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
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
// AVR timer interrupt scheduling code.
//
// Copyright (C) 2016 Kevin O'Connor <kevin@koconnor.net>
//
// This file may be distributed under the terms of the GNU GPLv3 license.
#include <avr/interrupt.h> // TCNT1
#include "autoconf.h" // CONFIG_AVR_CLKPR
#include "board/misc.h" // timer_from_us
#include "command.h" // shutdown
#include "irq.h" // irq_save
#include "sched.h" // sched_timer_kick
/****************************************************************
* Low level timer code
****************************************************************/
DECL_CONSTANT(CLOCK_FREQ, CONFIG_CLOCK_FREQ);
// Return the number of clock ticks for a given number of microseconds
uint32_t
timer_from_us(uint32_t us)
{
return us * (CONFIG_CLOCK_FREQ / 1000000);
}
union u32_u {
struct { uint8_t b0, b1, b2, b3; };
struct { uint16_t lo, hi; };
uint32_t val;
};
// Return true if time1 is before time2. Always use this function to
// compare times as regular C comparisons can fail if the counter
// rolls over.
uint8_t __always_inline
timer_is_before(uint32_t time1, uint32_t time2)
{
// This asm is equivalent to:
// return (int32_t)(time1 - time2) < 0;
// But gcc doesn't do a good job with the above, so it's hand coded.
union u32_u utime1 = { .val = time1 };
uint8_t f = utime1.b3;
asm(" cp %A1, %A2\n"
" cpc %B1, %B2\n"
" cpc %C1, %C2\n"
" sbc %0, %D2"
: "+r"(f) : "r"(time1), "r"(time2));
return (int8_t)f < 0;
}
static inline uint16_t
timer_get(void)
{
return TCNT1;
}
static inline void
timer_set(uint16_t next)
{
OCR1A = next;
}
static inline void
timer_repeat_set(uint16_t next)
{
// Timer1B is used to limit the number of timers run from a timer1A irq
OCR1B = next;
TIFR1 = 1<<OCF1B;
}
// Reset the timer - clear settings and dispatch next timer immediately
static void
timer_reset(void)
{
uint16_t now = timer_get();
timer_set(now + 50);
TIFR1 = 1<<OCF1A;
timer_repeat_set(now + 50);
}
DECL_SHUTDOWN(timer_reset);
static void
timer_init(void)
{
if (CONFIG_AVR_CLKPR != -1 && (uint8_t)CONFIG_AVR_CLKPR != CLKPR) {
// Program the clock prescaler
irqstatus_t flag = irq_save();
CLKPR = 0x80;
CLKPR = CONFIG_AVR_CLKPR;
irq_restore(flag);
}
// no outputs
TCCR1A = 0;
// Normal Mode
TCCR1B = 1<<CS10;
// Setup for first irq
irqstatus_t flag = irq_save();
timer_reset();
TIFR1 = 1<<TOV1;
// enable interrupt
TIMSK1 = 1<<OCIE1A;
irq_restore(flag);
}
DECL_INIT(timer_init);
/****************************************************************
* 32bit timer wrappers
****************************************************************/
static uint16_t timer_high;
// Return the current time (in absolute clock ticks).
uint32_t
timer_read_time(void)
{
irqstatus_t flag = irq_save();
union u32_u calc;
calc.val = timer_get();
calc.hi = timer_high;
if (TIFR1 & (1<<TOV1) && calc.lo < 0x8000)
calc.hi++;
irq_restore(flag);
return calc.val;
}
// Called by main code once every millisecond. (IRQs disabled.)
void
timer_periodic(void)
{
if (TIFR1 & (1<<TOV1)) {
// Hardware timer has overflowed - update overflow counter
TIFR1 = 1<<TOV1;
timer_high++;
}
}
#define TIMER_IDLE_REPEAT_TICKS 8000
#define TIMER_REPEAT_TICKS 3000
#define TIMER_MIN_TRY_TICKS 60 // 40 ticks to exit irq; 20 ticks of progress
#define TIMER_DEFER_REPEAT_TICKS 200
// Hardware timer IRQ handler - dispatch software timers
ISR(TIMER1_COMPA_vect)
{
uint16_t next;
for (;;) {
// Run the next software timer
next = sched_timer_dispatch();
int16_t diff = timer_get() - next;
if (likely(diff >= 0)) {
// Another timer is pending - briefly allow irqs to fire
irq_enable();
if (unlikely(TIFR1 & (1<<OCF1B)))
// Too many repeat timers - must exit irq handler
goto force_defer;
irq_disable();
continue;
}
if (likely(diff <= -TIMER_MIN_TRY_TICKS))
// Schedule next timer normally
goto done;
// Next timer in very near future - wait for it to be ready
do {
irq_enable();
if (unlikely(TIFR1 & (1<<OCF1B)))
goto force_defer;
irq_disable();
diff = timer_get() - next;
} while (diff < 0);
}
force_defer:
// Too many repeat timers - force a pause so tasks aren't starved
irq_disable();
uint16_t now = timer_get();
if ((int16_t)(next - now) < (int16_t)(-timer_from_us(1000)))
shutdown("Rescheduled timer in the past");
timer_repeat_set(now + TIMER_REPEAT_TICKS);
next = now + TIMER_DEFER_REPEAT_TICKS;
done:
timer_set(next);
return;
}
// Periodic background task that temporarily boosts priority of
// timers. This helps prioritize timers when tasks are idling.
static void
timer_task(void)
{
irq_disable();
timer_repeat_set(timer_get() + TIMER_IDLE_REPEAT_TICKS);
irq_enable();
}
DECL_TASK(timer_task);
|
