esp-idf/components/soc/esp32/rtc_time.c
Ivan Grokhotkov 6353bc40d7 Add support for 32k XTAL as RTC_SLOW_CLK source
- RTC_CNTL_SLOWCLK_FREQ define is removed; rtc_clk_slow_freq_get_hz
  function can be used instead to get an approximate RTC_SLOW_CLK
  frequency

- Clock calibration is performed at startup. The value is saved and used
  for timekeeping and when entering deep sleep.

- When using the 32k XTAL, startup code will wait for the oscillator to
  start up. This can be possibly optimized by starting a separate task
  to wait for oscillator startup, and performing clock switch in that
  task.

- Fix a bug that 32k XTAL would be disabled in rtc_clk_init.

- Fix a rounding error in rtc_clk_cal, which caused systematic frequency
  error.

- Fix an overflow bug which caused rtc_clk_cal to timeout early if the
  slow_clk_cycles argument would exceed certain value

- Improve 32k XTAL oscillator startup time by introducing bootstrapping
  code, which uses internal pullup/pulldown resistors on 32K_N/32K_P
  pins to set better initial conditions for the oscillator.
2017-04-26 12:43:22 +08:00

138 lines
5.6 KiB
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;
}