NXP Semiconductors MPC5644A, Reference Manual, Page: 909 / 1735

Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 909
Figure 24-61. Missing Teeth and Last Tooth Combination
24.5.7.7 Handling mechanical tooth correction
The EAC can handle tooth edge detection errors caused by flywheel mechanical errors. The eTPU
application can hold a vector of tooth mechanical errors with one entry per tooth. This error can be
measured in angle ticks which are independent of engine RPM. The TRR can be updated to the fixed
period of any tooth, including its mechanical error.
Because TCR2 counts continuously, without being reset, the mechanical correction is transparent. Though
the tooth has its own programmed TICKS value, TCR2 simply counts angle ticks, disregarding the
boundary between two adjacent teeth.
24.5.7.8 Handling mis-detected tooth
When a physical tooth signal is missed by the engine sensor, the EAC may get into Halt mode at the end
of the estimated tooth period, expecting the physical arrival. In this case, a Match timeout event of EAC
channel will call service which detects extreme deceleration. The microcode can assert the IPH bit in TPR,
to force the detection of the missed physical tooth. It can also calculate the accumulated angle bus error,
and fix the next estimated tooth period, to close the gap.
24.5.7.9 Handling false tooth detection
Most of the false tooth detection, caused by noises on the engine tooth sensor, can be eliminated by the
window blanking filtering, timed by EAC channel match recognitions. The EAC also provides means of
fixing false detection of an additional tooth which passed the window filter. When such an event occurs,
the EAC switched to High Rate mode (advancing to the next tooth) and when the next physical tooth
arrives, an extreme acceleration is detected: the EAC sees the remaining portion of the current tooth period
as another tooth period. The microcode can detect the situation when the acceleration in not realistic, or
when immediately after the detection of this extreme acceleration, the following tooth indicates extreme
deceleration back to the original RPM.
Tooth Signal
Angle Tick
TCR2
P1 P2 P3
P4
Tooth Tick Counter
EAC Channel
Service Time Slot
Tooth Count
Ch0
TPR[MISSCNT]
“Dummy Teeth”
TPR[LAST]
00 10 01 00
56 57 58 59 0
Dummy teeth
**microcode sets TPR
*service request
**
0
n*(TICKS+1)
(for reference only)