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f28335 floating point

James Quinn
Prodigy 50 points

I am trying to time the following code

GpioDataRegs.GPACLEAR.bit.GPIO31 = 1;
for (i=0; i<25; i++)
{
xdata *= 1.001;
}
GpioDataRegs.GPASET.bit.GPIO31 = 1;

It seems to take over 20 usec on a F28335 controlCARD (which is ridiculous).  Even though I believe I have hardware floating point selected in the compiler it still seems to be calling fs_mpy28() which looks like a software implementation.  For my project, to get it to compile I have to select Generic C28xx Device.  If I select Experimenter's Kit Defino F28335 or just F28335 I get all kinds of memory map errors.

  • 0
    Guru 192875 points
    Hi James,

    Which CCS version are you using? Secondly, you can check the Project -> Properties whether fpu32 is enabled or not. Go through all the menu items in properties.

    Regards,
    Gautam
  • 0 in reply to Gautam Iyer
    Prodigy 50 points
    Hi Gautam,
    CCS 6.0.1.00040
    fpu32 is checked.
    Why do I have to use Generic C28xx Device?
  • 0 in reply to James Quinn
    Guru 192875 points

    That's fine. Also, I would like you to check the timings using Profile Clock by using step into function during debugging.

  • 0 in reply to Gautam Iyer
    Prodigy 50 points
    I am not really using profiling. I am clearing and setting a GPIO and watching it on a scope. If I let optimization occur, the code runs faster but I cannot set a breakpoint on the multiply instruction, so I question whether the optimizer just got rid of the code since it doesn't actually do much. I suspect it has something to do with Properties-General-Main Generic C28xx Device?
  • 0
    Genius 3735 points

    Mr. Quinn,

    What CPU frequency are you running at?  20 usec would be 3000 instructions at 150 MHz (assuming zero wait states), or 120 instructions per iteration of your loop.  I would expect more like 6-8 cycles per loop iteration.  It should be very similar to the time required for integer multiplication.

    Regards,

    Bill

  • 0 in reply to Bill Finger
    Prodigy 50 points

    Bill,

    I am running at 150MHz.  When I put a breakpoint at the multiply and stepped into the operation it was very apparent that it was using the software routine instead of the FPU, even though I had fpu32 selected under processor options.  When I added --float_support=fpu32 under C2000 Compiler the execution time dropped to under 4 usec and the breakpoint shows a floating point instruction.  

    I cannot explain why it needs both, but under General if I try to use anything other than Generic C28xx Device, I get error complaining about memory section overlaps.  I am using a simple DOCK with a F28335 controlCARD.