K60P100M100SF2RM Datasheet, PDF (1370/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional Description
• CPU reads the CODE field to check if the frame was either transmitted
(CODE=0b1000) or aborted (CODE=0b1001).
• It is necessary to clear the corresponding IFLAG in order to allow the MB to be
reconfigured.
48.4.6.2 Message Buffer Inactivation
Inactivation is a mechanism provided to protect the Mailbox against updates by the
FlexCAN internal processes, thus allowing the CPU to rely on Mailbox data coherence
after having updated it, even in Normal Mode.
Inactivation of transmission Mailboxes must be performed just when MCR[AEN] bit is
deasserted.
If a Mailbox is inactivated it participates in neither the arbitration process nor the
matching process until it is reactivated. See Section "Transmit Process" and Section
"Receive Process" for more detailed instruction on how to inactivate and reactivate a
Mailbox.
In order to inactivate a Mailbox the CPU must update its CODE field to INACTIVE
(either 0b0000 or 0b1000).
As the user is not able to synchronize the CODE field update with the FlexCAN internal
processes an inactivation can lead to undesirable results:
• a frame in the bus that matches the filtering of the inactivated Rx Mailbox may be
lost without notice, even if there are other Mailboxes with the same filter;
• a frame containing the message within the inactivated Tx Mailbox may be
transmitted without notice.
In order to eliminate such risk and perform a safe inactivation the CPU must use the
following mechanism along with the inactivation itself:
• for Tx Mailboxes, the Transmission Abort (see Section "Transmission Abort
Mechanism");
The inactivation automatically unlocks the Mailbox (see Section "Message Buffer Lock
Mechanism").
NOTE
Message Buffers that are part of the Rx FIFO cannot be
inactivated. There is no write protection on the FIFO region by
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K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.