PXS20RM Datasheet, PDF (806/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

FlexRay Communication Controller
26.6.1 Message Buffer Concept
The CC 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 area 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 area.The structure of a physical message
buffer is depicted in Figure 26-113.
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 26-113. 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 area and occupies ten bytes.
It contains the frame header, the data field offset, and the slot status. Its structure is shown in
Figure 26-113. 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
Specification, Version 2.1 Rev A. A detailed description of the usage and the content of the frame header
is provided in Section 26.6.5.2.1, Frame Header Description.
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PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor