Cycle counter on ARM Cortex M4 (or M3)?

embedded arm cortex-m3
makapuf picture makapuf · Jul 17, 2012 · Viewed 32.2k times · Source

I'm trying to profile a C function (which is called from an interrupt, but I can extract it and profile it elsewhere) on a Cortex M4.

What are the possibilities to count the number of cycles typically used in this function ? Function shall run in ~4000 cycles top, so RTC isn't an option I guess, and manually counting cycles from disassembly can be painful - and only useful if averaged because I'd like to profile on a typical stream with typical flash / memory usage pattern.

I have heard about cycle counter registers and MRC instructions, but they seem to be available for A8/11. I haven't seen such instructions in cortex-Mx micros.

Answer

Throwback1986 picture Throwback1986 · Jul 17, 2012

Take a look at the DWT_CYCCNT register defined here. Note that this register is implementation-dependent. Who is the chip vendor? I know the STM32 implementation offers this set of registers.

This post provides instructions for using the DWT Cycle Counter Register for timing. (See the post form 11 December 2009 - 06:29 PM)

This Stack overflow post is an example on how to DWT_CYCCNT as well.

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