FlexCAN Mailbox Configuration and Length

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FlexCAN Mailbox Configuration and Length

Contributor I


I am working on re-configuring FlexCAN Mailbox definitions for MPC5606B processor.
I am asked to make 32 Rx and 32 Tx Mailboxes ( 64 total ) able to receive/transmit messages with any IDs ( what means : Mask==0, Filter==0 ).

In the project I am working on all Mailboxes are defined using the following structure :
typedef struct
 uint8                                   length;
 Can_MbDirectionType       ioType;  /**< RX or TX */
 Can_FilterMaskType          filterMask;
 Can_IdType                        id;
}   Can_HardwareObjectType;
as an array of 56 objects of “Can_HardwareObjectType”,

For example ( just a couple of elements ) :

/* 2 - Message Name: BinaryEventConfigThreshold */
  8u,                                            /**< Length (bytes)  */
  CAN_DIR_RX,                         /**< Direction  */
  (Can_FilterMaskType)0x7ffu,   /** Filter */
  0x357u,                                     /**< CAN Id if Extended ORed with 0x80000000 */
 /* 3 - Message Name: D_Outputs */
  1u,                                             /**< Length (bytes)  */
  CAN_DIR_RX,                           /**< Direction  */
  (Can_FilterMaskType)0x7ffu,    /** Filter */
  0x311u,                                      /**< CAN Id if Extended ORed with 0x80000000 */

As I am expected to make all Mailboxes receive/transmit messages with any IDs, I am re-defining them like this :
For Rx Mailboxes :
  0u,                                          /**< Length (bytes)  */
  CAN_DIR_RX,                        /**< Direction  */
  (Can_FilterMaskType) 0x0,     /** Filter */
  0x0u,                                       /* CAN ID */
For Tx Mailboxes :
  0u,                                           /**< Length (bytes)  */
  CAN_DIR_TX,                         /**< Direction  */
  (Can_FilterMaskType) 0x0u,  /** Filter */
  0x0u,                                       /* CAN ID */

My questions :
  1)  Am I defining them right ?
  2)  What should I specify for “Mailbox Length” field if I want to use the Mailboxes for receiving/transmitting messages with any IDs ?

Any ideas ?

Thank you for your help.

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2 Replies

NXP TechSupport
NXP TechSupport

Hi Konstantin,

1)  Am I defining them right ?

It could be, if the MB is properly filled from your given structure. The MB area is following...


2 facts must be considered.

- if you want to receive all IDs with both standard and extended format at least 2 MBs must be configured for reception one with IDE bit cleared (standard ID) and second with IDE bit set (extended)

- if RX queue is disabled, MCR[BCC]=0, the received message will be stored always in the first prepared RX MB, others will be never used.

  2)  What should I specify for “Mailbox Length” field if I want to use the Mailboxes for receiving/transmitting messages with any IDs ?

Length does not depend on ID.

For a RX MB, length is don't care, it is written by module once message is moved-in based on message data payload.

For a TX MB, length specifies how many bytes will be transmitted.

BR, Petr

Contributor I

Hi Petr,

   Thank you for answering. Sorry for late reply : I was very busy.

    My MCR[BCC]==1 and I am using 29 bit mode ( IDE==1 ).

    Could you please shed some light upon the following :

    1) Why ( and physically where in memory ) do I need those 2 MBs ? Where in the memory I am supposed to allocate them ? Are they related to any buffers for storing received or prepared for transmit data ?

     2) Is a FIFO buffer a part of any mailbox ? In other words, so I need to allocate FIFO buffers myself, link to the mailboxes and implement their support programmatically myself ? Or all FIFO

operation is supported on the hardware level ?

     Thanks again ! You really help !


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