Freescale Semiconductor FlexRay MFR4310 - Application Information; Shut down Sequence; Table 3-111. Minimum F Chi [Mhz] Examples (128 Message Buffers)

FlexRay Module (FLEXRAYV4)
MFR4310 Reference Manual, Rev. 2
204 Freescale Semiconductor
macroticks with a nominal duration of gdMacrotick. The minimum duration of a corrected macrotick is
gdMacrotick
min
equaling 39 µμT. This results in a minimum slot length of:
Eqn. 3-27
The search engine is located in the CHI and runs on the CHI clock. It evaluates one individual message
buffer per CHI 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 CHI clock cycles is required to ensure
correct operation. For a given number of message buffers and for a given CHI clock frequency f
chi
, this
results in a search duration of
Eqn. 3-28
The message buffer search must be finished within one slot which requires that Equation 3-29 must be
fulfilled
Eqn. 3-29
This results in the formula given in Equation 3-30 which determines the required minimum CHI frequency
for a given number of message buffers that are utilized.
Eqn. 3-30
The minimum CHI frequency for a selected set of relevant protocol parameters is given in Table 3-111.
3.7 Application Information
3.7.1 Shut Down Sequence
This section describes a safe shut down sequence to stop the FlexRay module gracefully. The main targets
of this sequence are
• do not send invalid data on the FlexRay bus
• do not corrupt FlexRay bus and do not disturb ongoing communication
• finish all ongoing reception
Firstly, the application must disable all message buffers by triggering the EDT trigger bit in the Message
Buffer Configuration, Control, Status Registers (MBCCSRn), until the EDS flag is cleared by the FlexRay
module. This ensures that no transmission is started by the FlexRay module. If all message buffers are
disabled, the application issues the HALT command to the PE using the Protocol Operation Control
Register (POCR). The PE then waits for the end of the communication cycle and goes into the POC:halt
Table 3-111. Minimum f
chi
[MHz] examples (128 message buffers)
pdMicrotick
[ns]
gdMinislot
234567
25.0 70.77 47.18 35.39 28.31 23.59 20.22
50.0 35.39 23.59 17.70 14.16 11.80 10.11
Δ
slotmin
39 pdMicrotick gdMinislot⋅⋅=
Δ
search
1
f
chi
--------
# MessageBuffers 10+()⋅=
Δ
search
Δ
slotmin
≤
f
chi
# MessageBuffers 10+
39 pdMicrotick gdMinislot⋅⋅
------------------------------------------------------------------------
≥