TIME PROCESSOR UNIT
MC68332
7-4
USER’S MANUAL
event service time (latency) determines TPU performance in a given application. La-
tency can be closely estimated — refer to Freescale
TPU Reference Manual (TPURM/
AD) for more information.
7.3.2 Channel Orthogonality
Most timer systems are limited by the fixed number of functions assigned to each pin.
All TPU channels contain identical hardware and are functionally equivalent in opera-
tion, 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.
7.3.3 Interchannel Communication
The autonomy of the TPU is enhanced by the ability of a channel to affect the opera-
tion of one or more other channels without CPU intervention. Interchannel communi-
cation 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.
7.3.4 Programmable Channel Service Priority
The TPU provides a programmable service priority level to each channel. Three prior-
ity levels are available. When more than one channel of a given priority requests ser-
vice 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.
7.3.5 Coherency
For data to be coherent, all available portions of it must be identical in age, or must be
logically related. As an example, consider a 32-bit counter value that is read and writ-
ten as two 16-bit words. The 32-bit value is read-coherent only if both 16-bit portions
are updated at the same time, and write-coherent only if both portions take effect at
the same time. Parameter RAM hardware supports coherent access of two adjacent
16-bit parameters. The host CPU must use a long-word operation to guarantee coher-
ency.
7.3.6 Emulation Support
Although factory-programmed time functions can perform a wide variety of control
tasks, they may not be ideal for all applications. The TPU provides emulation capability
that allows the user to develop new time functions. Emulation mode is entered by set-
ting the EMU bit in the TPUMCR. In emulation mode, an auxiliary bus connection is
made between TPURAM and the TPU module, and access to TPURAM via the inter-
module bus is disabled. A 9-bit address bus, a 32-bit data bus, and control lines trans-
fer information between the modules. To ensure exact emulation, RAM module access
timing remains consistent with access timing of the TPU ROM control store.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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