.).

库支持

C 库 (mavgen)

The generated code for the MAVLink v1 C Library has no specific support for routing or working with target_system and target_component. To extract this information you will need to use the normal methods provided for reading payload fields, and match on the field names.

The MAVLink v2 generator for the C library has been updated to make it easier to get the destination system and component ID from the payload (when these are assigned). Specifically, the mavlink_msg_entry_t structure contains flags to tell you if the message contains target system/component information (FLAG_HAVE_TARGET_SYSTEM, FLAG_HAVE_TARGET_COMPONENT) and offsets into the payload that you can use to get these IDs (target_system_ofs and target_component_ofs, respectively). The MAVLink helper method const mavlink_msg_entry_t* mavlink_get_msg_entry(uint32_t msgid) can be used to get this structure from the message ID.

MAVLink 2 路由

Unsigned MAVLink 2 packets are routed in the same way as MAVLink 1 packets.

Routing Signed Packets

Signed packets should be routed in the same way as any other packet.

In particular, a routing system should:

• 不以任何方式更改电文(包括替换原始签字)。
• 即使不能被验证(甚至理解)，因此不能在当地加以处理，也按照正常规则提交信息。

路由接口

The MAVLink Router can be used to mix-and-match different IP protocols with serial ports in order to route MAVLink traffic.

更多信息

• MAVLink Routing in ArduPilot (ArduPilot DevGuide)