NXP Semiconductors MPC5644A, Reference Manual, Page: 894 / 1735

Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
894 Freescale Semiconductor
combines hardware with microcode processing at channel 0, 1 or 2. The angle measurement is based on
history knowledge of the tooth period, for predicting the period of the next tooth. The tooth period is
partitioned into a programmable number of
Angle Ticks . The eTPU application will use the divider in the
MAC/Divide unit to calculate an integer and a fraction part of the angle tick such that the full tooth period
gets the correct programmed number of angle ticks with no accumulated error.
Each single tooth can be divided in angle ticks, up to 1024. In a 60-tooth flywheel, 128 Angle Ticks per
tooth provide resolution of ~0.05 degrees per tick, which meets the accuracy requirement of 0.1 degrees
in current automotive applications.
The measurement of one tooth in angle ticks is independent on engine RPM; it is the tooth period itself
(and the corresponding tick period) that is re-calculated for each new tooth, based on the difference
between the estimated tooth and the actual detection.
For these applications, one of the eTPU channels 0, 1 or 2 is dedicated to service the physical tooth
detection. Channel 0 shares the same filtered input as the TCRCLK signal to get the same timing as the
EAC. The TCRCLK edge detection is selected by ETPU_TBCR field TCR2CTL for the EAC, and by
IPACA/B on channel 0, which must be set to detect the same edge(s). When channels 1 or 2 are selected
to work with the EAC, IPACA/B is used to select the tooth signal edge detection for both the channel and
the EAC, and the tooth signal that feeds the EAC is the same filtered input which feeds the channel.
Channel 0, 1 or 2 generates the signal transition service request, and can also be used for generation of a
window filter on this transition, to qualify TCR2 clocks. For this purpose, the selected channel should be
configured with double match window filtering mode (refer to
Section 24.5.5.4, Channel Modes ).
Depending on the channel mode set for the channel, Match A recognition opens the window, and Match
B recognition may close it or leave it open. See
Section 24.5.7.10, Angle logic and channel modes , for
details. Match B also generates a time-out service request. Its input signal transition comes from the tooth.
The window can be defined by microcode to open at a predefined point inside the tooth period, and stay
open for a desired percentage to the tooth period. The window can be measured in angle or time This
method improves the noise immunity by allowing transition detection only on an expected period, a feature
which was software responsibility in previous TPU versions.
The EAC supports deceleration, acceleration, last tooth and missing tooth scenarios. The large range of
angle ticks per tooth can be used to cover longer tick counts caused by one or more missing teeth, or to
provide extra resolution for future application requirements. In case of a missing tooth, the EAC can be
configured to insert a dummy tooth or to simply measure a longer tooth.
Figure 24-56 shows the block diagram of the Angle Counter system. TCR1 is used as a time base which
measures the tooth period and is used for partitioning the period to angle ticks.
24.5.7.2 Angle mode registers
In Angle Mode, the registers described below control eTPU angle operations. They are accessible only by
microengine as source and destination registers in microinstructions. When eTPU is not in angle mode
(AM bit is negated in ETPU_TBCR), all angle mode registers can be used as general purpose registers.