Poll temperature on a 10s basis

[temper-clone.git] / timer.c

diff --git a/timer.c b/timer.c
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+++ b/timer.c
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+/*
+ * Timer1 functions for ATTiny85
+ *
+ * Heavily based on code from Ardunio:
+ * https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/cores/arduino/wiring.c
+ *
+ * Copyright (c) 2005-2006 David A. Mellis
+ * Copyright 2018 Jonathan McDowell <noodles@earth.li>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stdbool.h>
+#include <stdlib.h>
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <util/delay.h>
+
+#include <avr/pgmspace.h>
+
+#include "timer.h"
+
+#define clockCyclesPerMicrosecond() (F_CPU / 1000000L)
+/* Prescaler of 64 from CPU_CLK */
+#define MICROSECONDS_PER_TIMER1_OVERFLOW (64 * 256 / clockCyclesPerMicrosecond())
+#define MILLIS_INC (MICROSECONDS_PER_TIMER1_OVERFLOW / 1000)
+#define FRACT_INC ((MICROSECONDS_PER_TIMER1_OVERFLOW % 1000) >> 3)
+#define FRACT_MAX (1000 >> 3)
+
+volatile unsigned long timer1_overflow_count = 0;
+volatile unsigned long timer1_millis = 0;
+static unsigned char timer1_fract = 0;
+
+void timer_init(void)
+{
+       /*
+        * bit 7:   0  (CTC1: Disabled CTC)
+        * bit 6/5: 00 (COM1A1/COM1A0: Disconnect counter from OC1A output)
+        * bit 3-0: 0111 (CS13/CS12/CS11/CS10: CPU_CK/64)
+        */
+       TCCR1 = (1 << CS12) | (1 << CS11) | (1 << CS10);
+
+       /* Initialise counter */
+       TCNT1 = 0;
+
+       /* Disable Timer 1 output compare match interrupt */
+       TIMSK &= ~(OCIE1A | OCIE1B);
+       /* Enable Timer 1 overflow interrupt */
+       TIMSK |= _BV(TOIE1);
+}
+
+unsigned long micros(void)
+{
+       unsigned long m;
+       uint8_t oldSREG = SREG, t;
+
+       cli();
+       m = timer1_overflow_count;
+       t = TCNT1;
+
+       if ((TIFR & _BV(TOV1)) & (t < 255))
+               m++;
+
+       SREG = oldSREG;
+
+       return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond());
+}
+
+unsigned long millis(void)
+{
+       unsigned long m;
+       uint8_t oldSREG = SREG;
+
+       cli();
+       m = timer1_millis;
+       SREG = oldSREG;
+
+       return m;
+}
+
+SIGNAL(TIMER1_OVF_vect)
+{
+       unsigned long m = timer1_millis;
+       unsigned char f = timer1_fract;
+
+       m += MILLIS_INC;
+       f += FRACT_INC;
+       if (f >= FRACT_MAX) {
+               f -= FRACT_MAX;
+               m++;
+       }
+
+       timer1_fract = f;
+       timer1_millis = m;
+       timer1_overflow_count++;
+}