Ultrasonic Distance

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/timer.h"
7 
8#define LED_ALL (GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3)
9#define TRIG    GPIO_PIN_2   // PB2
10#define ECHO    GPIO_PIN_3   // PB3
11#define PWM_STEPS 256
12 
13// Software PWM: show the color for 'periods' cycles
14static void showColor(uint8_t r, uint8_t g, uint8_t b, uint32_t periods) {
15    volatile uint32_t p, i;
16    for (p = 0; p < periods; p++)
17        for (i = 0; i < PWM_STEPS; i++) {
18            uint8_t out = 0;
19            if (i < r) out |= GPIO_PIN_1;
20            if (i < g) out |= GPIO_PIN_3;
21            if (i < b) out |= GPIO_PIN_2;
22            GPIOPinWrite(GPIO_PORTF_BASE, LED_ALL, out);
23            SysCtlDelay(2);
24        }
25}
26 
27static void delayUs(uint32_t us) { SysCtlDelay((SysCtlClockGet() / 3000000) * us); }
28 
29// One measurement -> distance in cm (0 = no echo / out of range)
30static uint32_t measureCm(void) {
31    uint32_t start, end, timeout;
32 
33    GPIOPinWrite(GPIO_PORTB_BASE, TRIG, TRIG);           // 10 us trigger pulse
34    delayUs(10);
35    GPIOPinWrite(GPIO_PORTB_BASE, TRIG, 0);
36 
37    timeout = 600000;                                    // wait for echo to go high
38    while (GPIOPinRead(GPIO_PORTB_BASE, ECHO) == 0)
39        if (--timeout == 0) return 0;
40    start = TimerValueGet(TIMER0_BASE, TIMER_A);
41 
42    timeout = 600000;                                    // wait for echo to go low
43    while (GPIOPinRead(GPIO_PORTB_BASE, ECHO) != 0)
44        if (--timeout == 0) return 0;
45    end = TimerValueGet(TIMER0_BASE, TIMER_A);
46 
47    return ((end - start) / 50) / 58;                    // 50 MHz -> us, then us/58 = cm
48}
49 
50int main(void) {
51    SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL |
52                   SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);
53 
54    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
55    while (!SysCtlPeripheralReady(SYSCTL_PERIPH_GPIOF)) {}
56    GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, LED_ALL);
57 
58    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
59    while (!SysCtlPeripheralReady(SYSCTL_PERIPH_GPIOB)) {}
60    GPIOPinTypeGPIOOutput(GPIO_PORTB_BASE, TRIG);
61    GPIOPinTypeGPIOInput(GPIO_PORTB_BASE, ECHO);
62 
63    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER0);        // free-running us timer
64    while (!SysCtlPeripheralReady(SYSCTL_PERIPH_TIMER0)) {}
65    TimerConfigure(TIMER0_BASE, TIMER_CFG_PERIODIC_UP);
66    TimerLoadSet(TIMER0_BASE, TIMER_A, 0xFFFFFFFF);
67    TimerEnable(TIMER0_BASE, TIMER_A);
68 
69    while (1) {
70        uint32_t cm = measureCm();
71        if (cm == 0 || cm > 60) {
72            showColor(0, 0, 40, 20);                     // no reading -> dim blue
73        } else {
74            if (cm < 2)  cm = 2;
75            if (cm > 50) cm = 50;
76            uint8_t t = (uint8_t)(((cm - 2) * 255) / 48);
77            showColor(255 - t, 0, t, 20);                // near = red, far = blue
78        }
79        SysCtlDelay(SysCtlClockGet() / 30);
80    }
81}