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// AVR timer interrupt scheduling code.
//
// Copyright (C) 2016,2017 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_dispatch
/****************************************************************
* 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;
// This is "TIFR1 = 1<<OCF1B" - gcc handles that poorly, so it's hand coded
uint8_t dummy;
asm volatile("ldi %0, %2\n out %1, %0"
: "=d"(dummy) : "i"(&TIFR1 - 0x20), "i"(1<<OCF1B));
}
// Activate timer dispatch as soon as possible
void
timer_kick(void)
{
timer_set(timer_get() + 50);
TIFR1 = 1<<OCF1A;
}
static struct timer wrap_timer;
void
timer_reset(void)
{
sched_add_timer(&wrap_timer);
}
DECL_SHUTDOWN(timer_reset);
void
timer_init(void)
{
irqstatus_t flag = irq_save();
// no outputs
TCCR1A = 0;
// Normal Mode
TCCR1B = 1<<CS10;
// Setup for first irq
TCNT1 = 0;
timer_kick();
timer_repeat_set(timer_get() + 50);
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 = { .val = timer_get() };
calc.hi = timer_high;
if (unlikely(TIFR1 & (1<<TOV1))) {
irq_restore(flag);
if (calc.b1 < 0xff)
calc.hi++;
return calc.val;
}
irq_restore(flag);
return calc.val;
}
// Timer that runs every ~2ms - allows 16bit comparison optimizations
static uint_fast8_t
timer_event(struct timer *t)
{
union u32_u *nextwake = (void*)&wrap_timer.waketime;
if (TIFR1 & (1<<TOV1)) {
// Hardware timer has overflowed - update overflow counter
TIFR1 = 1<<TOV1;
timer_high++;
*nextwake = (union u32_u){ .hi = timer_high, .lo = 0x8000 };
} else {
*nextwake = (union u32_u){ .hi = timer_high + 1, .lo = 0x0000 };
}
return SF_RESCHEDULE;
}
static struct timer wrap_timer = {
.func = timer_event,
.waketime = 0x8000,
};
#define TIMER_IDLE_REPEAT_TICKS 8000
#define TIMER_REPEAT_TICKS 3000
#define TIMER_MIN_ENTRY_TICKS 44
#define TIMER_MIN_EXIT_TICKS 47
#define TIMER_MIN_TRY_TICKS (TIMER_MIN_ENTRY_TICKS + TIMER_MIN_EXIT_TICKS)
#define TIMER_DEFER_REPEAT_TICKS 256
// Hardware timer IRQ handler - dispatch software timers
ISR(TIMER1_COMPA_vect)
{
uint16_t next;
for (;;) {
// Run the next software timer
next = sched_timer_dispatch();
for (;;) {
int16_t diff = timer_get() - next;
if (likely(diff >= 0)) {
// Another timer is pending - briefly allow irqs and then run it
irq_enable();
if (unlikely(TIFR1 & (1<<OCF1B)))
goto check_defer;
irq_disable();
break;
}
if (likely(diff <= -TIMER_MIN_TRY_TICKS))
// Schedule next timer normally
goto done;
irq_enable();
if (unlikely(TIFR1 & (1<<OCF1B)))
goto check_defer;
irq_disable();
continue;
check_defer:
// Check if there are too many repeat timers
irq_disable();
uint16_t now = timer_get();
if ((int16_t)(next - now) < (int16_t)(-timer_from_us(1000)))
try_shutdown("Rescheduled timer in the past");
if (sched_tasks_busy()) {
timer_repeat_set(now + TIMER_REPEAT_TICKS);
next = now + TIMER_DEFER_REPEAT_TICKS;
goto done;
}
timer_repeat_set(now + TIMER_IDLE_REPEAT_TICKS);
timer_set(now);
}
}
done:
timer_set(next);
}
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