TM4C1294NCPDT: PWM Generator’s time base synchronisation in up-down count mode with different load or period-match values.

Hello Milan,

Thank you for the image, very helpful for my understanding which is quite crystal clear now.

The answer unfortunately is the fabled: "It Depends"

How tight do you need the synchronization to be?

How often would you be willing to re-synchronize the signals?

Those two questions will be very key in determining what is possible.

In general, the best that can be done for synchronization with two different periods is to clear their counters as closely together as possible. Using the Sync API's do this quite well, but the synchronization doesn't last forever and actually initial degrades quite quickly as within 3-4ms, there is already 300-400ns error in the synchronization. The longer it is left without re-syncing, the more it will get out of sync, at a rate that seems to be roughly 25ns per ms (from just a few crude measurements and calculations).

If you have no tolerance for even small variation or cannot resync often, then based on my findings you wouldn't be able to do what you are hoping for.

Here is the code I used to try this out. I realize now posting this that you also needed center aligned which this doesn't reflect, but I think the principle will be the same.

    uint32_t ui32SysClock;

    ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ | SYSCTL_OSC_MAIN | SYSCTL_USE_PLL | SYSCTL_CFG_VCO_480), 120000000);

    SysCtlPWMClockSet(SYSCTL_PWMDIV_1);

    SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);

    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOK);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOG);

    GPIOPinConfigure(GPIO_PK4_M0PWM6);
    GPIOPinConfigure(GPIO_PG1_M0PWM5);

    GPIOPinTypePWM(GPIO_PORTK_BASE, GPIO_PIN_4);
    GPIOPinTypePWM(GPIO_PORTG_BASE, GPIO_PIN_1);

    PWMGenConfigure(PWM0_BASE, PWM_GEN_3, PWM_GEN_MODE_DOWN | PWM_GEN_MODE_GEN_SYNC_LOCAL);
    PWMGenConfigure(PWM0_BASE, PWM_GEN_2, PWM_GEN_MODE_DOWN | PWM_GEN_MODE_GEN_SYNC_LOCAL);

    PWMGenPeriodSet(PWM0_BASE, PWM_GEN_3, (ui32SysClock / 10000) - 1);
    PWMPulseWidthSet(PWM0_BASE, PWM_OUT_6, (ui32SysClock / 50000) - 1);

    PWMGenPeriodSet(PWM0_BASE, PWM_GEN_2, (ui32SysClock / 20000) - 1);
    PWMPulseWidthSet(PWM0_BASE, PWM_OUT_5, (ui32SysClock / 50000) - 1);

    PWMOutputState(PWM0_BASE, PWM_OUT_6_BIT | PWM_OUT_5_BIT, true);

    PWMGenEnable(PWM0_BASE, PWM_GEN_3);
    PWMGenEnable(PWM0_BASE, PWM_GEN_2);

    PWMSyncTimeBase(PWM0_BASE, PWM_GEN_2_BIT | PWM_GEN_3_BIT);
    PWMSyncUpdate(PWM0_BASE, PWM_GEN_2_BIT | PWM_GEN_3_BIT);

    while(1)
    {
    	// Do Nothing
    	SysCtlDelay(500000);
        PWMSyncTimeBase(PWM0_BASE, PWM_GEN_2_BIT | PWM_GEN_3_BIT);
        PWMSyncUpdate(PWM0_BASE, PWM_GEN_2_BIT | PWM_GEN_3_BIT);
    }