Servo Sweep

1#include <stdint.h>
2#include <stdbool.h>
3#include "inc/hw_memmap.h"
4#include "driverlib/sysctl.h"
5#include "driverlib/gpio.h"
6#include "driverlib/pin_map.h"
7#include "driverlib/pwm.h"
8 
9#define PWM_PERIOD 15625u   // 20 ms at 781.25 kHz -> 50 Hz
10#define PULSE_0DEG   781u   // ~1.0 ms
11#define PULSE_180DEG 1562u  // ~2.0 ms
12 
13static void delayMs(uint32_t ms) { SysCtlDelay((SysCtlClockGet() / 3000) * ms); }
14 
15// Set servo angle 0..180 -> map to pulse width counts
16static void servoWrite(uint32_t deg) {
17    if (deg > 180) deg = 180;
18    uint32_t pulse = PULSE_0DEG + ((PULSE_180DEG - PULSE_0DEG) * deg) / 180;
19    PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0, pulse);
20}
21 
22int main(void) {
23    SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL |
24                   SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);
25    SysCtlPWMClockSet(SYSCTL_PWMDIV_64);                 // PWM clock = sysclk / 64
26 
27    SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);
28    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
29    while (!SysCtlPeripheralReady(SYSCTL_PERIPH_PWM0)) {}
30    while (!SysCtlPeripheralReady(SYSCTL_PERIPH_GPIOB)) {}
31 
32    GPIOPinConfigure(GPIO_PB6_M0PWM0);                   // route PB6 to PWM
33    GPIOPinTypePWM(GPIO_PORTB_BASE, GPIO_PIN_6);
34 
35    PWMGenConfigure(PWM0_BASE, PWM_GEN_0,
36                    PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC);
37    PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, PWM_PERIOD);
38 
39    servoWrite(90);                                      // start centered
40    PWMOutputState(PWM0_BASE, PWM_OUT_0_BIT, true);
41    PWMGenEnable(PWM0_BASE, PWM_GEN_0);
42 
43    while (1) {
44        uint32_t d;
45        for (d = 0; d <= 180; d += 2) { servoWrite(d); delayMs(15); }  // 0 -> 180
46        delayMs(300);
47        for (d = 180; d > 0; d -= 2) { servoWrite(d); delayMs(15); }   // 180 -> 0
48        delayMs(300);
49    }
50}