esp-idf/components/soc/esp32/rtc_time.c

// Copyright 2015-2017 Espressif Systems (Shanghai) PTE LTD
//
// 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 <stdint.h>
#include "rom/ets_sys.h"
#include "soc/rtc.h"
#include "soc/rtc_cntl_reg.h"
#include "soc/timer_group_reg.h"

#define MHZ (1000000)

/* Calibration of RTC_SLOW_CLK is performed using a special feature of TIMG0.
 * This feature counts the number of XTAL clock cycles within a given number of
 * RTC_SLOW_CLK cycles.
 *
 * Slow clock calibration feature has two modes of operation: one-off and cycling.
 * In cycling mode (which is enabled by default on SoC reset), counting of XTAL
 * cycles within RTC_SLOW_CLK cycle is done continuously. Cycling mode is enabled
 * using TIMG_RTC_CALI_START_CYCLING bit. In one-off mode counting is performed
 * once, and TIMG_RTC_CALI_RDY bit is set when counting is done. One-off mode is
 * enabled using TIMG_RTC_CALI_START bit.
 */

/**
 * @brief Clock calibration function used by rtc_clk_cal and rtc_clk_cal_ratio
 * @param cal_clk which clock to calibrate
 * @param slowclk_cycles number of slow clock cycles to count
 * @return number of XTAL clock cycles within the given number of slow clock cycles
 */
static uint32_t rtc_clk_cal_internal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
{
    /* Enable requested clock (150k clock is always on) */
    if (cal_clk == RTC_CAL_32K_XTAL) {
        SET_PERI_REG_MASK(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_DIG_XTAL32K_EN);
    }
    if (cal_clk == RTC_CAL_8MD256) {
        SET_PERI_REG_MASK(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_DIG_CLK8M_D256_EN);
    }
    /* Prepare calibration */
    REG_SET_FIELD(TIMG_RTCCALICFG_REG(0), TIMG_RTC_CALI_CLK_SEL, cal_clk);
    CLEAR_PERI_REG_MASK(TIMG_RTCCALICFG_REG(0), TIMG_RTC_CALI_START_CYCLING);
    REG_SET_FIELD(TIMG_RTCCALICFG_REG(0), TIMG_RTC_CALI_MAX, slowclk_cycles);
    /* Figure out how long to wait for calibration to finish */
    uint32_t expected_freq;
    rtc_slow_freq_t slow_freq = REG_GET_FIELD(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_ANA_CLK_RTC_SEL);
    if (cal_clk == RTC_CAL_32K_XTAL ||
        (cal_clk == RTC_CAL_RTC_MUX && slow_freq == RTC_SLOW_FREQ_32K_XTAL)) {
        expected_freq = 32768; /* standard 32k XTAL */
    } else if (cal_clk == RTC_CAL_8MD256 ||
            (cal_clk == RTC_CAL_RTC_MUX && slow_freq == RTC_SLOW_FREQ_8MD256)) {
        expected_freq = RTC_FAST_CLK_FREQ_APPROX / 256;
    } else {
        expected_freq = 150000; /* 150k internal oscillator */
    }
    uint32_t us_time_estimate = (uint32_t) (((uint64_t) slowclk_cycles) * MHZ / expected_freq);
    /* Start calibration */
    CLEAR_PERI_REG_MASK(TIMG_RTCCALICFG_REG(0), TIMG_RTC_CALI_START);
    SET_PERI_REG_MASK(TIMG_RTCCALICFG_REG(0), TIMG_RTC_CALI_START);
    /* Wait the expected time calibration should take.
     * TODO: if running under RTOS, and us_time_estimate > RTOS tick, use the
     * RTOS delay function.
     */
    ets_delay_us(us_time_estimate);
    /* Wait for calibration to finish up to another us_time_estimate */
    int timeout_us = us_time_estimate;
    while (!GET_PERI_REG_MASK(TIMG_RTCCALICFG_REG(0), TIMG_RTC_CALI_RDY) &&
            timeout_us > 0) {
        timeout_us--;
        ets_delay_us(1);
    }
    if (cal_clk == RTC_CAL_32K_XTAL) {
        CLEAR_PERI_REG_MASK(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_DIG_XTAL32K_EN);
    }
    if (cal_clk == RTC_CAL_8MD256) {
        CLEAR_PERI_REG_MASK(RTC_CNTL_CLK_CONF_REG, RTC_CNTL_DIG_CLK8M_D256_EN);
    }
    if (timeout_us == 0) {
        /* timed out waiting for calibration */
        return 0;
    }

    return REG_GET_FIELD(TIMG_RTCCALICFG1_REG(0), TIMG_RTC_CALI_VALUE);
}

uint32_t rtc_clk_cal_ratio(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
{
    uint64_t xtal_cycles = rtc_clk_cal_internal(cal_clk, slowclk_cycles);
    uint64_t ratio_64 = ((xtal_cycles << RTC_CLK_CAL_FRACT)) / slowclk_cycles;
    uint32_t ratio = (uint32_t)(ratio_64 & UINT32_MAX);
    return ratio;
}

uint32_t rtc_clk_cal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
{
    rtc_xtal_freq_t xtal_freq = rtc_clk_xtal_freq_get();
    uint64_t xtal_cycles = rtc_clk_cal_internal(cal_clk, slowclk_cycles);
    uint64_t divider = ((uint64_t)xtal_freq) * slowclk_cycles;
    uint64_t period_64 = ((xtal_cycles << RTC_CLK_CAL_FRACT) + divider / 2 - 1) / divider;
    uint32_t period = (uint32_t)(period_64 & UINT32_MAX);
    return period;
}

uint64_t rtc_time_us_to_slowclk(uint64_t time_in_us, uint32_t period)
{
    /* Overflow will happen in this function if time_in_us >= 2^45, which is about 400 days.
     * TODO: fix overflow.
     */
    return (time_in_us << RTC_CLK_CAL_FRACT) / period;
}

uint64_t rtc_time_slowclk_to_us(uint64_t rtc_cycles, uint32_t period)
{
    return (rtc_cycles * period) >> RTC_CLK_CAL_FRACT;
}

uint64_t rtc_time_get()
{
    SET_PERI_REG_MASK(RTC_CNTL_TIME_UPDATE_REG, RTC_CNTL_TIME_UPDATE);
    while (GET_PERI_REG_MASK(RTC_CNTL_TIME_UPDATE_REG, RTC_CNTL_TIME_VALID) == 0) {
        ets_delay_us(1); // might take 1 RTC slowclk period, don't flood RTC bus
    }
    SET_PERI_REG_MASK(RTC_CNTL_INT_CLR_REG, RTC_CNTL_TIME_VALID_INT_CLR);
    uint64_t t = READ_PERI_REG(RTC_CNTL_TIME0_REG);
    t |= ((uint64_t) READ_PERI_REG(RTC_CNTL_TIME1_REG)) << 32;
    return t;
}