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| -rw-r--r-- | src/generic/armcm_timer.c | 136 |
1 files changed, 136 insertions, 0 deletions
diff --git a/src/generic/armcm_timer.c b/src/generic/armcm_timer.c new file mode 100644 index 00000000..f1bc11fa --- /dev/null +++ b/src/generic/armcm_timer.c @@ -0,0 +1,136 @@ +// Timer based on ARM Cortex-M3/M4 SysTick and DWT logic +// +// Copyright (C) 2017-2019 Kevin O'Connor <kevin@koconnor.net> +// +// This file may be distributed under the terms of the GNU GPLv3 license. + +#include "autoconf.h" // CONFIG_CLOCK_FREQ +#include "board/internal.h" // SysTick +#include "board/irq.h" // irq_disable +#include "board/misc.h" // timer_from_us +#include "command.h" // shutdown +#include "sched.h" // sched_timer_dispatch + +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); +} + +// 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 +timer_is_before(uint32_t time1, uint32_t time2) +{ + return (int32_t)(time1 - time2) < 0; +} + +// Set the next irq time +static void +timer_set_diff(uint32_t value) +{ + SysTick->LOAD = value; + SysTick->VAL = 0; + SysTick->LOAD = 0; +} + +// Return the current time (in absolute clock ticks). +uint32_t +timer_read_time(void) +{ + return DWT->CYCCNT; +} + +// Activate timer dispatch as soon as possible +void +timer_kick(void) +{ + SysTick->LOAD = 0; + SysTick->VAL = 0; + SCB->ICSR = SCB_ICSR_PENDSTSET_Msk; +} + +void +timer_init(void) +{ + // Enable Debug Watchpoint and Trace (DWT) for its 32bit timer + CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk; + DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk; + DWT->CYCCNT = 0; + + // Enable SysTick + irqstatus_t flag = irq_save(); + NVIC_SetPriority(SysTick_IRQn, 2); + SysTick->CTRL = (SysTick_CTRL_CLKSOURCE_Msk | SysTick_CTRL_TICKINT_Msk + | SysTick_CTRL_ENABLE_Msk); + timer_kick(); + irq_restore(flag); +} +DECL_INIT(timer_init); + +static uint32_t timer_repeat_until; +#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(2) +#define TIMER_DEFER_REPEAT_TICKS timer_from_us(5) + +// Invoke timers +static uint32_t +timer_dispatch_many(void) +{ + uint32_t tru = timer_repeat_until; + for (;;) { + // Run the next software timer + uint32_t next = sched_timer_dispatch(); + + uint32_t now = timer_read_time(); + int32_t diff = next - now; + if (diff > (int32_t)TIMER_MIN_TRY_TICKS) + // Schedule next timer normally. + return diff; + + if (unlikely(timer_is_before(tru, now))) { + // Check if there are too many repeat timers + if (diff < (int32_t)(-timer_from_us(1000))) + try_shutdown("Rescheduled timer in the past"); + if (sched_tasks_busy()) { + timer_repeat_until = now + TIMER_REPEAT_TICKS; + return TIMER_DEFER_REPEAT_TICKS; + } + timer_repeat_until = tru = now + TIMER_IDLE_REPEAT_TICKS; + } + + // Next timer in the past or near future - wait for it to be ready + irq_enable(); + while (unlikely(diff > 0)) + diff = next - timer_read_time(); + irq_disable(); + } +} + +// IRQ handler +void __visible __aligned(16) // aligning helps stabilize perf benchmarks +SysTick_Handler(void) +{ + irq_disable(); + uint32_t diff = timer_dispatch_many(); + timer_set_diff(diff); + irq_enable(); +} + +// Make sure timer_repeat_until doesn't wrap 32bit comparisons +void +timer_task(void) +{ + uint32_t now = timer_read_time(); + irq_disable(); + if (timer_is_before(timer_repeat_until, now)) + timer_repeat_until = now; + irq_enable(); +} +DECL_TASK(timer_task); |