NXP Semiconductors MPC5644A, Reference Manual, Page: 974 / 1735

Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
974 Freescale Semiconductor
independent. This means that, for example, all 32 channel signals can change thread at the same moment,
provided that the function software sets up the channel hardware to do so beforehand.
With Host CPU code, the system designer assigns functions to channels and initializes the functions. After
initialization, functions typically run without Host intervention, except for eTPU channel interrupts to the
Host to give or receive information. Most functions can run continuously with periodic servicing from the
eTPU Microengine. As required, the channels request service from the eTPU Microengine, and the eTPU
Scheduler determines the order in which the channels are serviced. Worst-case latency for a channel can
be derived from the details of the priority scheme that the scheduler uses (see
Section 24.5.3, Scheduler ).
Figure 24-65. Function threads
24.6.5.2 Using worst-case latency estimates to evaluate performance
Once WCL is found for a channel, the user must determine how to use this number to analyze performance.
To analyze the performance of a channel running the PWM function, for example, some information about
what happens in each thread is necessary.
The following example refers to old TPU PWM function, which is not optimized to the eTPU enhanced
hardware. For PWM, thread 1 is the initialization thread, and threads 2 and 3 are used during normal
function execution. (PWM threads 4, 5, and 6 are for special modes and will be assumed to be unused on
channel 5). Thread 2 writes a time into the channel 5 match register and performs other operations that will
cause the channel 5 signal to go from low to high at the time indicated in the match register (match time).
At match time, the signal goes high and channel 5 requests service from the eTPU Microengine to execute
thread 3. Thread 3 writes a time into the channel 5 match register and performs other operations that will
cause the channel 5 signal to go from high to low at match time. At match time, the signal goes low and
channel 5 requests service from the eTPU Microengine to execute thread 2. A PWM wave is kept running
on the system by the eTPU executing thread 2, then thread 3, then thread 2, then thread 3, and so on.
DIO Function Threads PWM Function Threads
SM Function Threads
S1
S2 S3 S4
S5 S6
S1
S2 S3 S4
S5 S6
S1
S2 S3 S4