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greg_t
greg_t
Associate III
September 23, 2010
Question

Instruction clocks

  • September 23, 2010
  • 2 replies
  • 688 views
Posted on September 23, 2010 at 17:18

Instruction clocks

    This topic has been closed for replies.

    2 replies

    lipin
    lipin
    Associate III
    May 17, 2011
    Posted on May 17, 2011 at 14:08

    clive1 is real expert in here. Anyway I will post some useful links about instructions and cyccnt:

    http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0337g/BABEACEG.html

    http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0337g/BABJFFGJ.html

    Regards

    Thomas

    Tesla DeLorean
    Tesla DeLorean
    Guru
    May 17, 2011
    Posted on May 17, 2011 at 14:08

    How many clocks needed for one instruction ?

    Depends : It's harder to do static analysis than in 1980, because there are far more complex interactions going on internally with a SoC design.

    It is usually one, but your execution speed is going to depend on how the flash prefetch works (because the flash is slow, probably ~30-35ns access time, and the buffering mechanism assumes linear code flow) whereas the ram is single cycle.

    Your load/store instructions are going to depend on the bus speed of the source/destination, be it multiple wait states on the flash, or slower peripheral buses. Or if others are using the bus.

    Want to benchmark code, uses the DWT_CYCCNT cycle counter in the trace/debug unit.

    Editing apparently alters the post ordering.

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