PXR40RM Datasheet, PDF (1245/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

Enhanced Time Processing Unit (eTPU2)
• Priority Scheme Details used in WCL Analyses
• First-Pass WCL Analysis
• Second-Pass WCL Analysis
The first-pass WCL analysis is based on a deterministic, generalized formula that is easy to apply. Because
of the generalizations in the formula, the first analysis result is almost always much worse than the real
worst case. If the desired system performance is within the limits of this first analysis, then no further
analysis is required; the system is well within the performance limits of the eTPU. If the desired system
performance exceeds that indicated by the first analysis, the second-pass WCL analysis should be applied.
The second-pass analysis is not a generalized formula, but rather uses specific system details for a realistic
worst-case estimation.
29.4.2.1 Introduction to Worst-Case Latency
NOTE
In this Appendix the latency calculation and examples refer to old TPU
functions such as PWM, DIO etc. These functions use single action
channels which have single transition and single match functionality. They
are not optimized for the eTPU hardware enhancement which support
various double action modes. These examples are for reference only. New
eTPU functions which are optimized for the new hardware will impose
different latency calculations.
Worst-case latency for a channel is the longest amount of time that can elapse between the execution of
any two function threads on that channel. For example, if in a particular system, channel 5 is running
PWM, the worst-case latency for channel 5 is the longest possible time between the execution of two PWM
threads. The worst case time includes the time the execution unit takes to execute threads for other active
channels, and other delays described later in this section. Refer to Figure 29-34.
Worst Case Latency
for Channel 5
Additional Channel Threads
and other delays.
PWM Thread
executed for
Channel 5
Next PWM Thread
executed for
Channel 5
Figure 29-34. Worst-Case Latency for PWM
Worst-case latency for a channel depends both on the function running on that channel and on the activity
on other channels. Since the 32 eTPU channels must all share the same execution unit, execution speed of
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
29-77