EP80579 Datasheet, PDF (1582/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
39.5.3.3
39.5.3.4
Note:
Rx Message Processing
After receipt of a new message, the RxMessageHandler searches all receive buffers
starting from RxMessage0 until it finds a valid buffer.
A valid buffer is indicated by:
• Receive buffer is enabled indicated by RxBufferEbl = ‘1’.
• Acceptance Filter of receive buffer matches incoming message.
If the RxMessageHandler finds a valid buffer that is empty, then the message is stored
and the MsgAv flag is set to ‘1’. If the RxIntEbl flag is set, then the RxMsg flag of the
interrupt controller is set. If the receive buffer already contains a message indicated by
MsgAv = ‘1’ and the Link Flag is not set, then a RxMsgLoss interrupt flag is set.
If an incoming message has its RTR flag set and the RTRreply flag is set, then the
message is not stored but an RTR auto-reply is issued. See “Offset 000000A0h:
RxMessageControl[0-15] - Receive Message Command and Control” for more details.
Acceptance Filter
Each receive buffer has its own acceptance filter that is used to filter incoming
messages. An acceptance filter consists of an Acceptance Mask Register (AMR) and
Acceptance Code Register (ACR) pair. The AMR defines which bits of the incoming CAN
message have to match the respective ACR bits.
The following message fields are covered:
• ID
• IDE
• RTR
• Data byte 1 and data byte 2 (DATA[63:56])
Some CAN High Level Protocols such as SDS or Device Net carry additional protocol
related information in the first or first two data bytes that are used for message
acceptance and selection. The capability to filter on these fields provides a more
efficient implementation of the protocol stack running on the CPU.
The acceptance mask register (AMR) defines whether the incoming bit is checked
against the acceptance code register (ACR).
• AMR:
— ‘0’: The incoming bit is checked against the respective ACR. The message is not
accepted when the incoming bit doesn’t match the respective ACR flag.
— ‘1’: The incoming bit is ‘don’t care’.
Example:
The following example shows the acceptance register settings used to support receipt
of a CANopen TPD01 (Transmit Process Data Object) message. In CANopen, a widely
used CAN Higher Level Protocol (HLP), the ID bits are used to select the message type.
The bit assignment is shown in the following table:
Intel^® EP80579 Integrated Processor Product Line Datasheet
1582
August 2009
Order Number: 320066-003US