PXR40RM Datasheet, PDF (1255/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

Enhanced Time Processing Unit (eTPU2)
Note that PPWA function optimized for eTPU hardware can use double transition mode to measure
very narrow pulses with one service after the second transition, and latency will affect only the
minimum gap between two input pulses. Also the function threads would have more efficient
coding.
Finding the WCL for DIO on Channel 2
The following shows how to find the WCL for DIO on channel 2.
1. Find the worst-case service time for each active channel. See step 1 of previous examples.
2. Assume channel 2 has just been serviced and that channels 0 and 1 are continuously requesting
service. Using the H-M-H-L-H-M-H time-slot sequence, map the channels that are granted for
each time slot. See Figure 29-41.
WORST CASE LATENCY
CHANNEL 2
HM H LH MH HMH L H
= 10-CYCLE TIME SLOT TRANSITION
= 4-CYCLE NOP INSTRUCTION
CHANNEL 2 CHANNEL 1 CHANNEL 0 CHANNEL 0
SERVICED SERVICED SERVICED SERVICED
CHANNEL 0 CHANNEL 0 CHANNEL 1 CHANNEL 2
SERVICED SERVICED SERVICED SERVICED
Figure 29-41. Next Servicing for Channel 2
TPU CH2 WCL TIM
Channel 0 will be serviced four times and channel 1 twice before channel 2 is serviced again.
3. Add time for the ten-clock CPU time-slot transitions and the four-clock NOPs. See Figure 29-41
and Table 29-25.
Table 29-25. Worst Case Latency for Channel 2
Four Channel 0 worst-case service times 100 clocks
Two Channel 1 worst-case service time 92 clocks
Channel 2 worst-case service time
11 clocks
Seven 6-clock time-slot transitions
42 clocks
Total clocks
245 clocks
245 clocks * 25 ns/clock = 6125 ns
Conclusion: in this system configuration DIO can keep track of the input level at a minimum of
every 6125 ns.
Note that DIO function optimized for eTPU hardware can use double transition mode to measure
two pin transitions at a time and reduce the service time, improving the overall system performance
and latency.
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
29-87