PXR40RM Datasheet, PDF (1248/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

Enhanced Time Processing Unit (eTPU2)
Time Slot Transitions
(10 CPU Clock Cycle Each)
HMH L HMH
Time Slots of
Varying Lengths
Figure 29-36. Time-Slot Sequence
This sequence scheme gives higher-priority channels more service time than lower-priority channels.
High-priority channels are allocated four of seven time slots, middle-priority channels are allocated two
of seven time slots, and low-priority channels are allocated one of seven time slots.
HMH L HMHHMH L HMHHMH
New 7-slot
Sequence
New 7-slot
Sequence
New 7-slot
Sequence
Figure 29-37. Multiple Time-Slot Sequences
29.4.2.3.1 Priority Passing
If no channel of the priority level assigned to the time slot is requesting service, the eTPU scheduler can
pass priority to other levels. If no high-level channel is requesting service during a high level time slot, a
middle-level channel is granted service; or, if no middle level-channel is requesting service, a low-level
channel is granted service. If no middle-level channel is requesting service during a middle-level time slot,
a high-level channel is granted service; or, if no high-level channel is requesting service, a low-level
channel is granted service. If no low-level channel is requesting service during a low-level time slot, a
high-level channel is granted service; or, if no high-level channel is requesting service, a middle-level
channel is granted service. If no channel is requesting service, the time slot sequence is reset to state 1 and
the scheduler idles until a request is received.
Priority passing is implemented in hardware and does not contribute to worst-case latency.
29.4.2.3.2 Time-Slot Transition
After each time slot, the eTPU must prepare for the next time slot. This preparation time between each
time slot is called a time-slot transition. See the eTPU Reference Manual for details. Time-slot transitions
can take from six up to ten eTPU clocks.
29-80
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor