Can Message Transfer - Altera cyclone V Technical Reference

cv_5v4
2016.10.28

CAN Message Transfer

Once the CAN controller is initialized, the CAN controller synchronizes itself to the CAN bus and starts
transferring messages.
Received messages are stored to their appropriate message objects, if they pass the message handler's
acceptance filtering. The entire message, including all arbitration bits,
mask and control bits
object. Masked arbitration bits might change in the message object when a received message is stored.
The host processor may read or update each message at any time using the message interface registers. The
message handler guarantees data consistency when the host processor accesses the message object at the
same time the message is being transferred to or from RAM.
Messages to be transmitted are updated by the host processor. If a permanent message object (arbitration
and control bits set up during configuration are unchanged for multiple CAN transfers) exists for the
message, only the data bytes need to be updated. If several transmit messages are assigned to the same
message object (when the number of message objects is not sufficient)​, the whole message object has to be
configured before the transmission of this message is requested.
The transmission of any number of message objects may be requested at the same time they are
transmitted, according to their internal priority. The message object numbers are 1 to 128, with 1 being the
highest internal priority and 128 the lowest priority. Messages may be updated or set to invalid (
at anytime, even when their requested transmission is still pending. The old data is discarded when a
message is updated before its pending transmission has started.
Depending on the configuration on the message object, the transmission of a message may be requested
automatically by the reception of a remote frame with a matching identifier. Remote frames are frames
used to request a particular message on the CAN network.
Note: For ease in programming, Altera recommends using one
direction activity and the other
Message Object Reconfiguration for Frame Reception
To configure a message object to receive data frames, set the
To configure a message object to receive remote frames, set the
to 0.
To avoid modifying an object while it is being transmitted, you must set
of the following configuration and control bits:
•
ID[28:0]
•
Xtd
•
DLC[3:0]
•
RxIE
•
TxIE
•
RmtEn
•
EoB
•
UMask
•
Msk[28:0]
•
MXtd
•
MDir
CAN Controller
Send Feedback
, , , ,
UMask MXtd MDir EoB MsgLst
message interface for all transmit direction activity.
IF
CAN Message Transfer
, ,
Xtd Dir
, , , and , is stored in the message
RxIE TxIE RmtEn
message interface for all receive
IF
field to 0.
Dir
field to 1, set
Dir
MsgVal
25-13
, eight data bytes, the
DLC
=0)
MsgVal
to 1, and set
UMask RmtEn
to 0 before changing any
Altera Corporation