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Original question:

TMS320F28377S: PWM: Action Qualifier submodule and shadow load

TMS320F28377S: TMS320F28377S

Stephane Bonnot
Prodigy 60 points
Part Number: TMS320F28377S


Hello ,
Sorry for the very long delay, but I wad very busy this last month.
What I try to do is to change the actions of AQ reg. when CTR = 0 and in the same time load shadow AQ regs to active.
See diagram below for more details

As mentioned in my previous question, I have tested this mechanism and some time, when CTR = 0, the old AQ register. was taking into account.
So, my question is:
   Is this design safe enough or to avoid ?

  • 0
    TI__Mastermind 24380 points

    Hi Stephane, 

    No worries at all, thanks for getting back to me! I will link your previous post here to give this thread the context: https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/1284279/tms320f28377s-pwm-action-qualifier-submodule-and-shadow-load.

    With this, it seems your program is trying to carry out an action qualifier and also update it at the same time, which is not ideal. Generally, if you want something to happen at effectively CTR=0 but are using shadow loading, you can just set it to occur on CMPA, then set CMPA=5. For most applications, 5 is low enough that it's effectively 0, but you don't run into any loading problems. Let me know if you are able to use this method.

    One other option (not as recommended, but still may work for you) is if you are absolutely certain your ISR and, more specifically, update of the AQ in the registers will always occur before CTR=PRD, you could change shadow loading to be on both CTR=0 and PRD so that it updates the AQ before the next CTR=0. However, since ISRs most likely include if statements and state-dependent functions- it's hard to guarantee that this will always remain true especially as you continuously develop/change your program going forward.

    Best Regards,

    Allison