[LM3S2965] PWM 제어

[LM3S2965] PWM 제어




Luminary Micro Cortex-M3 LM3S2965 PWM
예제소스코드
pwmgen.zip

The following example shows how to initialize the PWM Generator 0 with a 25-KHz frequency, and
with a 25% duty cycle on the PWM0 pin and a 75% duty cycle on the PWM1 pin. This example assumes
the system clock is 20 MHz.
1. Enable the PWM clock by writing a value of 0x0010.0000 to the RCGC0 register in the System
Control module.
2. Enable the clock to the appropriate GPIO module via the RCGC2 register in the System Control
module.
3. In the GPIO module, enable the appropriate pins for their alternate function using the
GPIOAFSEL register.
4. Configure the Run-Mode Clock Configuration (RCC) register in the System Control module
to use the PWM divide (USEPWMDIV) and set the divider (PWMDIV) to divide by 2 (000).
5. Configure the PWM generator for countdown mode with immediate updates to the parameters.
■ Write the PWM0CTL register with a value of 0x0000.0000.
■ Write the PWM0GENA register with a value of 0x0000.008C.
■ Write the PWM0GENB register with a value of 0x0000.080C.
6. Set the period. For a 25-KHz frequency, the period = 1/25,000, or 40 microseconds. The PWM
clock source is 10 MHz; the system clock divided by 2. This translates to 400 clock ticks per
period. Use this value to set the PWM0LOAD register. In Count-Down mode, set the Load field
in the PWM0LOAD register to the requested period minus one.
■ Write the PWM0LOAD register with a value of 0x0000.018F.
7. Set the pulse width of the PWM0 pin for a 25% duty cycle.
■ Write the PWM0CMPA register with a value of 0x0000.012B.
8. Set the pulse width of the PWM1 pin for a 75% duty cycle.
■ Write the PWM0CMPB register with a value of 0x0000.0063.
9. Start the timers in PWM generator 0.
■ Write the PWM0CTL register with a value of 0x0000.0001.
10. Enable PWM outputs.
■ Write the PWMENABLE register with a value of 0x0000.0003.

PWM초기화 함수
void PwmInit(void)
{
    // Enable the peripherals used by this example.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOG);
 

    //
    // Set GPIO D0 and D1 as PWM pins.  They are used to output the PWM0 and
    // PWM1 signals.
    //
    GPIOPinTypePWM(GPIO_PORTG_BASE, GPIO_PIN_2 | GPIO_PIN_3);

    //
    // Compute the PWM period based on the system clock.
    //
    ulPeriod = SysCtlClockGet() / 50000;

    //
    // Set the PWM period to 50 kHz.
    //
    PWMGenConfigure(PWM_BASE, PWM_GEN_0, PWM_GEN_MODE_UP_DOWN | PWM_GEN_MODE_NO_SYNC);
    PWMGenPeriodSet(PWM_BASE, PWM_GEN_0, ulPeriod);

    //
    // Set PWM0 to a duty cycle of 25% and PWM1 to a duty cycle of 75%.
    //
    PWMPulseWidthSet(PWM_BASE, PWM_OUT_0, ulPeriod/4);
    PWMPulseWidthSet(PWM_BASE, PWM_OUT_1, ulPeriod * 3 / 4);

    //
    // Enable the PWM0 and PWM1 output signals.
    //
    PWMOutputState(PWM_BASE, PWM_OUT_0_BIT | PWM_OUT_1_BIT, true);

    //
    // Enable the PWM generator.
    //
    PWMGenEnable(PWM_BASE, PWM_GEN_0);
}


PWM출력 함수
void PWMPulseWidthSet(unsigned long ulBase, unsigned long ulPWMOut, unsigned long ulWidth)
{
    unsigned long ulGenBase, ulReg;

    //
    // Check the arguments.
    //
    ASSERT(ulBase == PWM_BASE);
    ASSERT(PWMOutValid(ulPWMOut));

    //
    // Compute the generator's base address.
    //
    ulGenBase = PWM_OUT_BADDR(ulBase, ulPWMOut);

    //
    // If the counter is in up/down count mode, divide the width by two.
    //
    if(HWREG(ulGenBase + PWM_O_X_CTL) & PWM_X_CTL_MODE)
    {
        ulWidth /= 2;
    }

    //
    // Get the period.
    //
    ulReg = HWREG(ulGenBase + PWM_O_X_LOAD);

    //
    // Make sure the width is not too large.
    //
    ASSERT(ulWidth < ulReg);

    //
    // Compute the compare value.
    //
    ulReg = ulReg - ulWidth;

    //
    // Write to the appropriate registers.
    //
    if(PWM_IS_OUTPUT_ODD(ulPWMOut))
    {
        HWREG(ulGenBase + PWM_O_X_CMPB) = ulReg;
    }
    else
    {
        HWREG(ulGenBase + PWM_O_X_CMPA) = ulReg;
    }
}

Luminary Micro에서 제공하는 함수는 상당히 복잡하다. 범용으로 사용하기 쉽게 제작하긴 했지만... 쉽다는 장점으로 속도에서는 상당한 문제가 있다.
특히나 모터제어와 같이 PWM출력을 주기적으로 변경해야 하는 루틴이 많을경우 AVR보다 더 느려질 수도 있다.

그래서 PWM 제어 함수를 따로 만들었다.
void PwmSet(unsigned int Speed)
{
   HWREG(PWM_OUT_BADDR(PWM_BASE, PWM_OUT_0) + PWM_O_X_CMPA) = PWM_MAX_VALUE - Speed;
}


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