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ePWM Action Qualifier Control Register For Output Shadow registers

oyvind.skutlaberg
Prodigy 30 points

I'm running an application on a F28377S. If I enable shadowing of the ePWM AQCTLA/B registers it seems like the active registers are sometimes not loaded correctly. I set up the shadowing the following way:

    EPwm7Regs.AQCTL.bit.SHDWAQAMODE = 1;    // Shadow mode - operates as a double buffer. All writes via the CPU access Shadow register.
    EPwm7Regs.AQCTL.bit.SHDWAQBMODE = 1;    // Shadow mode - operates as a double buffer. All writes via the CPU access Shadow register.
    EPwm7Regs.AQCTL.bit.LDAQASYNC = 0;        // Shadow to Active Load of AQCTLA occurs according to LDAQAMODE
    EPwm7Regs.AQCTL.bit.LDAQBSYNC = 0;        // Shadow to Active Load of AQCTLA occurs according to LDAQBMODE
    EPwm7Regs.AQCTL.bit.LDAQAMODE = 0;        // Load on CTR = Zero
    EPwm7Regs.AQCTL.bit.LDAQBMODE = 0;        // Load on CTR = Zero

Reading the AQCTLA/B registers with JTAG shows correct values in the registers, however my PWM outputs are flat.


I also have shadowing enabled on TBPRD/CMPA/CMPB registers, loading on zero crossing. These are working correctly all the time.


My workaround is to load AQCTLA/B on SYNC (AQCTL.bit.LDAQASYNC=2). Any idea about why loading on ZRO (AQCTL.bit.LDAQASYNC=0) only works randomly?

  • 0
    TI__Mastermind 27200 points

    Oyvind,

    There is a note in the user's guide about possible contention if an AQ register update happens at the same time as an AQ edge.  Take a look at p.1595 of the User's Guide:

    http://www.ti.com/lit/ug/spruhm8e/spruhm8e.pdf

    If CMPA or CMPB are zero this might happen.  Could this be the problem?

    Regards,

    Richard

  • 0 in reply to Richard Poley
    Prodigy 30 points

    Hi Richard.


    CMPA and CMPB are always non-zero (except for after reset, and operation after reset has not been a problem. Shadowing is not enabled before CMPx are set to non-zero values).

    However I'm using the AQCTLA.bit.ZRO qualifier. In the note you referred to I can't see that this is specifically mentioned as a problem, but I guess that it is a similar case.

    Regards,


    Øyvind