blob: bd2ed1e3c76fe3e51058d2612e025ef850204f48 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
|
#include "common.h"
#include <avr/io.h>
#include <avr/interrupt.h>
#include "timer.h"
/* prescaler is 1024 */
#define PRESCALER ((1 << CS12) | (1 << CS10))
#if F_CPU == 1000000
/* with divider 1024 each tick is 1024us */
#define US_PER_TICK 1024
#define MAX_US ((uint32_t) 67107840)
#elif F_CPU == 8000000
/* with divider 1024 each clock tick is 128us with a rounding error of 64us
* per second/4ms per minute, since it’s a 16 bit timer we support up to
* 2**16-1 ticks, which is 8388480us (8s) */
#define US_PER_TICK 128
#define MAX_US ((uint32_t) 8388480)
#else
#error "cpu speed not supported"
#endif
/* max/current timer hits */
static volatile uint8_t maxhits, hits;
/* compare value for n-1, last hits */
static uint16_t count, lastcount;
/* accumulated time since last timeout/call to timerHit (us) */
static uint32_t time;
static bool oneshot = false;
ISR(TIMER1_COMPA_vect) {
++hits;
time += (uint32_t) OCR1A * (uint32_t) US_PER_TICK;
if (hits == maxhits-1) {
OCR1A = lastcount;
} else if (hits >= maxhits) {
enableWakeup (WAKE_TIMER);
if (oneshot) {
timerStop ();
}
}
}
/* Check if timer was hit, return time since last restart or 0 if not hit yet
*/
uint32_t timerHit () {
uint32_t ret = 0;
ATOMIC_BLOCK (ATOMIC_FORCEON) {
if (shouldWakeup (WAKE_TIMER)) {
disableWakeup (WAKE_TIMER);
ret = time;
if (!oneshot) {
/* reset timer, start again */
hits = 0;
time = 0;
OCR1A = count;
TCNT1 = 0;
}
}
}
return ret;
}
/* Start a timer that fires every t us
*/
void timerStart (const uint32_t t, const bool once) {
oneshot = once;
hits = 0;
time = 0;
/* reset timer value */
TCNT1 = 0;
/* set ctc (compare timer and clear) mode (part 1) */
TCCR1A = 0;
/* enable compare match interrupt */
TIMSK1 = (1 << OCIE1A);
/* set compare value */
if (t >= MAX_US) {
maxhits = t/MAX_US+1;
count = UINT16_MAX;
lastcount = (t % MAX_US) / US_PER_TICK;
OCR1A = UINT16_MAX;
} else {
maxhits = 1;
const uint16_t tdiv = t / US_PER_TICK;
count = tdiv;
lastcount = tdiv;
OCR1A = tdiv;
}
/* prescaler and ctc (part 2) */
TCCR1B = PRESCALER | (1 << WGM12);
}
void timerStop () {
/* zero clock source */
TCCR1B = 0;
}
|
