RM0029 Datasheet, PDF (1548/1740 Pages) STMicroelectronics – The primary objective of this document

FlexRay Communication Controller (FlexRay)
RM0029
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
SADR_MBHF
Frame Data
Message Buffer Data Field
Frame Header
Data Field Offset
Message Buffer Header Field
Slot Status
Figure 939. Physical message buffer structure
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 939. The physical start address SADR_MBHF of the message
buffer header field must be 16-bit aligned.
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 , Frame header description.
Data field offset
The data field offset follows the frame header in the message buffer data field and occupies
two bytes. It contains the offset of the corresponding message buffer data field with respect
to the CC FlexRay memory area base address as provided by SMBA field in the System
Memory Base Address Register (FR_SYMBADR). The data field offset is used to determine
the start address SADR_MBDF of the corresponding message buffer data field in the
FlexRay memory area according to Equation 44.
Equation 44 SADR_MBDF = [Data Field Offset] + SMBA
Slot status
The slot status occupies the last two bytes of the message buffer header field. It provides
the slot and frame status related information according to the FlexRay Communications
System Protocol Specification, Version 2.1 Rev A. A detailed description of the content and
usage of the slot status is provided in Section , Slot status description.
Message buffer data field
The message buffer data field is a contiguous area of 2-byte entities. This field contains the
frame payload data, or a part of it, of the frame to be transmitted to or received from the
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