关于candump 命令中 filter 过滤的解释

原创于 2024-03-08 16:40:45 发布 · 1.7k 阅读

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文章详细解释了如何使用candump命令针对CAN接口进行数据帧过滤，区分标准帧、扩展帧和远程帧，并通过掩码指定接收特定CANID。内容涵盖了CANID的11位和29位格式，以及数据过滤的逻辑操作。

Filters:
  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 the can_id is 8 digits long the CAN_EFF_FLAG is set for 29 bit EFF format.
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 vcan2,12345678: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)

1、关于 canid 是标准 11位还是扩展 29位
例如 candump vcan2,123:C00007FF (matches CAN ID 123 - only SFF and non-RTR frames)
因为 mask 掩码是 C00007FF 说明只支持11位(7FF),其他位与的时候都清零了，所以
“only SFF and non-RTR frames” 表示只包括标准帧（Standard Frame Format，SFF）和非远程帧（non-RTR frames）。

再例如 candump vcan2,123:7FF
candump 命令将监听名为 vcan2 的虚拟 CAN 接口，并只捕获 CAN ID 为 123 的消息，包括扩展帧（EFF）和远程帧（RTR）消息。

2、看下 canid 是扩展29位
candump vcan2,12345678:DFFFFFFF
(match only for extended CAN ID 12345678) 只支持扩展帧，且can id 是 12345678。

3、can 标准帧
标准帧（Standard Frame Format，SFF）

4、can 扩展帧
扩展帧（Extended Frame Format）

5、can 远程帧
远程帧（Remote Frame）

6、can 数据帧
数据帧（Data Frame）

7、数据过滤的公式是

<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)