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// STM32F1 timer interrupt scheduling code.
//
// Copyright (C) 2018 Grigori Goronzy <greg@kinoho.net>
// Copyright (C) 2018 Kevin O'Connor <kevin@koconnor.net>
//
// This file may be distributed under the terms of the GNU GPLv3 license.
#include "autoconf.h"
#include "board/misc.h" // timer_from_us
#include "stm32f1xx.h"
#include "stm32f1xx.h"
#include "stm32f1xx_ll_bus.h"
#include "stm32f1xx_ll_tim.h"
#include "command.h" // shutdown
#include "board/io.h" // readl
#include "board/irq.h" // irq_save
#include "sched.h" // sched_timer_dispatch
/****************************************************************
* Low level timer code
****************************************************************/
DECL_CONSTANT(CLOCK_FREQ, CONFIG_CLOCK_FREQ);
static inline uint32_t
timer_get(void)
{
return LL_TIM_GetCounter(TIM2);
}
static inline void
timer_set(uint32_t next)
{
LL_TIM_OC_SetCompareCH1(TIM2, next);
}
static inline void
timer_repeat_set(uint32_t next)
{
LL_TIM_OC_SetCompareCH2(TIM2, next);
LL_TIM_ClearFlag_CC2(TIM2);
}
// Activate timer dispatch as soon as possible
void
timer_kick(void)
{
timer_set(timer_get() + 50);
LL_TIM_ClearFlag_CC1(TIM2);
}
/****************************************************************
* 16bit hardware timer to 32bit conversion
****************************************************************/
// High bits of timer (top 17 bits)
static uint32_t timer_high;
// Return the current time (in absolute clock ticks).
uint32_t
timer_read_time(void)
{
uint32_t th = readl(&timer_high);
uint32_t cur = timer_get();
// Combine timer_high (high 17 bits) and current time (low 16
// bits) using method that handles rollovers correctly.
return (th ^ cur) + (th & 0x8000);
}
// Update timer_high every 0x8000 clock ticks
static uint_fast8_t
timer_event(struct timer *t)
{
timer_high += 0x8000;
t->waketime = timer_high + 0x8000;
return SF_RESCHEDULE;
}
static struct timer wrap_timer = {
.func = timer_event,
.waketime = 0x8000,
};
void
timer_reset(void)
{
sched_add_timer(&wrap_timer);
}
DECL_SHUTDOWN(timer_reset);
/****************************************************************
* Timer init
****************************************************************/
void
timer_init(void)
{
irqstatus_t flag = irq_save();
LL_APB1_GRP1_EnableClock(LL_APB1_GRP1_PERIPH_TIM2);
LL_TIM_SetPrescaler(TIM2, __LL_TIM_CALC_PSC(SystemCoreClock, CONFIG_CLOCK_FREQ));
LL_TIM_SetCounter(TIM2, 0);
LL_TIM_SetAutoReload(TIM2, 0xFFFF);
LL_TIM_EnableIT_CC1(TIM2);
LL_TIM_CC_EnableChannel(TIM2, LL_TIM_CHANNEL_CH1);
LL_TIM_CC_EnableChannel(TIM2, LL_TIM_CHANNEL_CH2);
NVIC_EnableIRQ(TIM2_IRQn);
NVIC_SetPriority(TIM2_IRQn, 0);
timer_kick();
timer_repeat_set(timer_get() + 50);
timer_reset();
LL_TIM_EnableCounter(TIM2);
irq_restore(flag);
}
DECL_INIT(timer_init);
/****************************************************************
* Main timer dispatch irq handler
****************************************************************/
#define TIMER_IDLE_REPEAT_TICKS timer_from_us(500)
#define TIMER_REPEAT_TICKS timer_from_us(100)
#define TIMER_MIN_TRY_TICKS timer_from_us(1)
#define TIMER_DEFER_REPEAT_TICKS timer_from_us(5)
// Hardware timer IRQ handler - dispatch software timers
void __visible __aligned(16)
TIM2_IRQHandler(void)
{
irq_disable();
LL_TIM_ClearFlag_CC1(TIM2);
uint32_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(LL_TIM_IsActiveFlag_CC2(TIM2)))
goto check_defer;
irq_disable();
break;
}
if (likely(diff <= -TIMER_MIN_TRY_TICKS))
// Schedule next timer normally
goto done;
irq_enable();
if (unlikely(LL_TIM_IsActiveFlag_CC2(TIM2)))
goto check_defer;
irq_disable();
continue;
check_defer:
// Check if there are too many repeat timers
irq_disable();
uint32_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);
irq_enable();
}
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