PLAN.txt

Transmissions:
	send():
	Managed function that selects next available TXB, takes uint32_t msgid + data buffer + data count + message priority
	- Tags a TXB as in use, irq handler for TXB IRQs will untag it later
	- Sends RTS command over SPI
	- Replies with TXB# used.
	query() sends a message on next available TXB with RTR enabled.

IRQ handler:
	- Notifies of latest issue
	- irq handler function manages the MCP2515_IRQ_FLAGGED state; user should not do so except setting in an IRQ firing.
	- Replies a bitmap of MCP2515_IRQ_TX, RX, WAKEUP, ERROR, HANDLED
	- HANDLED can be used as a shortcut to indicate nothing further is needed
	- ERROR alone means a bus error; can_read_error(MCP2515_EFLG) can indicate which
	- ERROR + RX means MERRF or overflow
	- ERROR + TX means MERRF
	- RX means one of the buffers has new data (mcp2515_buf says which)
	- TX means the latest TX completed (mcp2515_buf says which)

Receives:
	rx_pending() function checks if anything is available
	recv() doesn't care about RXB#, just replies with data length & populates data buffer + uint32_t msgid
	ioctl() with some options - ROLLOVER, standard-only vs. standard+extended msgid reception
	setmask() sets 1 of the 2 acceptance masks
	setfilter() takes an RXB#, a filter# and a filter