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Enhanced Time Processing Unit (eTPU2)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
911
2. Start a thread to reconfigure the EAC. The thread must set the EAC controlling channel (0, 1 or 2)
flags in a state, depending on the channel mode, that lets the channel tooth detection window open
(see
Section 24.5.7.10, Angle logic and channel modes
). It can optionally write TCR2 with an
angle preset value equivalent to the first tooth expected after restart. The thread must also set TPR
bit HOLD = 1. The TPR bit IPH must be 0.
3. After the thread is finished, write ETPU_TBCR setting AM = 01, 10 or 11, and TCR2CTL
according to the desired tooth edge selection if AM = 01.
The first tooth detected after this procedure restarts the TCR2 counting, unfreezing the Angle Mode logic
into normal mode.
24.5.7.12 Special TPR write cases
This section describes how simultaneous modification of TPR fields are resolved, and how the effect of
TPR writes depend on the EAC mode.
24.5.7.12.1
TPR buffering
Section 24.5.7.5.3, High rate mode (Acceleration)
), TPR writes are immediately
effective only for bits IPH and HOLD. Writes to all other fields are “buffered” and become effective when
EAC leaves High Rate mode. However, if TPR is written a second time right after IPH is asserted in
Normal mode, this second write behaves as if EAC is still in Normal mode. Only in the next microcycle
(after execution of a NOP, for instance) the TPR writes are buffered, acknowledging High Rate mode.
MISSCNT and LAST can be written any value during High Rate mode, and the value that prevails for the
next tooth is the one sampled when EAC goes back to Normal mode (or the value written in Normal or
Halt mode thereafter). If MISSCNT and/or LAST are not zero when High Rate mode begins, they are
sampled into the internal EAC logic and are effective while High Rate lasts (missing teeth count continues
and TCR2 is reset at the end of High Rate if LAST = 1). However, their values in TPR are reset when High
Rate mode starts. After that and until the end of High Rate mode, the value read by microcode is the same
written. This behavior prevents read-modify-writes to TPR from unwillingly rewriting LAST or
MISSCNT.
24.5.7.12.2
IPH and LAST
If both IPH and LAST are asserted in the same microinstruction, the EAC acts as if LAST was set first and
then IPH right after, so that:
•
In Normal mode, it goes to High Rate with LAST = 1;
•
In Halt mode, it goes to Normal Mode resetting LAST (and TCR2);
•
In High Rate mode, IPH is ignored and LAST becomes effective in the next tooth (physical or
inserted) after it goes back to Normal mode.
24.5.7.12.3
IPH and TICKS
Because of different results depending on the EAC mode at the time of TPR write, it is not advisable to
write 1 to IPH and change TICKS at the same microinstruction. A consistent behavior is obtained if IPH
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