Altera Embedded Peripherals IP - Manual (Page 301)

Performance Counter Core
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Core Overview
The performance counter core with Avalon ® interface enables relatively unobtrusive, real-time profiling
of software programs. With the performance counter, you can accurately measure execution time taken
by multiple sections of code. You need only add a single instruction at the beginning and end of each
section to be measured.
The main benefit of using the performance counter core is the accuracy of the profiling results. Alterna‐
tives include the following approaches:
• GNU profiler,
gprof
—
gprof
provides broad low-precision timing information about the entire
software system. It uses a substantial amount of RAM, and degrades the real-time performance. For
many embedded applications,
gprof
distorts real-time behavior too much to be useful.
• Interval timer peripheral—The interval timer is less intrusive than
gprof
. It can provide good results
for narrowly targeted sections of code.
The performance counter core is unobtrusive, requiring only a single instruction to start and stop
profiling, and no RAM. It is appropriate for high-precision measurements of narrowly targeted
sections of code.
For further discussion of all three profiling methods, refer to
AN 391: Profiling Nios II Systems .
The core is designed for use in Avalon-based processor systems, such as a Nios ® II processor system.
Altera ® device drivers enable the Nios II processor to use the performance counters.
Functional Description
The performance counter core is a set of counters which track clock cycles, timing multiple sections of
your software. You can start and stop these counters in your software, individually or as a group. You can
read cycle counts from hardware registers.
The core contains two counters for every section:
• Time: A 64-bit clock cycle counter.
• Events: A 32-bit event counter.
Section Counters
Each 64-bit time counter records the aggregate number of clock cycles spent in a section of code. The 32-
bit event counter records the number of times the section executes.
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