NXP Semiconductors PXN2020, Reference Manual, Page: 712 / 1376

FlexRay Communication Controller (FlexRAY)
PXN20 Microcontroller Reference Manual, Rev. 1
26-98 Freescale Semiconductor
Before an individual message buffer can be used, it must be configured by the application. After the initial
configuration, the message buffer can be reconfigured later. The set of the configuration data for individual
message buffers is given in
Section 26.6.3.4.1, Individual Message Buffer Configuration Data.
26.6.6.1 Individual Message Buffer Configuration
The individual message buffer configuration consists of two steps. The first step is the allocation of the
required amount of memory for the FlexRay memory. The second step is the programming of the message
buffer configuration registers, which is described in this section.
26.6.6.1.1 Common Configuration Data
One part of the message buffer configuration data is common to all individual message buffers and the
receive shadow buffers. These data can only be set when the protocol is in the
POC:config state.
The application configures the number of utilized individual message buffers by writing the message
buffer number of the last utilized message buffer into the LAST_MB_UTIL field in the
Message Buffer
Segment Size and Utilization Register (MBSSUTR) .
The application configures the size of the two segments of individual message buffers by writing the
message buffer number of the last message buffer in the first segment into the LAST_MB_SEG1 field in
the
Message Buffer Segment Size and Utilization Register (MBSSUTR)
The application configures the length of the message buffer data fields for both of the message buffer
segments by writing to the MBSEG2DS and MBSEG1DS fields in the
Message Buffer Data Size Register
(MBDSR) .
Depending on the current receive functionality of the controller, the application must configure the receive
shadow buffers. For each segment and for each channel with at least one individual receive message buffer
assigned, the application must configure the related receive shadow buffer using the
Receive Shadow
Buffer Index Register (RSBIR) .
26.6.6.1.2 Specific Configuration Data
The second part of the message buffer configuration data is specific for each message buffer.
These data can be changed only when either
• the protocol is in the POC:config state or
• the message buffer is disabled (MBCCSR n [EDS] = 0)
The individual message buffer type is defined by the MTD and MBT bits in the Message Buffer
Configuration, Control, Status Registers (MBCCSRn) as given in Table 26-94 .
Table 26-94. Individual Message Buffer Types
MBCCSRn[MTD] MBCCSRn[MBT] Individual Message Buffer Description
0 0 Receive Message Buffer
0 1 Reserved
1 0 Single Transmit Message Buffer
1 1 Double Transmit Message Buffer