FlexRay Communication Controller (FlexRAY)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 26-157
26.7.5.2 Behavior in Static Segment
In this case, both message buffers are assigned to a slot S in the static segment.
The configuration of a transmit buffer for a static slot S assigns this slot to the node as a transmit slot. The
FlexRay protocol requires:
• When a slot occurs, if the slot is assigned to a node on a channel that node must transmit either a
normal frame or a null frame on that channel. Specifically, a null frame will be sent if there is no
data ready, or if there is no match on a transmit filter (cycle counter filtering, for example).
Regardless of the availability of data and the cycle counter filter, the node will transmit a frame in the static
slot S. In any case, the result of the message buffer search will be the transmit message buffer t. The receive
message buffer r will not be found, no reception is possible.
26.7.5.3 Behavior in Dynamic Segment
In this case, both message buffers are assigned to a slot S in the dynamic segment. The FlexRay protocol
requires:
• When a slot occurs, if a slot is assigned to a node on a channel that node only transmits a frame on
that channel if there is data ready and there is a match on relevant transmit filters (no null frames
are sent).
The transmission of a frame in the dynamic segment is determined by the availability of data and the match
of the cycle counter filter of the transmit message buffer.
26.7.5.3.1 Transmit Data Not Available
If transmit data are not available, i.e.,the transmit buffer is not committed MBCCSRt[CMT] = 0 and/or
locked MBCCSRt[LCKS] = 1,
a) for the cycles in the set {4n}, which is assigned to both buffers, the receive buffer will be found
and the node can receive data, and
b) for the cycles in the set {4n + 2}, which is assigned to the receive buffer only, the receive buffer
will be found and the node can receive data.
The receive cycles are shown in Figure 26-153.
Figure 26-153. Transmit Data Not Available
26.7.5.3.2 Transmit Data Available
If transmit data are available, i.e.,the transmit buffer is committed MBCCSRt[CMT] = 1 and not locked
MBCCSRt[LCKS] = 0,
a) for the cycles in the set {4n}, which is assigned to both buffers, the transmit buffer will be found
and the node transmits data.
0
RX
1 2
RX
3 4
RX
5 6
RX
7 59 60
RX
61 62
RX
8
RX
63
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