Freescale Semiconductor FlexRay MFR4310 - Clock Domain Crossing; Initialization Information; Lower Flexray Bit Rate Support; Table 3-110. Flexray Channel Bit Rate Control

FlexRay Module (FLEXRAYV4)
MFR4310 Reference Manual, Rev. 2
202 Freescale Semiconductor
3.4.20 Clock Domain Crossing
The Clock Domain Crossing module CDC implements the signal crossing from the CHI clock domain to
the PE clock domain and vice versa. The signal crossing logic is implemented as a three-stage pipe-line.
Two pipe-line stages are used for clock synchronization; the third stage is used for pulse generation.
3.4.20.1 Clock Domain Crossing Signal Latency
Due to the clock domain crossing implementation, each signal from the PE to the CHI is delayed by at least
two CHI clock cycles and by at most three CHI clock cycles. In terms of time, the signal latency time t
lat
for a given CHI frequency f
chi
is
Eqn. 3-26
3.5 Lower FlexRay Bit Rate Support
The FlexRay module supports a number of lower bit rates on the FlexRay bus channels. The lower bit rates
are implemented by modifying the duration of the microtick pdMicrotick, the number of samples per
microtick pSamplesPerMicrotick, the number of samples per bit cSamplesPerBit, and the strobe offset
cStrobeOffset. The application configures the FlexRay channel bit rate by setting the BITRATE field in the
Module Configuration Register (MCR). The protocol values are set internally. The available bit rates, the
related BITRATE field configuration settings and related protocol parameter values are shown in
Table 3-110.
NOTE
The bit rate of 8 Mbit/s is not defined by the FlexRay Communications
System Protocol Specification, Version 2.1 Rev A.
3.6 Initialization Information
This section provides information for initializing and using the FlexRay module.
Table 3-110. FlexRay Channel Bit Rate Control
FlexRay Channel
Bit Rate
[Mbit/s]
MCR.BITRATE
pdMicrotick
[ns]
gdSampleClockPeriod
[ns]
pSamplesPerMicrotick
cSamplesPerBit
cStrobeOffset
10.0 000 25.0 12.5 2 8 5
8.0 011 25.0 12.5 2 10 6
5.0 001 25.0 25.0 1 8 5
2.5 010 50.0 50.0 1 8 5
2
f
chi
--------
t
lat
3
f
chi
--------
≤≤