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Enhanced Time Processing Unit (eTPU2)
Each I/O signal pair is associated with a dedicated Channel, which provides hardware for input signal
processing and output signal generation, in relationship with selected Time Bases.
The eTPU, as a microprocessed subsystem, works much like a typical real-time system: it runs
microengine code from instruction memory (SCM) to handle specific events, accessing data memory
(SPRAM) for parameters, work data and application state info; events may originate from I/O Channels
(due to pin transitions and/or time base matches), Host CPU requests or inter-channel requests; events that
call for local eTPU processing activate the microengine by issuing a Service Request. The Service
Request microcode may set an interrupt to the Host CPU. I/O channel events cannot directly interrupt the
Host CPU.
Each channel is associated with a Function, which defines its behavior: the Function is a software entity
consisting, within the eTPU, of a set of microengine routines that attend to Service Requests. The Function
routines are also responsible for Channel configuration. Function routines reside in SCM, which may
contain several Functions. A Function may be assigned to several Channels, but a Channel can be
associated with just one Function at a given moment. The association between Functions and Channels is
defined by Host CPU, and is explained in detail in
eTPU hardware supplies resource sharing features that support concurrency:
•
a hardware Scheduler dispatches the Service Request microengine routines based on a set of
priorities defined by the Host CPU. Each Channel has its associated priority;
•
a Service Request routine cannot be interrupted until it ends. This sequence of uninterrupted
instruction execution is called a Thread.
•
Channel-specific context (registers and flags) is automatically switched between the end of a
Thread and the beginning of the next one.
•
SPRAM arbitration, a dual-parameter coherency controller and semaphores can be used to ensure
coherent access to eTPU data shared by both eTPU engines and Host CPU.
24.2.1.1
eTPU engine
The eTPU engine consists of two 24-bit time bases, 32 independent timer channels, a task scheduler, a
microengine, and a Host interface and 32-bit Shared Parameter RAM (SPRAM). In dual-engine
implementations of the eTPU, SPRAM is used for both eTPU engine's data storage and for passing
information between the eTPU engines and the host CPU.
Figure 24-2
shows the block diagram for the eTPU engine.
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Section 24.5.1, Functions and
MPC5644A Microcontroller Reference Manual, Rev. 6
threads.
Freescale Semiconductor
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