如何发送或接收CAN数据

如何发送或接收 CAN 数据

目的

本文介绍如何使用 can-utils [1 ]包在 SocketCAN 接口上发送/接收数据。

can-utils 包含一些用于 Linux®SocketCAN 子系统的用户空间实用程序。它已集成在STM32微处理器系列的 SDK 中。在此示例中，仅使用到 cansend 和 candump，但软件包中还提供了许多其他的工具。

准备条件

至少需要两个设备才能在 CAN 网络上进行通信。要实现这种配置，请在同一 CAN 总线上连接两个设备。然后，从一个节点发送数据，并在另一节点上接收数据。

在开始通信之前，必须在每块板上配置并启用 SocketCAN 接口。请参阅如何设置 SocketCAN 接口。

在CAN总线上发送数据

要发送单个帧，请使用 cansend 实用程序：

	Board $> cansend can0 123#1122334455667788

获取 cansend 实用程序中的使用帮助信息：

	Board $> cansend -h
	Usage: cansend <device> <can_frame>

如果出现帧错误，请尝试下面的操作：

	    <can_id>#{R|data}          for CAN 2.0 frames
	  	<can_id>##<flags>{data}    for CAN FD frames

	<can_id> can have 3 (SFF) or 8 (EFF) hex chars
	{data} has 0..8 (0..64 CAN FD) ASCII hex-values (optionally separated by '.')
	<flags> a single ASCII Hex value (0 .. F) which defines canfd_frame.flags

	e.g. 5A1#11.2233.44556677.88/123#DEADBEEF/5AA#/123##1/213##311
	   1F334455#1122334455667788/123#R for remote transmission request.

在CAN总线上接收数据

要实时显示总线上收到的消息列表，请使用 candump 实用程序：

	Board $> candump can0
	can0  123   [8] 11 22 33 44 55 66 77 88

在 candump 实用程序上获取帮助信息：

	Board $> candump -h

	Usage: candump [options] <CAN interface>+
	   (use CTRL-C to terminate candump)

	Options: -t <type>   (timestamp: (a)bsolute/(d)elta/(z)ero/(A)bsolute w date)
	         -c          (increment color mode level)
	         -i          (binary output - may exceed 80 chars/line)
	         -a          (enable additional ASCII output)
	         -S          (swap byte order in printed CAN data[] - marked with '`' )
	         -s <level>  (silent mode - 0: off (default) 1: animation 2: silent)
	         -b <can>    (bridge mode - send received frames to <can>)
	         -B <can>    (bridge mode - like '-b' with disabled loopback)
	         -u <usecs>  (delay bridge forwarding by <usecs> microseconds)
	         -l          (log CAN-frames into file. Sets '-s 2' by default)
	         -L          (use log file format on stdout)
	         -n <count>  (terminate after receiption of <count> CAN frames)
	         -r <size>   (set socket receive buffer to <size>)
	         -D          (Don't exit if a "detected" can device goes down.
	         -d          (monitor dropped CAN frames)
	         -e          (dump CAN error frames in human-readable format)
	         -x          (print extra message infos, rx/tx brs esi)
	         -T <msecs>  (terminate after <msecs> without any reception)

	Up to 16 CAN interfaces with optional filter sets can be specified on the commandline in the form: <ifname>[,filter]*

	Comma separated filters can be specified for each given CAN interface:
	 <can_id>:<can_mask> (matches when <received_can_id> & mask == can_id & mask)
	 <can_id>~<can_mask> (matches when <received_can_id> & mask != can_id & mask)
	 #<error_mask>       (set error frame filter, see include/linux/can/error.h)
	 [j|J]               (join the given CAN filters - logical AND semantic)

	CAN IDs, masks and data content are given and expected in hexadecimal values.
	When can_id and can_mask are both 8 digits, they are assumed to be 29 bit EFF.
	Without any given filter all data frames are received ('0:0' default filter).

	Use interface name 'any' to receive from all CAN interfaces.

	Examples:
	candump -c -c -ta can0,123:7FF,400:700,#000000FF can2,400~7F0 can3 can8
	candump -l any,0~0,#FFFFFFFF    (log only error frames but no(!) data frames)
	candump -l any,0:0,#FFFFFFFF    (log error frames and also all data frames)
	candump vcan2,92345678:DFFFFFFF (match only for extended CAN ID 12345678)
	candump vcan2,123:7FF (matches CAN ID 123 - including EFF and RTR frames)
	candump vcan2,123:C00007FF (matches CAN ID 123 - only SFF and non-RTR frames)

硬件自检

在内部环回测试模式下，FDCAN将发送的消息作为接收消息进行处理。此选项用于硬件自检（无需在 CAN 总线上连接外部 CAN 节点）。

要在回环模式下配置和启用 SocketCAN，请执行以下操作：

	Board $> ip link set can0 up type can bitrate 1000000 dbitrate 2000000 fd on loopback on
	[ 78.700698] m_can 4400e000.can can0: bitrate error 0.3%
	[ 78.704568] m_can 4400e000.can can0: bitrate error 1.6%
	[ 78.710140] IPv6: ADDRCONF(NETDEV_CHANGE): can0: link becomes ready

要在同一接口上发送和接收消息，请按照下列步骤操作：

	Board $> candump can0 -L &
	[1] 475
	Board $> cansend can0 300#AC.AB.AD.AE.75.49.AD.D1
	(1539944874.949723) can0 300#ACABADAE7549ADD1
	(1539944874.949683) can0 300#ACABADAE7549ADD1

参考

CAN-UTILS信息，github.com上的README