MPC555
/
MPC556
TIME PROCESSOR UNIT 3
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
17-3
17.2.5 Host Interface
The host interface registers allow communication between the CPU and the TPU3,
both before and during execution of a time function. The registers are accessible from
the IMB through the TPU3 bus interface unit. Refer to
for
register bit/field definitions and address mapping.
17.2.6 Parameter RAM
Parameter RAM occupies 256 bytes at the top of the system address map. Channel
parameters are organized as 128 16-bit words. Channels zero through 15 each have
eight parameters. The parameter RAM address map in
shows how parameter words are organized in memory.
The CPU specifies function parameters by writing to the appropriate RAM address.
The TPU3 reads the RAM to determine channel operation. The TPU3 can also store
information to be read by the CPU in the parameter RAM. Detailed descriptions of the
parameters required by each time function are beyond the scope of this manual. Refer
to the
TPU Reference Manual
(TPURM/AD)
and the Motorola
TPU Literature Pack-
age (TPULITPAK/D)
for more information.
17.3 TPU Operation
All TPU3 functions are related to one of the two 16-bit time bases. Functions are syn-
thesized by combining sequences of match events and capture events. Because the
primitives are implemented in hardware, the TPU3 can determine precisely when a
match or capture event occurs, and respond rapidly. An event register for each chan-
nel provides for simultaneous match/capture event occurrences on all channels.
When a match or input capture event requiring service occurs, the affected channel
generates a service request to the scheduler. The scheduler determines the priority of
the 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 emu-
lation RAM, using parameters from the parameter RAM.
17.3.1 Event Timing
Match and capture events are handled by independent channel hardware. This pro-
vides 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 re-
questing service, and the microcode execution time of the active functions. Worst-
case event service time (latency) determines TPU3 performance in a given applica-
tion. Latency can be closely estimated. For more information, refer to the
TPU Refer-
ence Manual
(TPURM/AD)
.
17.3.2 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 oper-
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Freescale Semiconductor, Inc.
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