Texas Instruments TMS320 Series, User Manual

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Timers, Interrupts, and the System Clock
Thread Scheduling 4-71
4.9 Timers, Interrupts, and the System Clock
DSPs typically have one or more on-device timers which generate a
hardware interrupt at periodic intervals. DSP/BIOS normally uses one of the
available on-device timers as the source for its own system clock. Using the
on-device timer hardware present on most TMS320 DSPs, the CLK module
supports time resolutions close to the single instruction cycle.
You define the system clock parameters in the DSP/BIOS configuration
settings. In addition to the DSP/BIOS system clock, you can set up additional
clock objects for invoking functions each time a timer interrupt occurs.
On the C6000 platform, you can also define parameters for the CLK module’s
HWI object, since that object is pre-configured to use the HWI dispatcher.
This allows you to manipulate the interrupt mask and cache control mask
properties of the CLK ISR.
DSP/BIOS provides two separate timing methods—the high- and low-
resolution times and the system clock. In the default configuration, the low-
resolution time and the system clock are the same. However, your program
can drive the system clock using some other event, such as the availability of
data. You can disable or enable the CLK Manager’s use of the on-device
timer to drive high- and low-resolution times. You can drive the system clock
using the low-resolution time, some other event, or not at all. The interactions
between these two timing methods are shown in Example 4-16.
Figure 4-16. Interactions Between Two Timing Methods
Default configuration:
Low-resolution time and
system clock are the same
Low-resolution time
and system clock
are different
Only low- and high-
resolution times available;
timeouts don't elapse
Only system clock
available; CLK functions
don't run
No timing method;
CLK functions don't run;
timeouts don't elapse
Not possible
CLK module drives
system clock
CLK manager
enabled
CLK manager
disabled
Other event drives
system clock
No event drives
system clock