Atmel Evaluation Kit for the SAM4E Series of Flash Microcontrollers ATSAM4E-EK ATSAM4E-EK Data Sheet
Product codes
ATSAM4E-EK
671
SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
Receive with Overwrite Mailbox
A mailbox is in Receive with Overwrite Mode once the MOT field in the CAN_MMRx has been configured.
Message ID and Message Acceptance masks must be set before Receive Mode is enabled.
Message ID and Message Acceptance masks must be set before 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 is masked depending on the mailbox flag in the CAN_IMR
global register.
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 is masked depending on the mailbox flag in the CAN_IMR
global register.
If a new message is received while the MRDY flag is set, this new message is stored in the mailbox data register,
overwriting the previous message. The MMI flag in the CAN_MSRx notifies the software that a message has been
dropped by the mailbox. This flag is cleared when reading the CAN_MSRx.
overwriting the previous message. The MMI flag in the CAN_MSRx notifies the software that a message has been
dropped by the mailbox. This flag is cleared when reading the CAN_MSRx.
The CAN controller may store a new message in the CAN data registers while the application reads them. To
check that CAN_MDHx and CAN_MDLx do not belong to different messages, the application must check the MMI
field in the CAN_MSRx before and after reading CAN_MDHx and CAN_MDLx. If the MMI flag is set again after the
data registers have been read, the software application has to re-read CAN_MDHx and CAN_MDLx (see
check that CAN_MDHx and CAN_MDLx do not belong to different messages, the application must check the MMI
field in the CAN_MSRx before and after reading CAN_MDHx and CAN_MDLx. If the MMI flag is set again after the
data registers have been read, the software application has to re-read CAN_MDHx and CAN_MDLx (see
Figure 33-12. Receive with Overwrite Mailbox
Chaining Mailboxes
Several mailboxes may be used to receive a buffer split into several messages with the same ID. In this case, the
mailbox with the lowest number is serviced first. In the receive and receive with overwrite modes, the field PRIOR
in the CAN_MMRx has no effect. If Mailbox 0 and Mailbox 5 accept messages with the same ID, the first message
is received by Mailbox 0 and the second message is received by Mailbox 5. Mailbox 0 must be configured in
Receive Mode (i.e., the first message received is considered) and Mailbox 5 must be configured in Receive with
Overwrite Mode. Mailbox 0 cannot be configured in Receive with Overwrite Mode; otherwise, all messages are
accepted by this mailbox and Mailbox 5 is never serviced.
mailbox with the lowest number is serviced first. In the receive and receive with overwrite modes, the field PRIOR
in the CAN_MMRx has no effect. If Mailbox 0 and Mailbox 5 accept messages with the same ID, the first message
is received by Mailbox 0 and the second message is received by Mailbox 5. Mailbox 0 must be configured in
Receive Mode (i.e., the first message received is considered) and Mailbox 5 must be configured in Receive with
Overwrite Mode. Mailbox 0 cannot be configured in Receive with Overwrite Mode; otherwise, all messages are
accepted by this mailbox and Mailbox 5 is never serviced.
If several mailboxes are chained to receive a buffer split into several messages, all mailboxes except the last one
(with the highest number) must be configured in Receive Mode. The first message received is handled by the first
mailbox, the second one is refused by the first mailbox and accepted by the second mailbox, the last message is
accepted by the last mailbox and refused by previous ones (see
(with the highest number) must be configured in Receive Mode. The first message received is handled by the first
mailbox, the second one is refused by the first mailbox and accepted by the second mailbox, the last message is
accepted by the last mailbox and refused by previous ones (see
Message 1
Message 2
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
Message 4
Message 2
Message 4