cputemp.c

/**
 * Author: Dino Ciuffetti - dam2000 at gmail dot com
 * Home: https://github.com/dam2k/fanChat
 * Date: 2019-10-27
 * Whatis: Melopero's FanHat Raspberry Pi FAN controller daemon rethinked from scratch and written in C
 * Work with: Melopero FAN HAT for Raspberry Pi 4
 *   https://www.melopero.com/shop/melopero-engineering/melopero-fan-hat-for-raspberry-pi-4/
 * Requires: PiGpio library: http://abyz.me.uk/rpi/pigpio/ - apt update && apt install libpigpio-dev
 * Replaces: official fan driver written in python: https://www.melopero.com/fan-hat/
 * License: MIT License - https://opensource.org/licenses/MIT
 *
 * Notes:
 * The Melopero FAN HAT for Raspberry Pi 4 is a cool (freddo!! :-)) fan driver for Raspberry Pi 4. It works using GPIO PIN 18 that
 * has hardware driven PWM capabilities. This way they can handle fan speed changing the PIN's duty cycle.
 * We continuously read the CPU temperature thanks to the /sys/class/thermal/thermal_zone0/temp file and we take care of cooling
 * the CPU by setting up the right fan speed modulating the pin's PWM attached to the fan hat.
 * Since I really hate when the fan is always on at low speed, I thinked of using a high and low watermarks.
 * If the cpu's temperature is below the LW the fan will be shut down, and when the cpu's temperature raises above the HW the fan
 * will come into play at the right speed. Also, there is a trigger timeout that will fire if the fan is down for more then a few
 * minutes after the LW event. In this way we can cool down the RPI's temperature a little bit without reaching the HW or
 * stressing us too much. Enjoy it!!
 */

/**
 * Copyright 2019 Dino Ciuffetti - dam2000 at gmail dot com
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
 * IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#include "common.h"
#include "cputemp.h"

#define CPUTEMPSYSFILE "/sys/class/thermal/thermal_zone0/temp"

// cpu file descriptor
static int cpufd=-1;

// return cpu file descriptor or -1 on errors
static int cputemp_fd(void) {
	if(cpufd!=-1) return cpufd; //return previously opened fd
	cpufd=open(CPUTEMPSYSFILE, O_RDONLY);
	/*
	if(cpufd<0) {
		fprintf(stderr, "Error opening cputemp sysfile %s: %s\n", CPUTEMPSYSFILE, strerror(errno));
		return -1;
	}
	*/
	
	return cpufd;
}

/**
 * close file descriptor
 */
void cputemp_close(void) {
	if(cpufd!=-1) return;
	close(cpufd);
	cpufd=-1;
}

/**
 * Get CPU temperature storing it into T and return -1 on errors or 0 on success
 */
int getcputemp(double *T) {
	ssize_t r;
	char b[8];
	double t;
	int fd;
	
	fd=cputemp_fd();
	if(fd<0) {
		fprintf(stderr, "Error opening cputemp sysfile %s: %s\n", CPUTEMPSYSFILE, strerror(errno));
		return -1;
	}
	r=pread(fd, b, 7, 0); // read up to 7 bytes from CPUTEMPSYSFILE putting data into b
	if(r<0) {
		fprintf(stderr, "Error reading from cputemp sysfile %s: %s\n", CPUTEMPSYSFILE, strerror(errno));
		close(fd);
		return -1;
	}
	
	//printf("b: %s\n", b);
	sscanf(b, "%lf", &t); // convert string to a number
	t /= 1000; // number was expressed in millidegree Celsius, porting it to degree Celsius
	*T=t;
	
	return 0;
}