drivers: rtc: stm32: add calibration feature
This adds the set_calibration and get_calibration API functions to the STM32 RTC driver Signed-off-by: Johan Lafon <johan.lafon@syslinbit.com>
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@ -1,5 +1,6 @@
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/*
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* Copyright (c) 2023 Prevas A/S
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* Copyright (c) 2023 Syslinbit
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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@ -15,6 +16,7 @@
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#include <zephyr/drivers/rtc.h>
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#include <zephyr/drivers/clock_control/stm32_clock_control.h>
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#include <zephyr/drivers/clock_control.h>
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#include <zephyr/sys/util.h>
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#include <soc.h>
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#include <stm32_ll_pwr.h>
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#include <stm32_ll_rcc.h>
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@ -30,6 +32,29 @@ LOG_MODULE_REGISTER(rtc_stm32, CONFIG_RTC_LOG_LEVEL);
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/* struct tm start: 1st, Jan, 1900 */
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#define TM_TO_RTC_OFFSET 100
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/* Convert part per billion calibration value to a number of clock pulses added or removed each
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* 2^20 clock cycles so it is suitable for the CALR register fields
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*
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* nb_pulses = ppb * 2^20 / 10^9 = ppb * 2^11 / 5^9 = ppb * 2048 / 1953125
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*/
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#define PPB_TO_NB_PULSES(ppb) DIV_ROUND_CLOSEST((ppb) * 2048, 1953125)
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/* Convert CALR register value (number of clock pulses added or removed each 2^20 clock cycles)
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* to part ber billion calibration value
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*
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* ppb = nb_pulses * 10^9 / 2^20 = nb_pulses * 5^9 / 2^11 = nb_pulses * 1953125 / 2048
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*/
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#define NB_PULSES_TO_PPB(pulses) DIV_ROUND_CLOSEST((pulses) * 1953125, 2048)
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/* CALP field can only be 512 or 0 as in reality CALP is a single bit field representing 512 pulses
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* added every 2^20 clock cycles
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*/
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#define MAX_CALP (512)
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#define MAX_CALM (511)
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#define MAX_PPB NB_PULSES_TO_PPB(MAX_CALP)
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#define MIN_PPB -NB_PULSES_TO_PPB(MAX_CALM)
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struct rtc_stm32_config {
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LL_RTC_InitTypeDef ll_rtc_config;
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const struct stm32_pclken *pclken;
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@ -154,11 +179,80 @@ static int rtc_stm32_get_time(const struct device *dev, struct rtc_time *timeptr
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return 0;
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}
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#ifdef CONFIG_RTC_CALIBRATION
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static int rtc_stm32_set_calibration(const struct device *dev, int32_t calibration)
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{
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ARG_UNUSED(dev);
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/* Note : calibration is considered here to be ppb value to apply
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* on clock period (not frequency) but with an opposite sign
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*/
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if ((calibration > MAX_PPB) || (calibration < MIN_PPB)) {
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/* out of supported range */
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return -EINVAL;
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}
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int32_t nb_pulses = PPB_TO_NB_PULSES(calibration);
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/* we tested calibration against supported range
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* so theoretically nb_pulses is also within range
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*/
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__ASSERT_NO_MSG(nb_pulses <= MAX_CALP);
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__ASSERT_NO_MSG(nb_pulses >= -MAX_CALM);
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uint32_t calp, calm;
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if (nb_pulses > 0) {
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calp = LL_RTC_CALIB_INSERTPULSE_SET;
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calm = MAX_CALP - nb_pulses;
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} else {
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calp = LL_RTC_CALIB_INSERTPULSE_NONE;
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calm = -nb_pulses;
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}
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/* wait for recalibration to be ok if a previous recalibration occurred */
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if (!WAIT_FOR(LL_RTC_IsActiveFlag_RECALP(RTC) == 0, 100000, k_msleep(1))) {
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return -EIO;
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}
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LL_RTC_DisableWriteProtection(RTC);
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MODIFY_REG(RTC->CALR, RTC_CALR_CALP | RTC_CALR_CALM, calp | calm);
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LL_RTC_EnableWriteProtection(RTC);
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return 0;
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}
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static int rtc_stm32_get_calibration(const struct device *dev, int32_t *calibration)
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{
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ARG_UNUSED(dev);
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uint32_t calp_enabled = LL_RTC_CAL_IsPulseInserted(RTC);
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uint32_t calm = LL_RTC_CAL_GetMinus(RTC);
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int32_t nb_pulses = -((int32_t) calm);
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if (calp_enabled) {
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nb_pulses += MAX_CALP;
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}
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*calibration = NB_PULSES_TO_PPB(nb_pulses);
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return 0;
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}
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#endif /* CONFIG_RTC_CALIBRATION */
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struct rtc_driver_api rtc_stm32_driver_api = {
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.set_time = rtc_stm32_set_time,
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.get_time = rtc_stm32_get_time,
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/* RTC_ALARM not supported */
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/* RTC_UPDATE not supported */
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#ifdef CONFIG_RTC_CALIBRATION
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.set_calibration = rtc_stm32_set_calibration,
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.get_calibration = rtc_stm32_get_calibration,
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#endif /* CONFIG_RTC_CALIBRATION */
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};
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#define RTC_STM32_DEV_CFG(n) \
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