Datasheet

SAM9263 [DATASHEET]
Atmel-6249N-ATARM-SAM9263-Datasheet_14-Mar-16
648
36.7.3 CAN Controller Message Handling
36.7.3.1 Receive Handling
Two modes are available to configure a mailbox to receive messages. In Receive Mode, the first message
received is stored in the mailbox data register. In Receive with Overwrite Mode, the last message received is
stored in the mailbox.
36.7.3.2 Simple Receive Mailbox
A mailbox is in Receive Mode once the MOT field in the CAN_MMRx has been configured. Message ID and
Message Acceptance Mask must be set before the Receive Mode is enabled.
After Receive Mode is enabled, the MRDY flag in the CAN_MSR is automatically cleared until the first message is
received. When the first message has been accepted by the mailbox, the MRDY flag is set. An interrupt is pending
for the mailbox while the MRDY flag is set. This interrupt can be masked depending on the mailbox flag in the
CAN_IMR global register.
Message data are stored in the mailbox data register until the software application notifies that data processing
has ended. This is done by asking for a new transfer command, setting the MTCR flag in the CAN_MCRx. This
automatically clears the MRDY signal.
The MMI flag in the CAN_MSRx notifies the software that a message has been lost by the mailbox. This flag is set
when messages are received while MRDY is set in the CAN_MSRx. This flag is cleared by reading the
CAN_MSRs register. A receive mailbox prevents from overwriting the first message by new ones while MRDY flag
is set in the CAN_MSRx. See Figure 36-11.
Figure 36-11. Receive Mailbox
Note: In the case of ARM architecture, CAN_MSRx, CAN_MDLx, CAN_MDHx can be read using an optimized ldm
assembler instruction.
Message 1 Message 2 lost Message 3
Message 3
Message 1
Reading CAN_MSRx
Reading CAN_MDHx & CAN_MDLx
Writing CAN_MCRx
MMI
(CAN_MSRx)
MRDY
(CAN_MSRx)
CAN BUS
(CAN_MDLx
CAN_MDHx)
MTCR
(CAN_MCRx)
Message ID = CAN_MIDx