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epwm register changes are not applied

Nicola Haggenmacher
Prodigy 110 points

I'm trying to have two blocks of 3 PWMs each. The first 3 should be synchronized to each other while the other 3 should be shifted by a half period. For this purpose I decided to manipulate the PWM_INIT_MACRO() from the example PM_Sensorless.

The 3d ePWM from the first block should generate a synchronization event when it reaches the Period-Value (in Up-Down count mode). At this point, the following PWMs load 0 to their counter and will be delayed by 180°.

But right after execution of  the PWM_INIT_MACRO() both SYNCOSEL and PHSEN are 0, so the changes are not applied and the code doesn't work. If I apply the changes manually in debug mode, it works. Why are the values not applied to the registers, or are there any other write-commands that cause a reset of the register?

The Code I use is here below, it's almost identical to the example code:

#define PWM_INIT_MACRO(m)                                                    \
         /* Setup Sync*/                                                    \
         m->PwmARegs->TBCTL.bit.SYNCOSEL = 0;       /* Pass through sync-signal to next ePWM*/            \
         m->PwmBRegs->TBCTL.bit.SYNCOSEL = 0;       /* Pass through sync-signal to next ePWM*/            \
         m->PwmCRegs->TBCTL.bit.SYNCOSEL = 2;       /* Sync-Event for next ePWM at Counter = Period. Following ePWMs will have 50% Phase delay */            \
                                                                            \
         /* Allow each timer to be sync'ed*/                                \
         m->PwmARegs->TBCTL.bit.PHSEN = 1;            /*Enable Phase Load */        \
         m->PwmBRegs->TBCTL.bit.PHSEN = 1;                                        \
         m->PwmCRegs->TBCTL.bit.PHSEN = 1;                                        \
                                                                            \
         /* Init Timer-Base Period Register for EPWM1-EPWM3*/                \
         m->PwmARegs->TBPRD = m->pwm.PeriodMax;                                        \
         m->PwmBRegs->TBPRD = m->pwm.PeriodMax;                                        \
         m->PwmCRegs->TBPRD = m->pwm.PeriodMax;                                        \
                                                                            \
         /* Init Timer-Base Phase Register for EPWM1-EPWM3 (Value loaded to Counter on Sync-Event)*/                \
         m->PwmARegs->TBPHS.half.TBPHS = 0;                                    \
         m->PwmBRegs->TBPHS.half.TBPHS = 0;                                    \
         m->PwmCRegs->TBPHS.half.TBPHS = 0;                                    \
                                                                            \
         /* Init Timer-Base Control Register for EPWM1-EPWM3*/                \
         m->PwmARegs->TBCTL.all = PWM_INIT_STATE;    /* Count Up-Down, After Sync start with up Count,... */                            \
         m->PwmBRegs->TBCTL.all = PWM_INIT_STATE;                                \
         m->PwmCRegs->TBCTL.all = PWM_INIT_STATE;                                \
                                                                            \
         /* Init Compare Control Register for EPWM1-EPWM3*/                    \
         m->PwmARegs->CMPCTL.all = CMPCTL_INIT_STATE;        /*Load from Shadowed Registers when Counter is at 0*/                    \
         m->PwmBRegs->CMPCTL.all = CMPCTL_INIT_STATE;                            \
         m->PwmCRegs->CMPCTL.all = CMPCTL_INIT_STATE;                            \
                                                                            \
         /* Init Action Qualifier Output A Register for EPWM1-EPWM3*/        \
         m->PwmARegs->AQCTLA.all = AQCTLA_INIT_STATE;        /* SET when counting Up, CLEAR when counting down*/                    \
         m->PwmBRegs->AQCTLA.all = AQCTLA_INIT_STATE;                            \
         m->PwmCRegs->AQCTLA.all = AQCTLA_INIT_STATE;                            \
                                                                            \
         /* Init Dead-Band Generator Control Register for EPWM1-EPWM3*/        \
         m->PwmARegs->DBCTL.all = DBCTL_INIT_STATE;        /* Enable Dead-Band Module, Dead-Band (both signals low during this time) */            \
         m->PwmBRegs->DBCTL.all = DBCTL_INIT_STATE;                            \
         m->PwmCRegs->DBCTL.all = DBCTL_INIT_STATE;                            \
                                                                            \
         /* Init Dead-Band Generator for EPWM1-EPWM3*/                        \
         m->PwmARegs->DBFED = DBCNT_INIT_STATE;            /* Set number of delay-counts between switching edges */                \
         m->PwmARegs->DBRED = DBCNT_INIT_STATE;                                \
         m->PwmBRegs->DBFED = DBCNT_INIT_STATE;                                \
         m->PwmBRegs->DBRED = DBCNT_INIT_STATE;                                \
         m->PwmCRegs->DBFED = DBCNT_INIT_STATE;                                \
         m->PwmCRegs->DBRED = DBCNT_INIT_STATE;                                \
                                                                            \
         /* Init PWM Chopper Control Register for EPWM1-EPWM3*/                \
         m->PwmARegs->PCCTL.all = PCCTL_INIT_STATE;            /* No PWM-Chopping*/                \
         m->PwmBRegs->PCCTL.all = PCCTL_INIT_STATE;                            \
         m->PwmCRegs->PCCTL.all = PCCTL_INIT_STATE;                            \
                                                                            \
         EALLOW;                       /* Enable EALLOW */                    \
                                                                            \
         /* Init Trip Zone Select Register*/                                \
         m->PwmARegs->TZSEL.all = TZSEL_INIT_STATE;                            \
         m->PwmBRegs->TZSEL.all = TZSEL_INIT_STATE;                            \
         m->PwmCRegs->TZSEL.all = TZSEL_INIT_STATE;                            \
                                                                             \
         /* Init Trip Zone Control Register*/                                \
         m->PwmARegs->TZCTL.all = TZCTL_INIT_STATE;                            \
         m->PwmBRegs->TZCTL.all = TZCTL_INIT_STATE;                            \
         m->PwmCRegs->TZCTL.all = TZCTL_INIT_STATE;                            \
                                                                            \
         EDIS;                         /* Disable EALLOW*/   

  • 0
    TI__Guru 57255 points

    Hello Frau Haggenmacher,

    Thoughts:
    1) make sure you do a Rebuild All.  Sometimes the IDE is not completely competent when the header files changes (and the header file contains macroed source code).
    2) Make sure that m is defined as the PWMs you wish to edit.  Is any of the code in your edited file correctly writing registers?
    3) May be a bad comment, but you may also want to double-check that CCS is looking at your edited version vs the library version.

    ===

    Aside: I would recommend having the first PWM be the master PWM and then all other PWMs synch to it - the other two (in your first group of three) having no offset; the other set of three with a 180degree offset.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Prodigy 110 points
    Hi Brett,

    thanks for your comments, actually it helped me to double check the code and I found the reason for the changes not to be applied: shortly after writing to single bits of the TBCTL register, the whole register is written. Since this part of code comes from the PM_Sensorless example, I suggest TI should revise the code...
    But anyway: I think I will follow your suggestion and synchronize all PWM to the same source and just add the phase shift to the synchronization value.

    Best regards
    Nicola

    PS: I don't know where you got the "Frau" from, but let me tell you that you got it wrong ;-)
  • 0 in reply to Nicola Haggenmacher
    TI__Guru 57255 points

    Glad to have helped.

    On the P.S. note:  Sorry about this.  :(


    -Brett

  • 0 in reply to Brett Larimore
    Prodigy 110 points

    Hi,

    I finally implemented the PWM-Groups with 180° phase delay, but it cost me some time since the behavior wasn't as expected.

    First I tried to pass through the SYNC signal to all ePWM Modules (SYNCOSEL = 0) and synchronize them all by writing a ePWM1.TBCTL.bit.SWSYNC = 1. The first group of PWM had to load 0 into the counter while the second group had to load the same value as in the TBPRD register, resulting in a 180° phase shift. But this did not work: the phase shift was not 180° and even worse, it changed every time I triggered SWSYNC !  I even tried to Synchronize all the clocks by deactivating and re-activating TBCLKSYNC, with no effect at all.

    What I found out as a working solution is to synchronize all the PWMs from the first group to TBCTR = 0 (SYNCOSEL = 1) and to pass through the sync-signal in the second group (SYNCOSEL = 0). The value in TBPHS remains 0 for the first ones and TBPRD for the latter.

    The Scope image shows now that both the PWMs and the ISR that are triggered by the PWM have 180° phase shift. Signals 1 and 3 show the signal of ePWM1 and ePWM4. Signal 2 and 4 show the duration of the execution of the ISR which is triggered at TBCTR = 0 of ePWM1 or ePWM4 respectively (ISR starts in the middle of the LOW-time of the pwm, at the same time the ADC is also triggered, current in phase A & B is measured).

  • 0 in reply to Nicola Haggenmacher
    TI__Guru 57255 points

    Hello Herr Haggenmacher,

    Glad you were able to figure it out! 

    As you likely found, Figure 3-5 and Figure 3-7 in the current F2806x TRM are often helpful for comprehending ePWM synchronization.


    Thank you,
    Brett