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Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
907
Figure 24-60. High Rate Mode – Acceleration
24.5.7.6
Special cases of missing teeth and last tooth
The EAC handles cases of up to three missing teeth and the last tooth in the engine cycle. The following
paragraphs describe these functions.
24.5.7.6.1
Handling the last tooth
The microcode can set the TCR2 counter to work in engine periods (wrap-around count) or continuous
angle measurement.
For periodic operation, during the last engine cycle tooth the EAC microcode has to set the LAST flag in
TPR. As a result, when the tooth period is ended, the Counter Control Logic generates a reset command
to both the Tooth Tick Counter and TCR2 instead of an advance command. The operation resets the TCR2
based angle count, indicating a new period of the engine cycle. This implementation provides an engine
cycle based periodic angle measurement.
24.5.7.6.2
Handling missing teeth
The EAC can handle up to three missing teeth in two ways:
•
Count the angle ticks relative to the last physical tooth. The microcode should update the TPR
TICKS field to the number of angle ticks included in two, three or four teeth, according to the
flywheel type (one, two or three missing teeth). EAC hardware works in its regular manner.
•
Insert a “dummy” tooth instead of the missing tooth, at the estimated point in time. After the
“dummy” tooth, the Angle Tick Counter is incremented as if there was a physical tooth. A
“dummy” tooth can be inserted only during Normal or High Rate operation modes. The microcode
inserts “dummy” teeth by writing to the MISSCNT field in TPR.
Tooth Signal
Angle Tick
TRR
P1
P2
P3
P4
EAC Channel
Service Time Slot
EAC Channel
Capture
P1/ n
P2/ n
P3/ n
y
y+n+1
Ch0
Ch0
Ch0
High Rate Mode
TCR1
TCR1
TCR1
TCR1
*service request
**microcode updates TRR
*
*
**
**
TCR2
Tooth Tick Counter
Содержание MPC5644A
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