The move-in process is not atomic, in such a way that it is immediately cancelled by theinactivation of the destination mailbox (see Mailbox inactivation). In this case themailbox may remain partially updated, thus incoherent. The exception is if the move-indestination is a Rx FIFO message buffer; then the process cannot be cancelled.The BUSY Bit (least significant bit of the CODE field) of the destination message bufferis asserted while the move-in is being performed to alert the CPU that the message buffercontent is temporarily incoherent.49.5.6.2 Move-outThe move-out process is the copy of the content from a Tx Mailbox to the Tx SMB whena message for transmission is available (see Arbitration process). The move-out occurs inthe following conditions:• The first bit of Intermission field• During Bus Off state when TX Error Counter is in the 124 to 128 range• During Bus Idle state• During Wait For Bus Idle stateThe move-out process is not atomic. Only the CPU has priority to access the memoryconcurrently out of Bus Idle state. In Bus Idle, the move-out has the lowest priority to theconcurrent memory accesses.49.5.7 Data coherenceIn order to maintain data coherency and FlexCAN proper operation, the CPU must obeythe rules described in Transmit process and Receive process.49.5.7.1 Transmission abort mechanismThe abort mechanism provides a safe way to request the abort of a pending transmission.A feedback mechanism is provided to inform the CPU if the transmission was aborted orif the frame could not be aborted and was transmitted instead.Two primary conditions must be fulfilled in order to abort a transmission:• MCR[AEN] must be asserted.• The first CPU action must be the writing of abort code (0b1001) into the CODE fieldof the Control and Status word.Chapter 49 FlexCANMWCT101xS Series Reference Manual, Rev. 3, 07/2019NXP Semiconductors 1675
