Samsung S5PC100 User Manual page 701

CCAN
The initialization of the Message Objects is independent of Init and is done on the fly, but the Message Objects
should be configured to particular identifiers or set to not valid before the BSP starts the message transfer.
To change the configuration of a Message Object during normal operation, the CPU has to start by setting MsgVal
to not valid. If the configuration is completed, MsgVal is set to valid again.
4.1.1 CAN Message Transfer
Once the C_CAN is initialized and Init is reset to 0, the C_CAN's CAN Core synchronizes itself to the CAN bus
and starts the message transfer.
Received messages are stored into their appropriate Message Objects if they pass the Message Handler's
acceptance filtering. The whole message including all arbitration bits, DLC and eight data bytes is stored into the
Message Object. If the Identifier Mask is used, the arbitration bits which are masked to "don't care" may be
overwritten in the Message Object.
The CPU may read or write each message any time via the Interface Registers, the Message Handler guarantees
data consistency in case of concurrent accesses.
Messages to be transmitted are updated by the CPU. If a permanent Message Object (arbitration and control bits
set up during configuration) exists for the message, only the data bytes are updated and then TxRqst bit with
NewDat bit are set to start the transmission. If several transmit messages are assigned to the same Message
Object (If 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
subsequently according to their internal priority. Messages is updated or set to not valid any time, even if their
requested transmission is still pending. The old data is discarded if a message is updated before its pending
transmission has started.
Depending on the configuration of the Message Object, the transmission of a message may be requested
autonomously by the reception of a remote frame with a matching identifier.
4.1.2 Disabled Automatic retransmission
According to the CAN Specification (see ISO11898, 6.3.3 Recovery Management), the C_CAN provides means
for automatic retransmission of frames that have lost arbitration or that have been disturbed by errors during
transmission. The frame transmission service will not be confirmed to the user before the transmission is
successfully completed. By default, this means for automatic retransmission is enabled. It can be disabled to
enable the C_CAN to work within a Time Triggered CAN (TTCAN, see ISO11898-1) environment.
The Disabled Automatic Retransmission mode is enabled by programming bit DAR in the CAN Control Register to
one. In this operation mode the programmer has to consider the different behavior of bits TxRqst and NewDat in
the Control Registers of the Message Buffers:
•
If a transmission starts bit TxRqst of the respective Message Buffer is reset, while bit NewDat remains set.
•
If the transmission completed successfully bit NewDat is reset. If a transmission failed (lost arbitration or
error) bit NewDat remains set. To restart the transmission the CPU has to set TxRqst back to one.
8. 5-4
S5PC100 USER'S MANUAL (REV1.0)