Chapter 13 FlexRay Communication Controller (FLEXRAY)
MC9S12XF - Family Reference Manual, Rev.1.19
Freescale Semiconductor
583
If there are multiple message buffer with highest priority, the message buffer with the lowest message
buffer number is selected. All message buffer which have the highest priority must have a consistent
Depending on the message buffer channel assignment the same message buffer can be found for both
channel A and channel B. In this case, this message buffer is used as described in
Section 13.6.3.1,13.6.7.1
Message Buffer Cycle Counter Filtering
The message buffer cycle counter lter is a value-mask lter dened by the CCFE, CCFMSK, and
a set of communication cycles in which the message buffer is considered for message reception or message
transmission. If the cycle counter lter is disabled, i.e. CCFE = 0, this set of cycles consists of all
communication cycles.
If the cycle counter lter of a message buffer does not match a certain communication cycle number, this
message buffer is not considered for message transmission or reception in that communication cycle. In
case of a transmit message buffer assigned to a slot in the static segment, though, this buffer is added to
the matching message buffers to indicate the slot assignment and to trigger the null frame transmission.
The cycle counter lter of a message buffer matches the communication cycle with the number CYCCNT
if at least one of the following conditions evaluates to true:
Eqn. 13-9
Eqn. 13-10
13.6.7.2
Message Buffer Channel Assignment Consistency
transmit. The message buffer with number n transmits or receives on channel A if MBCCFRn[CHA] = 1
and transmits or receives on channel B if MBCCFRn[CHB] = 1.
To ensure correct message buffer operation, all message buffers assigned to the same slot and with the
same priority must have a consistent channel assignment. That means they must be either assigned to one
channel only, or must be assigned to both channels. The behavior of the message buffer search is not
Table 13-111. Message Buffer Search Priority (dynamic segment)
Priority
MTD
LCKS
CMT
CCFM
(1)
Description
Transition
(highest) 0
1011
transmit buffer, matches cycle count, not locked and committed
MA
1
0
n/a
1
receive buffer, matches cycle count, not locked
SB
(lowest) 2
0
1
n/a
1
receive buffer, matches cycle count, locked
SB
MBCCFRn CCFE
[]
0
=
CYCCNT MBCCFRn CCFMSK
[]
∧
MBCCFRn CCFVAL
[] MBCCFRn CCFMSK
[]
∧
=