NXP Semiconductors PXN2020, Reference Manual, Page: 722 / 1376

FlexRay Communication Controller (FlexRAY)
PXN20 Microcontroller Reference Manual, Rev. 1
26-108 Freescale Semiconductor
To certain message buffer fields, both the application and the controller have access. To ensure data
consistency, a message buffer locking scheme is implemented that is used to control the access to the data,
control, and status bits of a message buffer. The access regions for receive message buffers are depicted in
Figure 26-127 . A description of the regions is given in Table 26-100 . If an region is active as indicated in
Table 26-101 , the access scheme given for that region applies to the message buffer.
Figure 26-127. Receive Message Buffer Access Regions
The trigger bits MBCCSR n [EDT] and MBCCSR n [LCKT] and the interrupt enable bit MBCCSR n [MBIE]
are not under access control and can be accessed from the application at any time. The status bits
MBCCSR
n [EDS] and MBCCSR n [LCKS] are not under access control and can be accessed from the
controller at any time.
The interrupt flag MBCCSR n [MBIF] is not under access control and can be accessed from the application
and the controller at any time. controller set access has higher priority.
The controller restricts its access to the regions depending on the current state of the message buffer. The
application must adhere to these restrictions in order to ensure data consistency. The receive message
buffer states are given in
Figure 26-128 . A description of the message buffer states is given in Table 26-96 ,
which also provides the access scheme for the access regions.
The status bits MBCCSR n [EDS] and MBCCSR n [LCKS] provide the application with the required status
information. The internal status information is not visible to the application.
Table 26-100. Receive Message Buffer Access Region Description
Region
Access from
Region used for
Application Module
CFG read/write — Message Buffer Configuration, Message Data and Status Access
MSG read/write — Message Data, Header, and Status Access
RX — write-only Message Reception and Status Update
SR — read-only Message Buffer Search Data
Message Buffer Data Field: DATA[0-N]
Message Buffer Header Field: Frame Header
MBCCSRn[DVAL/DUP]
Message Buffer Header Field: Slot Status
Message Buffer Header Field: Data Field Offset
MBCCFRn[CHA/CHB/CCF*]
MBFIDRn[FID]
MBIDXRn[MBIDX]
MBCCSRn[MTD]
RX
SR
CFG
MSG