mfr4300 Freescale Semiconductor, Inc, mfr4300 Datasheet - Page 202

• Manufacturer Part Number: mfr4300
• Description: Flexray Communication Controllers
• Manufacturer: Freescale Semiconductor, Inc

FlexRay Module (FLEXRAYV2)
After this sequence, the FlexRay module is configured as a FlexRay node and is ready to be integrated into
the FlexRay cluster.
3.5.2
This section describes how to determine the number of message buffers that can be utilized at a given CHI
clock frequency f
The FlexRay module uses a sequential search to determine the individual message buffers suitable for
transmission or reception in the next slot. This search must be finished within one FlexRay slot. The
shortest FlexRay slot is an empty dynamic slot. An empty dynamic slot is a minislot and consists of at least
two macroticks. The minimum length of a corrected macrotick is 39 µT. The length of 1 µT is 25 ns. This
results in a minimum slot length of
The search engine is located in the CHI and runs on the CHI clock. The search engine searches one
individual message buffer per clock cycle. For internal status update and double buffer commit operations,
and as a result of the clock domain crossing jitter, an additional amount of 10 clock cycles is required to
ensure correct operation.
For a given number of message buffers and for a given CHI clock frequency f
duration of
As mentioned above, each message buffer search must be finished within one slot. Thus the following
equation must be fulfilled
This results in the formula to determine the minimum required CHI frequency for a given number of
message buffers that can be utilized.
The minimum CHI frequency for a selected set of message buffer numbers is given in
202
5. Start the FlexRay module as a FlexRay node
— configure the receive FIFOs
— write the READY protocol command into the POCCMD field of the
— now the FlexRay module enters the FlexRay protocol
Control Register (POCR)
Number of Usable Message Buffers
chi
.
Table 3-110. Minimum CHI Frequency Examples
t
slotmin
t
search
f
chi
=
=
# Message Buffers minimum f
t
1.95Ps
------- -
f
chi
1
MFR4300 Data Sheet, Rev. 3
-------------------------------------------------------- -
messagebuffers
t
search
˜
messagebuffers
32
=
d
1.95Ps
25
t
slotmin
------ - 39
PT
ns
˜
+
-------- - 2MT
MT
PT
10
21.54 MHz
+
˜
10
chi
chi
Protocol Operation
, this results in a search
Freescale Semiconductor
Table
3-110.
Eqn. 3-27
Eqn. 3-28
Eqn. 3-29
Eqn. 3-30