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133 lines
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133 lines
6.4 KiB
Markdown
# CAN (DroneCAN & Cyphal)
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[Controller Area Network (CAN)](https://en.wikipedia.org/wiki/CAN_bus) is a robust wired network that allows drone components such as flight controller, ESCs, sensors, and other peripherals, to communicate with each other.
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It is particularly recommended on larger vehicles.
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## 综述
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CAN it is designed to be democratic and uses differential signaling.
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For this reason it is very robust even over longer cable lengths (on large vehicles), and avoids a single point of failure.
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CAN 还允许来自外设的状态反馈，并通过总线方便的进行固件升级。
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PX4 支持与 CAN 设备通信的两个软件协议：
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- [DroneCAN](../dronecan/index.md): PX4 推荐大多数常见的设置。
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它得到了 PX4 的很好支持，是一个成熟的产品，具有广泛的外围支持，并经过多年的测试。
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- [Cyphal](https://opencyphal.org)：PX4 支持是一个“在进行中的工作”。
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Cyphal 是一种更新的协议，允许更多的灵活性和配置，尤其是对于较大和较复杂的载具。
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它还没有被广泛应用。
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:::info
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DroneCAN 和 Cyphal 都是早先一个叫做UAVCAN的项目。
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在2022年，该项目分为两个部分：原始版本的 UAVCAN (UAVCAN v0) 更名为 DroneCAN，较新的 UAVCAN v1 更名为 Cyphal。
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这两项协议之间的差异在[Cyphal vs. DroneCAN](https://forum.opencyphal.org/t/cyphal-vs-dronecan/1814)中作了概述。
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:::
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PX4不支持KDECAN等无人驾驶飞机的其他CAN软件协议(撰写时)。
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## 布线
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CAN 网络的接线对于 DroneCAN 和 Cyphal/CAN 是一样 (实际上对所有的 CAN 网络都一样)。
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Devices within a network are connected in a _daisy-chain_ in any order (this differs from UARTs peripherals, where you attach just one component per port).
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:::warning
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Don't connect each CAN peripheral to a separate CAN port!
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Unlike UARTs, CAN peripherals are designed to be daisy chained, with additional ports such as `CAN2` used for [redundancy](redundancy).
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:::
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在链的任一端，应该在两个数据线之间连接一个 120Ω 的终端电阻。
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飞控和一些 GNSS 模块为了方便使用内置了终端电阻， 因此应该放在链的终端。
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否则，你可以使用终端电阻，比如 [Zubax Robotics 的这款](https://shop.zubax.com/products/uavcan-micro-termination-plug?variant=6007985111069)。如果你有JST - GH压接工具，也可以自己焊接一个。
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下图显示了一个 CAN 总线连接飞控到 4 个 CAN 电调和一个 GNSS 的示例。
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It includes a redundant bus connected to `CAN 2`.
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图中未显示任何电源接线。
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参考制造商的说明，确认组件是否需要单独供电，还是可以通过 CAN 总线供电。
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:::info
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For more information, see [Cyphal/CAN device interconnection](https://wiki.zubax.com/public/cyphal/CyphalCAN-device-interconnection?pageId=2195476) (kb.zubax.com).
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虽然本文是以 Cyphal 协议为基础编写的，但同样适用于 DroneCAN 硬件和任何其他 CAN 设置。
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如需了解更复杂的场景，请参考 [论CAN总线拓扑结构与终端匹配](https://forum.opencyphal.org/t/on-can-bus-topology-and-termination/1685)。
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:::
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### 连接器
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Pixhawk标准兼容的 CAN 设备使用 4 引脚的 JST-GH 连接器为 CAN。
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在连线接线时，有两个连接器用于输入和输出（飞行控制器除外和一些内置终止的全球导航卫星系统（GNSS）设备除外）； 它仅有一个JST-GH连接器)。
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其他(非Pixhawk兼容的)设备可能使用不同的连接器。
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然而，只要设备固件支持DroneCAN 或Cyphal，它就可以使用。
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### 冗余
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DroneCAN 和 Cyphal/CAN支持使用第二个(冗余) CAN 接口。
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这是完全可选的，但会增加连接的强度。
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Pixhawk flight controllers come with 2 CAN interfaces; if your peripherals support 2 CAN interfaces as well, it is recommended to wire both up for increased safety.
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### Flight Controllers with Multiple CAN Ports
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[Flight Controllers](../flight_controller/index.md) may have up to three independent CAN ports, such as `CAN1`, `CAN2`, `CAN3` (neither DroneCAN or Cyphal support more than three).
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Note that you can't have both DroneCAN and Cyphal running on PX4 at the same time.
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:::tip
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You only _need_ one CAN port to support an arbitrary number of CAN devices using a particular CAN protocol.
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Don't connect each CAN peripheral to a separate CAN port!
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:::
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Generally you'll daisy all CAN peripherals off a single port, and if there is more than one CAN port, use the second one for [redundancy](redundancy).
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If three are three ports, you might use the remaining network for devices that support another CAN protocol.
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The documentation for your flight controller should indicate which ports are supported/enabled.
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At runtime you can check what DroneCAN ports are enabled and their status using the following command on the [MAVLink Shell](../debug/mavlink_shell.md) (or some other console):
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```sh
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uavcan status
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```
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Note that you can also check the number of supported CAN interfaces for a board by searching for `CONFIG_BOARD_UAVCAN_INTERFACES` in its [default.px4board](https://github.com/PX4/PX4-Autopilot/blob/main/boards/px4/fmu-v6xrt/default.px4board#) configuration file.
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## 固件
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CAN 外围设备可以运行专有或开源固件(请检查制造商指南以确认所需的设置)。
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PX4 可以构建在支持的 CAN 硬件上作为开源的 DroneCAN 固件运行。
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更多信息请参考 [PX4 DroneCAN 固件](../dronecan/px4_cannode_fw.md)。
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## 支持和配置
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[DroneCAN 设置和配置](../dronecan/index.md)
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[PX4 DroneCAN 固件](../dronecan/px4_cannode_fw.md)
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## 视频
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### DroneCAN
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关于 DroneCAN (UAVCANv0) 的介绍和在 QGroundControl 中设置的实用示例：
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<lite-youtube videoid="IZMTq9fTiOM" title="Intro to DroneCAN (UAVCANv0) and practical example with setup in QGroundControl"/>
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### Cyphal
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无人机的 UAVCAN v1 (Cyphal) - PX4 开发者峰会虚拟2020
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<lite-youtube videoid="6Bvtn_g8liU" title="UAVCAN v1 for drones — PX4 Developer Summit Virtual 2020"/>
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---
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在NXP UAVCAN板上使用UAVCAN v1和PX4入门——2020年PX4开发者峰会线上会议
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<lite-youtube videoid="MwdHwjaXYKs" title="Getting started using UAVCAN v1 with PX4 on the NXP UAVCAN Board"/>
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---
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UAVCAN：一个高度可靠的发布-订阅协议，用于硬实时车辆内网络 — PX4 开发者虚拟峰会 2019
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<lite-youtube videoid="MBtROivYPik" title="UAVCAN: a highly dependable publish-subscribe protocol for hard ..."/>
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