NXP Semiconductors MPC5644A, Reference Manual, Page: 972 / 1735

Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
972 Freescale Semiconductor
24.6.4.3 Changing channel function, parameter base, or entry table scheme
Channel Function, Parameter Base Address and Entry Table Scheme are determined by the ETPU_CxCR
fields CFS, CPBA and ETCS. They cannot be changed when the channel is enabled. If the channel is
disabled first, one may still have service requests from the previous function, so before the channel is
enabled again one must be sure that:
• The first thread executed in the new function is the initialization one.
• The initialization thread of the new function clears any previously pending service request.
Follows a safe procedure for function changing:
1. Disable the channel (write ETPU_CxCR field CPR = 00).
2. Change the function configuration (ETPU_CxCR fields CFS and/or CPBA and/or ETCS).
3. Request the initialization thread, writing ETPU_CxHSRR with the initialization HSR (channel still
disabled).
4. Enable the channel (write ETPU_CxCR field CPR > 0); the initialization HSR is serviced before
any other formerly pending service requests, clearing them.
24.6.4.4 Checking and clearing interrupts of a stopped engine
An engine may be stopped with interrupts (or DMA requests) pending. This includes the case when the
engine’s MDIS bit is set and a thread is still running: the thread will complete execution, possibly issuing
an interrupt or DMA request before the engine stops, setting the STF bit.
As soon as the engine stops the channel registers become inaccessible, issuing bus errors when accessed.
Interrupts and DMA requests can still be checked and cleared through the Global Channel Registers,
though. DMA requests can also be cleared by the hardware handshaking with the DMA controller when
the engine is stopped.
24.6.5 Estimating worst-case latency
Reliable systems are designed to work under worst-case conditions. This section explains how to estimate
worst-case latency (WCL) for any eTPU function in any system. The appendix covers the following topics:
• Introduction to Worst-Case Latency
• Using Worst-Case Latency Estimates to Evaluate Performance
• 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.