GPStracker/soft/ds18b20.c

/*
 * ds18b20.c - single sensor support
 * k4be 2019
 * License: BSD
 */ 

#include <string.h>
#include <util/crc16.h>
#include <util/delay.h>
#include "main.h"
#include "ds18b20.h"
#include "1wire.h"

union {
	signed int t;
	unsigned char owbuffer[9];
} t;

#define MAX_ERRORS 5

void gettemp(void){
	unsigned char i, crc=0, tmp;
	static unsigned char error_cnt;
	unsigned char temp_ok_out = 0;
	float temp;

	if(System.timers.owire) return;

	_delay_ms(1);

	/* No presence pulse (bus short, or no sensor at all): skip straight to
	 * the error accounting below instead of returning here - an early
	 * return would skip re-arming System.timers.owire at the end of this
	 * function, so with no sensor ever connected, this whole function would
	 * run on every single main loop pass (never gated by the timer again)
	 * instead of the intended once-per-4s poll. */
	if(_1WireInit() == 1){
		_1WireWriteByte(0xcc);
		_1WireWriteByte(0xbe);

		for(i=0;i<9;i++){
			tmp = _1WireReadByte();
			t.owbuffer[i] = tmp;
			crc = _crc_ibutton_update(crc, tmp);
		}
		if(!crc){
			/* Reject the power-on-reset scratchpad default (85.0C) still in
			 * place if a conversion never actually completed. */
			if(t.owbuffer[0] != 0x50 || t.owbuffer[1] != 0x05 || t.owbuffer[5] != 0xff || t.owbuffer[7] != 0x10){
				temp = (float)t.t*0.0625;
				System.temperature = temp;
				temp_ok_out = 1;
			}
		}
	}

	if(!temp_ok_out){
		if(error_cnt > MAX_ERRORS){
			System.temperature_ok = 0;
		} else {
			error_cnt++;
		}
	} else {
		error_cnt = 0;
		System.temperature_ok = 1;
	}

	if(_1WireInit() == 1){
		_1WireWriteByte(0xcc);
		_1WireWriteBytePR(0x44);
	}
	atomic_set_uint(&System.timers.owire, ms(4000));
}