arch/nios2/core/cpu_idle.c

/*
 * Copyright (c) 2016 Intel Corporation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <nanokernel.h>
#include <nano_private.h>

/**
 *
 * @brief Power save idle routine
 *
 * This function will be called by the nanokernel idle loop or possibly within
 * an implementation of _sys_power_save_idle in the microkernel when the
 * '_sys_power_save_flag' variable is non-zero.
 *
 * @return N/A
 */
void nano_cpu_idle(void)
{
	/* Do nothing but unconditionally unlock interrupts and return to the
	 * caller. This CPU does not have any kind of power saving instruction.
	 */
	irq_unlock(NIOS2_STATUS_PIE_MSK);
}

/**
 *
 * @brief Atomically re-enable interrupts and enter low power mode
 *
 * This function is utilized by the nanokernel object "wait" APIs for tasks,
 * e.g. nano_task_lifo_get(), nano_task_sem_take(),
 * nano_task_stack_pop(), and nano_task_fifo_get().
 *
 * INTERNAL
 * The requirements for nano_cpu_atomic_idle() are as follows:
 * 1) The enablement of interrupts and entering a low-power mode needs to be
 *    atomic, i.e. there should be no period of time where interrupts are
 *    enabled before the processor enters a low-power mode.  See the comments
 *    in nano_task_lifo_get(), for example, of the race condition that
 *    occurs if this requirement is not met.
 *
 * 2) After waking up from the low-power mode, the interrupt lockout state
 *    must be restored as indicated in the 'imask' input parameter.
 *
 * @return N/A
 */
void nano_cpu_atomic_idle(unsigned int key)
{
	/* Do nothing but restore IRQ state. This CPU does not have any
	 * kind of power saving instruction.
	 */
	irq_unlock(key);
}