Hello Toyomasa Watarai, I see you assigned to this question. I was wondering if you had any updates?

I have read more about the ID and masking when building the filters. I think I understand that well enough, it would still be nice to get some more information, but what I am still not sure of is how the filters should be implemented.

It appears you create message filter handles which I am guessing are sent to the peripheral in order to filter the incoming messages once they are created. It then appears use the read function (depending on API) to read from the buffer with the "handle" or filter passed with it so you only read the next available packet that passes that filter.

The best example I could find is using CMSIS, but is easy enough to read and compare to the mbed API.

can->reset(); // reset and clear all filters (accept all messages)
h1 = can->filter(0x100, 0x700, CANStandard); // Accept standard messages with id 0x100-0x1FF
h2 = can->filter(0x200, 0x7FF, CANStandard); // Accept standard message 0x200 as well
[...]
h2 = can->filter(0x300, 0x7FF, CANStandard, h2); // Accept standard message 0x300, overwrite 0x200
 
CANMessage msg = CANMessage();
int r = can.read(msg, h1); // Should only return messages with id 0x100-0x1FF
int r = can.read(msg, h2); // Should only return messages with id 0x300
int r = can.read(msg);     // Returns 0x100-0x1FF if pending, otherwise 0x300, otherwise any message

From this it appears I can make several "handles" and when reading I use them to filter the one or more messages I want to get during that reading.

Without testing this should work to read only the ID 270, correct?

handle = can.filter(0x270, 0x7FF, CANStandard);

CANMessage CANmes;

if(canBus.read(CANmes, handle)){
    //deal with message
}

It's not working... :-(

I'd be very interested to see an answer (I'm using LPC1768)...

It might be worth posting a new question to help get it noticed. I am surprised that the CAN interface does not have a clean

Here is a reference to somebody that coded their own way of adding filters. Looks a little complex, but at least it is a reference to a working method.

https://os.mbed.com/users/ym1784/code/CAN_MONITOR/file/fe1f886dff76/main.cpp

Looking at the documentation it looks like there might be a filter interface now. Not sure when this was added. https://docs.mbed.com/docs/mbed-os-api-reference/en/5.1/APIs/interfaces/digital/CAN/#api

  /** Filter out incomming messages
  *
  * @param id the id to filter on
  * @param mask the mask applied to the id
  * @param format format to filter on (Default CANAny)
  * @param handle message filter handle (Optional)
  *
  * @returns
  * 0 if filter change failed or unsupported,
  * new filter handle if successful
  */

  int filter(unsigned int id, unsigned int mask, CANFormat format = CANAny, int handle = 0);