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19-4
MPC561/MPC563 Reference Manual
MOTOROLA
TPU Operation
request and assigns the channel to the microengine at the first available time. The
microengine performs the function defined by the content of the control store or emulation
RAM, using parameters from the parameter RAM.
19.3.1
Event Timing
Match and capture events are handled by independent channel hardware. This provides an
event accuracy of one time-base clock period, regardless of the number of channels that are
active. An event normally causes a channel to request service. The time needed to respond
to and service an event is determined by which channels and the number of channels
requesting service, the relative priorities of the channels requesting service, and the
microcode execution time of the active functions. Worst-case event service time (latency)
determines TPU3 performance in a given application. Latency can be closely estimated.
For more information, refer to the TPU Reference Manual (TPURM/AD).
19.3.2
Channel Orthogonality
Most timer systems are limited by the fixed number of functions assigned to each pin. All
TPU3 channels contain identical hardware and are functionally equivalent in operation, so
that any channel can be configured to perform any time function. Any function can operate
on the calling channel, and, under program control, on another channel determined by the
program or by a parameter. The user controls the combination of time functions.
19.3.3
Interchannel Communication
The autonomy of the TPU3 is enhanced by the ability of a channel to affect the operation
of one or more other channels without CPU intervention. Interchannel communication can
be accomplished by issuing a link service request to another channel, by controlling another
channel directly, or by accessing the parameter RAM of another channel.
19.3.4
Programmable Channel Service Priority
The TPU3 provides a programmable service priority level to each channel. Three priority
levels are available. When more than one channel of a given priority requests service at the
same time, arbitration is accomplished according to channel number. To prevent a single
high-priority channel from permanently blocking other functions, other service requests of
the same priority are performed in channel order after the lowest-numbered,
highest-priority channel is serviced (i.e. round-robin).
19.3.5
Coherency
For data to be coherent, all available portions of the data must be identical in age, or must
be logically related. As an example, consider a 32-bit counter value that is read and written