67 lines
1.9 KiB
C
67 lines
1.9 KiB
C
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// pwm.c
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//
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// Example program for bcm2835 library
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// Shows how to use PWM to control GPIO pins
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//
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// After installing bcm2835, you can build this
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// with something like:
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// gcc -o pwm pwm.c -l bcm2835
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// sudo ./pwm
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//
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// Or you can test it before installing with:
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// gcc -o pwm -I ../../src ../../src/bcm2835.c pwm.c
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// sudo ./pwm
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//
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// Connect an LED between GPIO18 (pin 12) and GND to observe the LED changing in brightness
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//
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// Author: Mike McCauley
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// Copyright (C) 2013 Mike McCauley
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// $Id: RF22.h,v 1.21 2012/05/30 01:51:25 mikem Exp $
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#include <bcm2835.h>
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#include <stdio.h>
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// PWM output on RPi Plug P1 pin 12 (which is GPIO pin 18)
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// in alt fun 5.
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// Note that this is the _only_ PWM pin available on the RPi IO headers
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#define PIN RPI_GPIO_P1_12
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// and it is controlled by PWM channel 0
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#define PWM_CHANNEL 0
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// This controls the max range of the PWM signal
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#define RANGE 1024
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int main(int argc, char **argv)
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{
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if (!bcm2835_init())
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return 1;
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// Set the output pin to Alt Fun 5, to allow PWM channel 0 to be output there
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bcm2835_gpio_fsel(PIN, BCM2835_GPIO_FSEL_ALT5);
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// Clock divider is set to 16.
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// With a divider of 16 and a RANGE of 1024, in MARKSPACE mode,
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// the pulse repetition frequency will be
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// 1.2MHz/1024 = 1171.875Hz, suitable for driving a DC motor with PWM
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bcm2835_pwm_set_clock(BCM2835_PWM_CLOCK_DIVIDER_16);
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bcm2835_pwm_set_mode(PWM_CHANNEL, 1, 1);
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bcm2835_pwm_set_range(PWM_CHANNEL, RANGE);
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// Vary the PWM m/s ratio between 1/RANGE and (RANGE-1)/RANGE
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// over the course of a a few seconds
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int direction = 1; // 1 is increase, -1 is decrease
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int data = 1;
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while (1)
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{
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if (data == 1)
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direction = 1; // Switch to increasing
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else if (data == RANGE-1)
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direction = -1; // Switch to decreasing
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data += direction;
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bcm2835_pwm_set_data(PWM_CHANNEL, data);
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bcm2835_delay(1);
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}
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bcm2835_close();
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return 0;
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}
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