Table of Contents
Advertisement
Enhanced Time Processing Unit (eTPU2)
At the beginning of High Rate mode operation, the TPR value is preloaded into a temporary register in the
Counter Control Logic, used for scanning all the valid values to the end of the current tooth, with its
appropriate LAST and MISSCNT attributes. While the EAC is in High Rate mode operation, the effect of
microcode update of TPR fields LAST, MISSCNT and TICKS is delayed to the next estimated tooth, after
1
the High Rate mode operation is complete
(see
Section 24.5.7.12, Special TPR write
cases). This is
because the current physical tooth represents the next estimated tooth. If the microcode updates this field
after High Rate mode operation is complete, the current physical tooth and estimated tooth are the same,
and the effect is immediate. Either in High-Rate mode or not, the value read by microengine is the same
written, even if not yet effective, until the EAC resets LAST and/or IPH, or decrements MISSCNT.
Typically the microcode service may occur during the High Rate mode on extreme acceleration situation
at low RPM. Therefore, the microcode operations are always related to the real physical tooth. From the
above it can be seen that the microcode updates of the TICKS field in TPR affect the end time of the current
physical tooth. For correct operation, this field should be updated before the Tooth Tick Counter has
reached either the old or the new TICKS value.
During High Rate mode operation, TRR is ignored and the Angle Tick Generator uses system clock
divided by eight. Therefore, the TRR update by microcode will take effect only after the EAC switches
back to Normal mode. If microcode service occurs after the Tooth Tick Counter has been reset, the EAC
is already back in Normal mode, and some angle ticks may have been counted at the rate of the previous
tooth. In this case the new TRR value will have immediate effect on the angle tick period, and the
microcode should take into consideration the delay from the physical tooth to the estimated tooth in
calculation of the next tooth period. See
Figure 24-60
for a detailed diagram of High Rate Mode behavior.
An angle error may be introduced by the duration of the High Rate mode. Also, the scheduler latency may
introduce a small accumulated error by using TRR value of the previous estimated tooth at the beginning
of the current tooth. After the estimated tooth has advanced, the duration of the High Rate mode operation
is the actual delay from the physical tooth edge to the estimated tooth edge. This delay can be obtained by
comparing the estimated tooth time with the EAC channel capture register which captured TCR1 on the
physical pin transition.
1. The effect of microcode writes to fields HOLD and IPH is immediate in High Rate mode.
MPC5644A Microcontroller Reference Manual, Rev. 6
906
Freescale Semiconductor
Advertisement
Table of Contents
