//!
//! This example shows how to setup PWM0 using the inverted output function.
//! This feature allows you to invert the polarity of the PWM output. This
//! example is setup to invert a 25% duty cycle to get a 75% duty cycle every
//! 5 seconds.
//!
//!
//*****************************************************************************
//
// This function sets up UART0 to be used for a console to display information
// as the example is running.
//
//*****************************************************************************
void
InitConsole(void)
{
//
// Enable GPIO port A which is used for UART0 pins.
// TODO: change this to whichever GPIO port you are using.
//
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
//
// Configure the pin muxing for UART0 functions on port A0 and A1.
// This step is not necessary if your part does not support pin muxing.
// TODO: change this to select the port/pin you are using.
//
GPIOPinConfigure(GPIO_PA0_U0RX);
GPIOPinConfigure(GPIO_PA1_U0TX);
//
// Enable UART0 so that we can configure the clock.
//
SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);
//
// Use the internal 16MHz oscillator as the UART clock source.
//
UARTClockSourceSet(UART0_BASE, UART_CLOCK_PIOSC);
//
// Select the alternate (UART) function for these pins.
// TODO: change this to select the port/pin you are using.
//
GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);
//
// Initialize the UART for console I/O.
//
UARTStdioConfig(0, 115200, 16000000);
}
//*****************************************************************************
//
// Configure PWM0 for a 25% duty cycle signal running at 250Hz. This example
// also shows how to invert the PWM signal every 5 seconds for 5 seconds.
//
//*****************************************************************************
int
main(void)
{
//
// Set the clocking to run directly from the external crystal/oscillator.
// TODO: The SYSCTL_XTAL_ value must be changed to match the value of the
// crystal on your board.
//
SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN |
SYSCTL_XTAL_16MHZ);
//
// Set the PWM clock to the system clock.
//
SysCtlPWMClockSet(SYSCTL_PWMDIV_1);
//
// Set up the serial console to use for displaying messages. This is
// just for this example program and is not needed for Timer operation.
//
InitConsole();
//
// The PWM peripheral must be enabled for use.
//
SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);
//
// For this example PWM0 is used with PortB Pin6. The actual port and
// pins used may be different on your part, consult the data sheet for
// more information.
// GPIO port B needs to be enabled so these pins can be used.
// TODO: change this to whichever GPIO port you are using.
//
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
//
// Configure the GPIO pin muxing to select PWM00 functions for these pins.
// This step selects which alternate function is available for these pins.
// This is necessary if your part supports GPIO pin function muxing.
// Consult the data sheet to see which functions are allocated per pin.
// TODO: change this to select the port/pin you are using.
//
GPIOPinConfigure(GPIO_PB6_M0PWM0);
//
// Configure the PWM function for this pin.
// Consult the data sheet to see which functions are allocated per pin.
// TODO: change this to select the port/pin you are using.
//
GPIOPinTypePWM(GPIO_PORTB_BASE, GPIO_PIN_6);
//
// Configure the PWM0 to count up/down without synchronization.
//
PWMGenConfigure(PWM0_BASE, PWM_GEN_0, PWM_GEN_MODE_UP_DOWN |
PWM_GEN_MODE_NO_SYNC);
//
// Set the PWM period to 250Hz. To calculate the appropriate parameter
// use the following equation: N = (1 / f) * SysClk. Where N is the
// function parameter, f is the desired frequency, and SysClk is the
// system clock frequency.
// In this case you get: (1 / 250Hz) * 16MHz = 64000 cycles. Note that
// the maximum period you can set is 2^16.
// TODO: modify this calculation to use the clock frequency that you are
// using.
//
PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, 64000);
//
// Set PWM0 to a duty cycle of 25%. You set the duty cycle as a function
// of the period. Since the period was set above, you can use the
// PWMGenPeriodGet() function. For this example the PWM will be high for
// 25% of the time or 16000 clock ticks (64000 / 4).
//
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0,
PWMGenPeriodGet(PWM0_BASE, PWM_OUT_0) / 4);
//
// Enable the PWM generator block.
//
PWMGenEnable(PWM0_BASE, PWM_GEN_0);
//
// Loop forever while the PWM signals are generated.
//
while(1)
{
//
// Print out that the level of PWM is normal.
//
UARTprintf("Normal \b\b\b\b\b\b\b\b");
//
// This function provides a means of generating a constant length
// delay. The function delay (in cycles) = 3 * parameter. Delay
// 5 seconds arbitrarily.
//
SysCtlDelay((SysCtlClockGet() * 1) / 3);
//
// Print out that the level of PWM is inverted.
//
UARTprintf("Inverted\b\b\b\b\b\b\b\b");
//
// This function provides a means of generating a constant length
// delay. The function delay (in cycles) = 3 * parameter. Delay
// 5 seconds arbitrarily.
//
SysCtlDelay((SysCtlClockGet() * 1) / 3);
//
// Switch PWM0 signal back to regular operation.
//
PWMOutputInvert(PWM0_BASE, PWM_OUT_0_BIT, false);
}
}
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