PXR40RM Datasheet, PDF (662/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

FlexRay Communication Controller (FLEXRAY)
Each individual message buffer consists of two parts, the physical message buffer, which is located in the
flexray memory, and the message buffer control data, which are located in dedicated registers. The
structure of an individual message buffer is given in Figure 22-104.
Each individual message buffer has a message buffer number n assigned, which determines the set of
message buffer control registers associated to this individual message buffer. The individual message
buffer with message buffer number n is controlled by the registers MBCCSRn, MBCCFRn, MBFIDRn,
and MBIDXRn.
The connection between the message buffer control registers and the physical message buffer is
established by the message buffer index field MBIDX in the Message Buffer Index Registers (MBIDXRn).
The start address SADR_MBHF of the related message buffer header field in the flexray memory is
determined according to Equation 22-3.
SADR_MBHF = (MBIDXRn[MBIDX] * 10) + SMBA
Eqn. 22-3
(min) MBDSR[MBSEG1DS] * 2 bytes / MBDSR[MBSEG2DS] * 2 bytes
SADR_MBDF
Frame Data
Message Buffer Data Field
SADR_MBHF
Frame Header
Data Field Offset
Slot Status
Message Buffer Header Field
MBCCSRn
MBCCFRn
MBFIDRn
MBIDXRn
Message Buffer Control Registers
Figure 22-104. Individual Message Buffer Structure
22.6.3.1.1 Individual Message Buffer Segments
The set of the individual message buffers can be split up into two message buffer segments using the
Message Buffer Segment Size and Utilization Register (MBSSUTR). All individual message buffers with
a message buffer number n <= MBSSUTR[LAST_MB_SEG1] belong to the first message buffer segment.
All individual message buffers with a message buffer number n > MBSSUTR[LAST_MB_SEG1] belong
to the second message buffer segment. The following rules apply to the length of the message buffer data
field:
• all physical message buffers associated to individual message buffers that belong to the same
message buffer segment must have message buffer data fields of the same length
• the minimum length of the message buffer data field for individual message buffers in the first
message buffer segment is 2 * MBDSR[MBSEG1DS] bytes
• the minimum length of the message buffer data field for individual message buffers assigned to the
second segment is 2 * MBDSR[MBSEG2DS] bytes.
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PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor