kernel/busy_wait.c

/*
 * Copyright (c) 2018 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/kernel.h>
#include <zephyr/drivers/timer/system_timer.h>
#include <zephyr/sys_clock.h>
#include <kernel_arch_interface.h>

void z_impl_k_busy_wait(uint32_t usec_to_wait)
{
	SYS_PORT_TRACING_FUNC_ENTER(k_thread, busy_wait, usec_to_wait);
	if (usec_to_wait == 0U) {
		SYS_PORT_TRACING_FUNC_EXIT(k_thread, busy_wait, usec_to_wait);
		return;
	}

#if defined(CONFIG_ARCH_HAS_CUSTOM_BUSY_WAIT)
	arch_busy_wait(usec_to_wait);
#elif defined(CONFIG_SYS_CLOCK_EXISTS)
	uint32_t start_cycles = k_cycle_get_32();

	/* use 64-bit math to prevent overflow when multiplying */
	uint32_t cycles_to_wait = (uint32_t)(
		(uint64_t)usec_to_wait *
		(uint64_t)sys_clock_hw_cycles_per_sec() /
		(uint64_t)USEC_PER_SEC
	);

	for (;;) {
		uint32_t current_cycles = k_cycle_get_32();

		/* this handles the rollover on an unsigned 32-bit value */
		if ((current_cycles - start_cycles) >= cycles_to_wait) {
			break;
		}
	}
#else
	/*
	 * Crude busy loop for the purpose of being able to configure out
	 * system timer support.
	 */
	unsigned int loops_per_usec = CONFIG_BUSYWAIT_CPU_LOOPS_PER_USEC;
	unsigned int loops = loops_per_usec * usec_to_wait;

	while (loops-- > 0) {
		arch_nop();
	}
#endif

	SYS_PORT_TRACING_FUNC_EXIT(k_thread, busy_wait, usec_to_wait);
}

#ifdef CONFIG_USERSPACE
static inline void z_vrfy_k_busy_wait(uint32_t usec_to_wait)
{
	z_impl_k_busy_wait(usec_to_wait);
}
#include <syscalls/k_busy_wait_mrsh.c>
#endif /* CONFIG_USERSPACE */