NXP Semiconductors MPC5644A, Reference Manual, Page: 832 / 1735

Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
832 Freescale Semiconductor
priority. In Figure 24-31 , time slot one has a high-level assignment; therefore, a high-level channel
requesting service is recognized first. However, if no high-level channel requests service, the Scheduler
recognizes a requesting middle-level channel. If this level has no request, the Scheduler continues to the
low-level. If no requests occur, the Scheduler truncates the seven state cycle and starts a new cycle at time
slot one, waiting for the first request. Granting service to a different-level channel is called priority passing.
The order of passing always gives the highest priority to the assigned level, and the second priority to the
higher of the remaining requesting priority levels as shown in
Table 24-39 .
When priority is passed to another level, that level is serviced and the fixed-priority-level sequence is
resumed with the next time slot.
Figure 24-32. Priority Passing Example
Examples of priority passing are shown in Figure 24-32 . Each cycle contains seven time slots (or less if
no service request exist). In cycle B, no high-level or middle-level service requests are present before time
slot three which is assigned by default to high-level priority. Thus, time slot three is passed to the low level.
In cycle B there are also no middle-level service requests before time slot six, so it passes the priority to a
requesting high-level channel. During time slot six no more high level requests are left, but two new
Table 24-39. Priority passing
Assigned
priority level
Next
priority level
Next
priority level
High

Middle

Low
Middle

High

Low
Low

High

Middle
SLOT Number
6 7 1 2 3 4 5 6 1 2 3 1
M H H M H L H M H H M H H
High Pend Count
Service High
2 1
0 1 0
2 0
- X New Service Requests Arrive at a Specific Priority Level
2 0
X
2
2 2
1
1
1 0
0 0 1
2
2
1 0 2
2
7
DH DM DH H>L DL DH M>H DM H>M H>M M>L H>L
1
0
DH, DH, DL - Default Service High, Middle or Low
H>L, H>M, M>H, M>L - Priority Passing Scheme
ID - Idle (no service request)
ID
Slot Assignment
SLOT ASSIGNMENTS:
Reset Slot
Fixed Priority Level
Middle Pend Count
Service Middle
Low Pend Count
Service Low
Number
Cycle A
Cycle B
Cycle C (truncated)
Cycle D
2 3
M H
1
1
1
1
0 1
1
0
0
1
H
H>M
DM DH
1
H
ID