CAN::write() uses mailbox 16 if the ID is standard, which is configured as a receive mailbox. I think this should be 8?

I think this works because the FSP only checks if the TRMREQ flag is set, which it won't be for a receive mailbox, and then configures it for transmit.

I'm guessing that all future receives will come via mailbox 17 onwards, as 16 is no longer configured as a receive, which would break any filters assigned to 16.