如何解决python-can J1939过滤面罩
我一直在使用带有 MCP2515 CAN 总线设备的 RaspBerry 工作,用于在使用 python 广播时读取 J1939 消息的整个值。
我想过滤 J1939 消息,但我不明白 can-mask 的含义以及我如何发现它。在 python-can 的文档中说:
返回匹配至少一个过滤器的所有消息。如果过滤器 为 None 或零长度序列,所有消息都匹配。
[{"can_id": 0x11,"can_mask": 0x21,"extended": False}]
即使我理解了这个“无”部分,我还是不明白如何识别我的 ID 消息的掩码
示例:
我只想通过脚本获取 ID 为“0xCF00400”和“0x18fee927”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,"extended": True}])
我应该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,{"can_id":0x18fee927,"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
解决方法
您可以使用 "can_id":0xCF00400,"can_mask": 0xFFFFFFF
高效过滤(在内核级别)您想要的 cob ID,无需掩码/过滤器。 0xFFFFFFF
的掩码(所有掩码位设置为 1)要求与 can_id 完全匹配。
bus.set_filters([{"can_id":0xCF00400,"can_mask": 0xFFFFFFF,"extended": True},{"can_id":0x18fee927,"extended": True}])
例如,文档说:
过滤器匹配,当
<received_can_id> & can_mask == can_id & can_mask
。
如果 extended
也被设置,它只匹配消息
<received_is_extended> == extended
。否则它匹配每个
仅基于仲裁 ID 和掩码的消息。
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,以及 bus.recv
之前。这是一个设置,所以你只需要在开始时设置一次。
最好在初始化总线时添加它,如下所示:
can_filters = [{"can_id":0xCF00400,"extended": True}]
bus = can.Bus(
interface="socketcan",channel="can0",can_filters=can_filters
)
此外,我相信 bustype='socketcan_native'
是 deprecated 支持 interface="socketcan"
。我已经成功使用后者很长一段时间了,并且没有任何警告消息。
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