CAN filter mask

[tjwasiak]

I would like to kindly ask if it is possible to set custom mask for CAN filters? Upon setting filter using StartMsgFilter (PASS or BLOCK - it does not matter) mask is set to 0xFFFF.

[BrianHumlicek]

I would like to kindly ask if it is possible to set custom mask for CAN filters? Upon setting filter using StartMsgFilter (PASS or BLOCK - it does not matter) mask is set to 0xFFFF.

You should be able to specify any ushort for the mask and use a hard cast to pass it in.

[joeservo]

not very clear. maskMsg, patternMsg, flowControlMsg. why is there three?

with FLOW_CONTROL_FILTER type it seems only patternMsg matters, this exact value passes. nothing in the maskMsg seems to matter.

with PASS_FILTER type i get errors not matter whats in the 3.

trying to pass all 7xx messages.

[BrianHumlicek]

I was mistaken in my comment specifying a ushort and a hard cast to pass it in.

You could try this
var filter = new MessageFilter()
{
Mask = 0xF00,
Pattern = 0x700,
FilterType = Filter.PASS_FILTER
};

As for why there are three filter parameters, you should reference the SAE J2534 standard. I didn't create it, I just follow it.

Brian

[tjwasiak]

Thank you for clarification. Did some tests today and got it to work as I need.

[BrianHumlicek]

Also, for anyone else that reads this, I don't remember where I read it, but I seem to remember somewhere that wildecards (eg: mask other than 0xFF) are not supported in the mask. I think that is a totally ridiculous design decision, but some Drewtech drivers won't use them.

[joeservo]

PASS_FILTER doesnt work with a GM MDI2 or a scanmatik2. both give invlalid_filter_id or invalid_msg errors. it seems to work with an intrepidcs valuecan4-2.

[tjwasiak]

Scanmatik 3 works correctly - at least with mask 0x5FF (useful when working with GM ECUs sending data using both 0x7E8 and 0x5E8).
I can try Openport 2.0 and old GM MDI later...

EDIT: I should mention I am using raw CAN, not ISO15765.

[joeservo]

if you can provide some sample code snippets i'll forever be grateful. i tried connecting as can instead of iso using a different dot net dll with the same results, havent tried on this one.

gm mdi clone did not work for me either.

[joeservo]

i tried connecting as protocol.CAN and got better, mixed results.

pass_filter
intrepidcs vcan4 works like its supposed to
gm MDI2 does accept anything other than a mask of FF,FF,FF,FF

also discovered as a protocol.iso15765 GM MDI2 doesnt let you have any duplicate flowcontrol values in the filters. it seems this device is not flexible at all.

[BrianHumlicek]

Iso15765 is a transport layer protocol that runs over CAN. If you want to do any sniffing or RE, you usually have to resort to connecting as raw CAN and you will have to manually decode the iso frames. This is because the iso flow control filters actually cause the tool to send a flow control response which will conflict with the target network nodes. You may be able to find a software tool that will decode the frames for you. Maybe this would be a good addition to this library; create a software iso15765 decoder for sniffing.

Brian