CAN-BUS - how do I filter stuff ?

[jpcurrie]

@cory.j.fowler

@jpcurrie

I’ve swapped to ChipKit MAX32 with network shield, dual can-buses and a library written by Microchip.

Filtering works spot on.

That there actually looks pretty nifty… While you’ve moved on, I have found that filtering with this library works as expected.

To enable receiving everything without commenting out a section in the library, add the below after ‘CAN.begin();’ in the sketch…

CAN.init_Mask(0,1,0x00000000);
CAN.init_Filt(0,0,0x00000000);
CAN.init_Filt(1,1,0x00000000);

Setting all of the mask bits to 0 causes it to pass through the filter regardless of its setting… HOWEVER, there is a bit in the filter that sets EXCLUSIVELY whether or not to accept extended frames. The second value in the above functions sets that bit. That code sets up the first receive buffer mask to allow anything, then sets up the first filter to exclusively to allow all standard frames and finally sets the second filter to exclusively allow all extended frames.

Ideally, if you want to receive a specific frame ID, set the all mask bits to 1 and define the filter(s) for the specific ID(s) you are wanting.

That makes sense thanks. We should be able to accept both on each filter, anyway, PIC is my future!

I figured out that much but never got the filtering to work for a CANID, but I think I made a mistake with the MSB on the network I was using…

FWIW, the Microchip library is complete, but it needs a bit of work to wrap up the functions depending on each requirement, type of CAN network etc, I guess most of the non-std stuff would be like that anyway.