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Setting CMPB = to CMPA even if in shadow mode?

Fulano de Tal
Expert 2090 points

If I have to do this

EPwm2Regs.CMPA.half.CMPA = (Uint16)(myValue * myValue2 / myValue 3);
EPwm2Regs.CMPB = (Uint16)(myValue * myValue2 / myValue 3);

Is it ok to do this instead?

EPwm2Regs.CMPA.half.CMPA = (Uint16)(myValue * myValue2 / myValue 3);
EPwm2Regs.CMPB = EPwm2Regs.CMPA.half.CMPA;

A and B are in shadow load mode.  Will CMPB have the right value?  Or will it have CMPA's old value?

  • 0
    TI__Guru 57255 points

    Fulano de Tal,

    Yes, the second option is alright.  The compiler will generate assembly code that accomplishes line 1 and then accomplishes line 2.  You can generally verify this by looking at the generated assembly code.

    There is one gotcha that should be known though (and it can hit you in either case).  You should run timing analysis to make sure that the shadow load point won't fall between your CMPA and CMPB write.  If it can, CMPA can be updated as the active value while CMPB waits until the next PWM cycle (assuming that this is a problem).


    Thank you,
    Brett