rtc_api.h

/* mbed Microcontroller Library
 * Copyright (c) 2006-2013 ARM Limited
 * SPDX-License-Identifier: Apache-2.0
 *
 * 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.
 */
 
/** \addtogroup hal */
/** @{*/
 
#ifndef MBED_RTC_API_H
#define MBED_RTC_API_H
 
#include "device.h"
 
#include <time.h>
 
#ifdef __cplusplus
extern "C" {
#endif
 
/**
 * \defgroup hal_rtc RTC hal
 *
 * The RTC hal provides a low level interface to the Real Time Counter (RTC) of a
 * target.
 *
 * # Defined behaviour
 * * The function ::rtc_init is safe to call repeatedly - Verified by test rtc_init_test.
 * * RTC accuracy is at least 10% - Verified by test rtc_accuracy_test.
 * * Init/free doesn't stop RTC from counting - Verified by test rtc_persist_test.
 * * Software reset doesn't stop RTC from counting - Verified by test rtc_reset_test.
 * * Sleep modes don't stop RTC from counting - Verified by test rtc_sleep_test.
 * * Shutdown mode doesn't stop RTC from counting - Not verified.
 * * The functions ::rtc_write/::rtc_read provides availability to set/get RTC time
 * - Verified by test rtc_write_read_test.
 * * The function ::rtc_isenabled returns 1 if the RTC has been initialized and is counting and 0 otherwise - Verified by test rtc_enabled_test.
 * * ::rtc_read may be called before rtc_write. If the RTC time has not been set, this will return the
 *    time since some arbitrary epoch. If the RTC time was set on a previous boot, this will return time
 *    based on what was set then.
 *
 * # Undefined behaviour
 * * Calling any function other than ::rtc_init before the initialisation of the RTC
 *
 * # Potential bugs
 * * Incorrect overflow handling - Verified by rtc_range_test
 * * Glitches due to ripple counter - Verified by rtc_glitch_test
 *
 * @see hal_rtc_tests
 *
 * @{
 */
 
/**
 * \defgroup hal_rtc_tests RTC hal tests
 * The RTC test validate proper implementation of the RTC hal.
 *
 * To run the RTC hal tests use the command:
 *
 *     mbed test -t <toolchain> -m <target> -n tests-mbed_hal-rtc*
 */
 
 
/** Initialize the RTC peripheral
 *
 * Powerup the RTC in perpetration for access. This function must be called
 * before any other RTC functions ares called. This does not change the state
 * of the RTC. It just enables access to it.
 *
 * @note This function is safe to call repeatedly - Tested by rtc_init_test
 *
 * Example Implementation Pseudo Code:
 * @code
 * void rtc_init()
 * {
 *     // Enable clock gate so processor can read RTC registers
 *     POWER_CTRL |= POWER_CTRL_RTC_Msk;
 *
 *     // See if the RTC is already setup
 *     if (!(RTC_STATUS & RTC_STATUS_COUNTING_Msk)) {
 *
 *         // Setup the RTC clock source
 *         RTC_CTRL |= RTC_CTRL_CLK32_Msk;
 *     }
 * }
 * @endcode
 */
void rtc_init(void);
 
/** Deinitialize RTC
 *
 * Powerdown the RTC in preparation for sleep, powerdown or reset. That should only
 * affect the CPU domain and not the time keeping logic.
 * After this function is called no other RTC functions should be called
 * except for ::rtc_init.
 *
 * @note This function does not stop the RTC from counting - Tested by rtc_persist_test
 *
 * Example Implementation Pseudo Code:
 * @code
 * void rtc_free()
 * {
 *     // Disable clock gate since processor no longer needs to read RTC registers
 *     POWER_CTRL &= ~POWER_CTRL_RTC_Msk;
 * }
 * @endcode
 *
 * @note Implementations are allowed to not implement this function if it's impossible or there is
 *     no significant benefit to disabling the RTC. As such, the RTC is allowed to remain initialized
 *     after this function is called if freeing the RTC is not implemented.
 */
void rtc_free(void);
 
/** Check if the RTC has been initialized and is counting
 *
 * @retval 0 The time reported by the RTC is not valid
 * @retval 1 The RTC has been initialized and is counting
 *
 * @note In versions of Mbed before 7.0, this function claimed to return false "if the time had not been set."
 *     However, this was flawed because, in most implementations, it only returned true if the time had been
 *     set *on this boot*. There wasn't, and isn't, a way to detect whether the time was set correctly by a previous
 *     boot. To answer that question, you may wish to check if the time is approximately valid (in the 21st
 *     century), or add another flag at the application level.
 *
 * Example Implementation Pseudo Code:
 * @code
 * int rtc_isenabled()
 * {
 *     if (RTC_STATUS & RTC_STATUS_COUNTING_Msk) {
 *         return 1;
 *     } else {
 *         return 0;
 *     }
 * }
 * @endcode
 */
int rtc_isenabled(void);
 
/** Get the current time from the RTC peripheral
 *
 * @return The current time in seconds
 *
 * @note Some RTCs are not synchronized with the main clock. If
 * this is the case with your RTC then you must read the RTC time
 * in a loop to prevent reading the wrong time due to a glitch.
 * The test rtc_glitch_test is intended to catch this bug.
 *
 * Example implementation for an unsynchronized ripple counter:
 * @code
 * time_t rtc_read()
 * {
 *     uint32_t val;
 *     uint32_t last_val;
 *
 *     // Loop until the same value is read twice
 *     val = RTC_SECONDS;
 *     do {
 *         last_val = val;
 *         val = RTC_SECONDS;
 *     } while (last_val != val);
 *
 *     return (time_t)val;
 * }
 * @endcode
 */
time_t rtc_read(void);
 
/** Write the current time in seconds to the RTC peripheral
 *
 * @param t The current time to be set in seconds.
 *
 * Example Implementation Pseudo Code:
 * @code
 * void rtc_write(time_t t)
 * {
 *     RTC_SECONDS = t;
 * }
 * @endcode
 */
void rtc_write(time_t t);
 
/**@}*/
 
#ifdef __cplusplus
}
#endif
 
#endif
 
/** @}*/