NXP Semiconductors MPC5644A, Reference Manual, Page: 1534 / 1735

FlexRay Communication Controller (FlexRay)
MPC5644A Microcontroller Reference Manual, Rev. 6
1534 Freescale Semiconductor
Figure 33-114. Individual message buffer structure
33.6.3.1.1 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 (FR_MBSSUTR) . All individual message buffers
with a message buffer number n < FR_MBSSUTR[LAST_MB_SEG1] belong to the first message buffer
segment. All individual message buffers with a message buffer number
n > FR_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 * FR_MBDSR[MBSEG1DS] bytes
• the minimum length of the message buffer data field for individual message buffers assigned to the
second segment is 2 * FR_MBDSR[MBSEG2DS] bytes.
33.6.3.2 Receive shadow buffers
The receive shadow buffers are required for the frame reception process for individual message buffers.
The CC provides four receive shadow buffers, one receive shadow buffer per channel and per message
buffer segment.
Each receive shadow buffer consists of two parts, the physical message buffer located in the FlexRay
memory area and the receive shadow buffer control registers located in dedicated registers. The structure
of a receive shadow buffer is shown in
Figure 33-115 . The four internal shadow buffer control registers
can be accessed by the Receive Shadow Buffer Index Register (FR_RSBIR) .
The connection between the receive shadow buffer control register and the physical message buffer for the
selected receive shadow buffer is established by the receive shadow buffer index field RSBIDX in the
Receive Shadow Buffer Index Register (FR_RSBIR) . The start address SADR_MBHF of the related
message buffer header field in the FlexRay memory area is determined according to Equation 33-3 .
FR_MBFIDRn
Message Buffer Control Registers
FR_MBCCSRn FR_MBCCFRn FR_MBIDXRn
(min) FR_MBDSR[MBSEG1DS] * 2 bytes / FR_MBDSR[MBSEG2DS] * 2 bytes
Data Field Offset
Frame Data
Message Buffer Header Field
Message Buffer Data Field
Slot Status Frame Header
SADR_MBDF
SADR_MBHF
Fl
exRay Memory