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Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
978
Freescale Semiconductor
the percentage of time it accesses the eTPU parameter RAM with or without using the CDC. This
percentage gives a good RCR and CPCR. The eTPU application provides a good estimation of CCR.
NOTE
The programming practice of polling a flag in the eTPU SPRAM causes a
very high RCR and should be avoided in high-performance systems.
After the collision rate for a system is found, it can be applied to the WCL calculations for each channel.
The system designer can use the collision percentage and the number of SPRAM accesses (with and
without semaphores) to estimate the eTPU loop time for a function. Note that in old TPU functions CPCR
and CCR are both zero.
The estimation of eTPU wait time is as follows:
Variables:
N1 = Number of simple RAM accesses in the longest thread
RCRWait = Maximal system clocks wait time for simple RAM collision = 2
CPCRWait = Average System Clocks for Coherent Parameter Transfer (using CDC).
N2 = Number of eTPU-eTPU semaphore RAM accesses in the longest thread
CCRWait = Average System Clocks for Microengine-Microengine communication transfer.
Estimated Wait Time:
Function eTPU maximal wait time =
N1 * (RCR * R CPCR * CPCRWait) + N2 * CCR * CCRWait
24.6.5.4
First-pass worst-case latency analysis
Following is the first-pass calculation of worst-case latency for a channel. Remember that this analysis
uses generalizations that usually produce a result much worse than the real worst case. If the worst-case
result from the first analysis is too long for the desired performance, use the second analysis for a more
realistic worst-case analysis.
24.6.5.4.1
Worst-case assumptions and formula
To estimate worst-case latency for a channel, assume this worst-case condition: the channel has just been
serviced in a time slot of its priority level, and all other channels in the system are continuously requesting
service and have cleared SGRs. The worst-case latency is the time from the end of the channel’s service
until the end of the channel’s next service. See
.
Summary of Contents for MPC5644A
Page 2: ...MPC5644A Microcontroller Reference Manual Rev 6 2 Freescale Semiconductor...
Page 24: ...MPC5644A Microcontroller Reference Manual Rev 6 24 Freescale Semiconductor...
Page 26: ...MPC5644A Microcontroller Reference Manual Rev 6 26 Freescale Semiconductor...
Page 52: ...Introduction MPC5644A Microcontroller Reference Manual Rev 6 52 Freescale Semiconductor...
Page 56: ...Memory Map MPC5644A Microcontroller Reference Manual Rev 6 56 Freescale Semiconductor...
Page 1228: ...Decimation Filter MPC5644A Microcontroller Reference Manual Rev 6 1228 Freescale Semiconductor...
Page 1440: ...FlexCAN Module MPC5644A Microcontroller Reference Manual Rev 6 1440 Freescale Semiconductor...