/***************************************************************************//** * @file lp_ticker.c ******************************************************************************* * @section License * <b>(C) Copyright 2015 Silicon Labs, http://www.silabs.com</b> ******************************************************************************* * * 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. * ******************************************************************************/ #include "device.h" #include "clocking.h" #if DEVICE_LPTICKER /******************************************************************************* * The Silicon Labs lp_ticker implementation is mapped on top of an extended RTC * API, since the RTC is available in the lowest energy modes. By default, the * RTC counter is configured to run at 4kHz, giving us a quarter-ms resolution * for the low power timer, which should be good enough for a low power use * case. * * On Silicon Labs devices, the lowest width RTC implementation has a 24-bit * counter, which gets extended with a further 32-bit software counter. This * gives 56 bits of actual width, which with the default speed maps to * 557462 years before the extended RTC counter wraps around. We are pretty * certain no device is going to have that amount of uptime. * (At max speed the wraparound is at 69730 years, which is unlikely as well) ******************************************************************************/ #include "rtc_api.h" #include "rtc_api_HAL.h" #include "lp_ticker_api.h" #include "mbed_critical.h" static int rtc_reserved = 0; void lp_ticker_init() { if(!rtc_reserved) { core_util_critical_section_enter(); rtc_init_real(RTC_INIT_LPTIMER); rtc_set_comp0_handler((uint32_t)lp_ticker_irq_handler); rtc_reserved = 1; core_util_critical_section_exit(); } } void lp_ticker_free() { if(rtc_reserved) { core_util_critical_section_enter(); rtc_free_real(RTC_INIT_LPTIMER); rtc_reserved = 0; core_util_critical_section_exit(); } } void lp_ticker_set_interrupt(timestamp_t timestamp) { uint64_t rtc_compare_value; uint64_t current_ticks = rtc_get_full(); timestamp_t current_time = lp_ticker_read(); /* calculate offset value */ timestamp_t offset = timestamp - current_time; /* If the requested timestamp is too far in the future, we might not be able * to set the interrupt accurately due to potentially having ticked between * calculating the timestamp to set and us calculating the offset. */ if(offset > 0xFFFF0000) offset = 100; /* map offset to RTC value */ // ticks = offset * RTC frequency div 1000000 rtc_compare_value = ((uint64_t)offset * (LOW_ENERGY_CLOCK_FREQUENCY / RTC_CLOCKDIV_INT)) / 1000000; /* If RTC offset is less then 2 RTC ticks, the interrupt won't fire */ if(rtc_compare_value < 2) { rtc_compare_value = 2; } rtc_compare_value += current_ticks; rtc_set_comp0_value(rtc_compare_value, true); } inline void lp_ticker_fire_interrupt(void) { rtc_force_comp0(); } inline void lp_ticker_disable_interrupt() { rtc_enable_comp0(false); } inline void lp_ticker_clear_interrupt() { /* No need to clear interrupt flag, since that already happens at RTC level */ } timestamp_t lp_ticker_read() { lp_ticker_init(); uint64_t ticks_temp; uint64_t ticks = rtc_get_full(); /* ticks = counter tick value * timestamp = value in microseconds * timestamp = ticks * 1.000.000 / RTC frequency */ ticks_temp = (ticks * 1000000) / (LOW_ENERGY_CLOCK_FREQUENCY / RTC_CLOCKDIV_INT); return (timestamp_t) (ticks_temp & 0xFFFFFFFF); } #endif