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+/*
+ * MIT License
+ *
+ * Copyright (c) 2020 Joey Castillo
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+////< @file watch_deepsleep.h
+
+/** @addtogroup deepsleep Deep Sleep Control
+  * @brief This section covers functions related to preparing for and entering BACKUP mode, the
+  *        deepest sleep mode available on the SAM L22
+  */
+/// @{
+/** @brief Registers a callback on one of the RTC's external wake pins, which can wake the device
+  * from deep sleep mode.
+  * @param pin Either pin A2 or pin D1, the two external wake pins on the nine-pin connector.
+  * @param callback The callback to be called if this pin triggers outside of deep sleep mode.
+  * @note When in normal or STANDBY mode, this will function much like a standard external interrupt
+  *       situation: these pins will wake from standby, and your callback will be called. However,
+  *       if the device enters deep sleep and one of these pins wakes the device, your callback
+  *       WILL NOT be called.
+  */
+void watch_register_extwake_callback(uint8_t pin, ext_irq_cb_t callback);
+
+/** @brief Stores data in one of the RTC's backup registers, which retain their data in deep sleep.
+  * @param data An unsigned 32 bit integer with the data you wish to store.
+  * @param reg A register from 0-7.
+  */
+void watch_store_backup_data(uint32_t data, uint8_t reg);
+
+/** @brief Gets 32 bits of data from the RTC's backup register, which retains its data in deep sleep.
+  * @param reg A register from 0-7.
+  * @return An unsigned 32 bit integer with the from the backup register.
+  */
+uint32_t watch_get_backup_data(uint8_t reg);
+
+/** @brief Enters the SAM L22's lowest-power mode, BACKUP.
+  * @details This function does some housekeeping before entering BACKUP mode. It first disables all
+  *          peripherals except for the RTC, and disables the tick interrupt (since that would wake)
+  *          us up from deep sleep. It also sets an external wake source on the ALARM button, if one
+  *          was not already set. If you wish to wake from another source, such as one of the external
+  *          wake interrupt pins on the 9-pin connector, set that up prior to calling this function.
+  * @note If you have a callback set for an external wake interrupt, it will be called if triggered while
+  *       in ACTIVE, IDLE or STANDBY modes, but it *will not be called* when waking from BACKUP.
+  *       Waking from backup is effectively like waking from reset, except that your @ref
+  *       app_wake_from_deep_sleep function will be called.
+  * @warning In initial testing, it seems like the ALARM_BTN pin (PA02 RTC/IN2) cannot wake the device
+  *          from deep sleep mode. There is an errata note (Reference: 15010, linked) that says that
+  *          due to a silicon bug, PB01 cannot be used as RTC/IN2. It seems though that this bug may
+  *          also affect PA02. As a result — and I'm very bummed about this — you cannot use deep sleep
+  *          mode unless you set up an external wake interrupt using a device on the nine-pin connector
+  *          (i.e. an accelerometer with an interrupt pin). Otherwise your only option for waking will
+  *          be to unscrew the watch case and press the reset button on the back of the board.
+  *          http://ww1.microchip.com/downloads/en/DeviceDoc/SAM_L22_Family_Errata_DS80000782B.pdf
+  */
+void watch_enter_deep_sleep();
+/// @}