python-can J1939过滤掩码

Question

我一直在使用带有MCP2515 CAN总线设备的Raspberry在用python广播时读取J1939消息的全部值。

我想过滤J1939消息，但我并没有忘记can掩码的含义和我是如何不一致的。在python的文档中，说：

返回与至少一个筛选器匹配的所有邮件。如果筛选器为无长度序列或零长度序列，则所有消息都匹配。

[{"can_id": 0x11, "can_mask": 0x21, "extended": False}]

尽管我理解这个“无”部分，但我不知道如何识别我的ID消息的掩码

示例：

我只想通过脚本获取ID为"0xCF00400“和”0x18Fe927“的消息。

import can

# CAN Setting
can_interface = 'can0'
bus = can.interface.Bus(can_interface, bustype='socketcan_native')

while True:
     message = bus.recv()

     bus.set_filters([{"can_id":0xF004 , "can_mask": ?? , "extended": True},
                      {"can_id":0xfee9 , "can_mask": ?? , "extended": True}])

如何填充每个变量以及如何确定ID的掩码？

更新03/10/2021

我已经尝试了下面的代码，但仍然返回所有消息。

import can

# CAN Setting
can_interface = 'can0'

can_filters = [{"can_id":0xCF00400, "can_mask": 0, "extended": True},
               {"can_id":0x18fee927, "can_mask": 0, "extended": True}]

bus = can.interface.Bus(can_interface, bustype='socketcan_native',can_filters=can_filters)

while True:
     message = bus.recv()
     print(message)

输出：

Timestamp: 1615382511.238233    ID: 18fee500    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.238893    ID: 18fef100    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.247038    ID: 18fef100    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.247611    ID: 18fee500    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.248222    ID: 18fee900    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.248868    ID: 0cf00400    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.257056    ID: 0cf00400    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.257623    ID: 18fee900    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.258223    ID: 18fef100    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.258827    ID: 18fee500    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.267039    ID: 18fee500    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.267624    ID: 18fef100    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.268229    ID: 0cf00400    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.268835    ID: 18fee900    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.277035    ID: 18fee900    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.277620    ID: 0cf00400    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.278220    ID: 18fee500    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0
Timestamp: 1615382511.278823    ID: 18fef100    X                DLC:  8    ff ff ff ff ff ff ff ff     Channel: can0

Answer 1

您可以使用"can_id":0xCF00400, "can_mask": 0xFFFFFFF对所需的cob ID进行有效的筛选(在内核级别)，而不需要掩码/过滤器。0xFFFFFFF的掩码(所有掩码位设置为1)需要在can_id上完全匹配。

bus.set_filters([{"can_id":0xCF00400, "can_mask": 0xFFFFFFF, "extended": True},
                 {"can_id":0x18fee927, "can_mask": 0xFFFFFFF, "extended": True}])

例如，文件上说：

过滤器匹配，当<received_can_id> & can_mask == can_id & can_mask。如果也设置了extended，那么它只匹配<received_is_extended> == extended中的消息。否则，它只基于仲裁ID和掩码匹配所有消息。

举个例子：

# The following just equals zero
0xCF00400 & 0 == 0 # True

# The following equals 0xCF00400 (217056256 in decimal) exactly
0xCF00400 & 0xFFFFFFF == 0xCF00400 # True
0xCF00400 & 0xFFFFFFF == 217056256 # True

# The following can_id would not get through the filter + mask:
0x18fee500 & 0xFFFFFFF == 0xCF00400 & 0xFFFFFFF # False

# The following obviously would get through the filter + mask:
0xCF00400 & 0xFFFFFFF == 0xCF00400 & 0xFFFFFFF # True

我会将bus.set_filters()放在while True循环之前，在bus.recv之前。这是一个设置，所以您只需要在开始时设置一次。

您最好在初始化总线时添加它，如下所示：

can_filters = [{"can_id":0xCF00400, "can_mask": 0xFFFFFFF, "extended": True},
               {"can_id":0x18fee927, "can_mask": 0xFFFFFFF, "extended": True}]

bus = can.Bus(
    interface="socketcan",
    channel="can0",
    can_filters=can_filters
)

而且，我相信bustype='socketcan_native'是已弃用赞成interface="socketcan"的。我已经成功地使用了后者一段时间，没有任何警告信息。