PXN20RM Datasheet, PDF (692/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

FlexRay Communication Controller (FlexRAY)
26.6 Functional Description
This section provides a detailed description of the functionality implemented in the controller.
26.6.1 Message Buffer Concept
The controller uses a data structure called message buffer to store frame data, configuration, control, and
status data. Each message buffer consists of two parts, the message buffer control data and the physical
message buffer. The message buffer control data are located in dedicated registers. The structure of the
message buffer control data depends on the message buffer type and is described in Section 26.6.3,
Message Buffer Types. The physical message buffer is located in the FlexRay memory and is described in
Section 26.6.2, Physical Message Buffer.
26.6.2 Physical Message Buffer
All FlexRay messages and related frame and slot status information of received frames and of frames to
be transmitted to the FlexRay bus are stored in data structures called physical message buffers. The
physical message buffers are located in the FlexRay memory.The structure of a physical message buffer is
depicted in Figure 26-103.
A physical message buffer consists of two fields, the message buffer header field and the message buffer
data field. The message buffer header field contains the frame header, the data field offset, and the slot
status.The message buffer data field contains the frame data.
The connection between the two fields is established by the data field offset.
SADR_MBDF
Frame Data
Message Buffer Data Field
SADR_MBHF
Frame Header
Data Field Offset
Slot Status
Message Buffer Header Field
Figure 26-103. Physical Message Buffer Structure
26.6.2.1 Message Buffer Header Field
The message buffer header field is a contiguous region in the FlexRay memory and occupies ten bytes. It
contains the frame header, the data field offset, and the slot status. Its structure is shown in Figure 26-103.
The physical start address SADR_MBHF of the message buffer header field must be 16-bit aligned.
26.6.2.1.1 Frame Header
The frame header occupies the first six bytes in the message buffer header field. It contains all FlexRay
frame header related information according to the FlexRay Communications System Protocol
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PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor