NXP Semiconductors MPC5644A, Reference Manual, Page: 835 / 1735

Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 835
2. The Scheduler proceeds to time slot two, which has middle-level priority; however, no
middle-level channel is requesting service. Priority is passed to the high level, but no high-level
channel is requesting service; therefore, priority is passed again, and service is granted to the single
requesting low-level channel. Once serviced, this channel’s grant bit is negated (no more low-level
requests).
3. The Scheduler resumes with the fixed-priority sequence on time slot three; however, no channels
are requesting service. The Scheduler returns to time slot one, waiting for requests.
4. Two high-level and two middle-level channels simultaneously request service. Being in time slot
one which is assigned high priority, the Scheduler finds the lowest numbered high-level channel
(secondary scheme) and selects it for service. This channel’s service grant bit is asserted.
5. The Scheduler continues to time slot two, which has middle priority (primary scheme), and
allocates the slot to the lowest numbered middle-level channel requesting service (secondary
scheme). The Scheduler notes the still unserviced middle-level channel and proceeds to time slot
three.
6. Time slot three is allocated for high priority. The slot is allocated to the remaining unserviced
high-priority channel, and the channel’s service grant bit is asserted. The Scheduler checks again
at the end of the thread. All service grant bits of high-level requested channels are asserted;
therefore, all high-priority channels that requested have been allocated execution time. Under this
condition, all service grant bits of the high-level serviced channels are negated. The Scheduler
proceeds to time slot four.
7. Time slot four is allocated for low-priority channel; however, no low-level channel is requesting
service. Priority is passed to the high level, but no high-level channel is requesting service;
therefore, priority is passed again, and service is granted to the remaining middle-level channel
which requests service. This channel’s service grant bit is asserted. The Scheduler checks again at
the end of the thread. All grant bits of middle-level requested channels are asserted; therefore, all
middle-priority channels have been allocated execution time. Under this condition, all service grant
bits of the middle-level serviced channels are negated. The Scheduler proceeds to time slot five.
Meanwhile a low priority channel requests service.
8. Time slot five is allocated for high-priority channels, but there are no more requests from
high-priority or middle priority channels. The single low-level channel which required service is
granted time slot five. Once serviced, the channel’s service grant bit is asserted. Next, the service
grant bit is negated (no more requests of low priority level channels).
9. The Scheduler resumes with the fixed-priority sequence on time slot six; however, no channels are
requesting service. The Scheduler returns to time slot one and waits for requests.
24.5.3.3 Time Slot Latency
Latency is the amount of time between a service request and the beginning of service on that channel. The
following factors affect latency:
• Number of active channels
• Number of channels on a priority level
• Number of available time slots on a priority level
• Number of microcycles required to execute a thread of a Function