1 files changed, 89 insertions, 0 deletions

diff --git a/common/timer.c b/common/timer.c
new file mode 100644
index 000000000..48a38c9b6
--- /dev/null
+++ b/common/timer.c
@@ -0,0 +1,89 @@
+/*
+Copyright 2011 Jun Wako <wakojun@gmail.com>
+
+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 2 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 <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdint.h>
+#include "timer.h"
+
+
+// counter resolution 1ms
+volatile uint16_t timer_count = 0;
+
+void timer_init(void)
+{
+    // Timer0 CTC mode
+    TCCR0A = 0x02;
+
+#if TIMER_PRESCALER == 1
+    TCCR0B = 0x01;
+#elif TIMER_PRESCALER == 8
+    TCCR0B = 0x02;
+#elif TIMER_PRESCALER == 64
+    TCCR0B = 0x03;
+#elif TIMER_PRESCALER == 256
+    TCCR0B = 0x04;
+#elif TIMER_PRESCALER == 1024
+    TCCR0B = 0x05;
+#else
+#   error "Timer prescaler value is NOT vaild."
+#endif
+
+    OCR0A = TIMER_RAW_TOP;
+    TIMSK0 = (1<<OCIE0A);
+}
+
+inline
+void timer_clear(void)
+{
+    uint8_t sreg = SREG;
+    cli();
+    timer_count = 0;
+    SREG = sreg;
+}
+
+inline
+uint16_t timer_read(void)
+{
+    uint16_t t;
+
+    uint8_t sreg = SREG;
+    cli();
+    t = timer_count;
+    SREG = sreg;
+
+    return t;
+}
+
+inline
+uint16_t timer_elapsed(uint16_t last)
+{
+    uint16_t t;
+
+    uint8_t sreg = SREG;
+    cli();
+    t = timer_count;
+    SREG = sreg;
+
+    return TIMER_DIFF_MS(t, last);
+}
+
+// excecuted once per 1ms.(excess for just timer count?)
+ISR(TIMER0_COMPA_vect)
+{
+    timer_count++;
+}