The library does support extended CAN frames, however I am still figuring out the library to its entity as I had to comment out a section in the library that sets certain bits so I can receive everything… I have already discovered a bug when trying to read extended frame IDs greater than 0x00007FFF. As for interrupts, the sample code that uses the Atmega’s interrupt handling doesn’t work the way the MCP2515 uses its /INT line. I discovered that the MCP2515 holds its /INT line low when the buffer is full, its not a one shot like the interrupt handler is expecting it to be. In essence, the /INT line remains low, the flag never gets set again because the interrupt handler never sees a falling edge, and the Arduino loops waiting for the flag to be set. Instead, I just monitor the pin and if it is low, I read the MCP2515. I’ve been able to monitor fast buses setup like this with no crashing. I’ve been working on this for about a week when I have the time… this was the first library for the MCP2515 I was able to get working. Out of the box, you should be able to receive standard frames.