forked from espressif/esp-idf
8ccb2a4990
Small changes to clock calibration value will cause increasing errors
the longer the device runs. Consider the case of deep sleep, assuming
that RTC counter is used for timekeeping:
- before sleep:
time_before = rtc_counter * calibration_val
- after sleep:
time_after = (rtc_counter + sleep_count) * (calibration_val + epsilon)
where 'epsilon' is a small estimation error of 'calibration_val'.
The apparent sleep duration thus will be:
time_after - time_before = sleep_count * (calibration_val + epsilon)
+ rtc_counter * epsilon
Second term on the right hand side is the error in time difference
estimation, it is proportional to the total system runtime (rtc_counter).
To avoid this issue, this change makes RTC_SLOW_CLK calibration value
persistent across restarts. This allows the calibration value update to
be preformed, while keeping time after update same as before the update.
128 lines
4.5 KiB
C
128 lines
4.5 KiB
C
// Copyright 2015-2017 Espressif Systems (Shanghai) PTE LTD
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include <stdint.h>
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#include <sys/cdefs.h>
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#include <sys/time.h>
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#include "sdkconfig.h"
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#include "esp_attr.h"
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#include "esp_log.h"
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#include "esp_clk.h"
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#include "rom/ets_sys.h"
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#include "rom/uart.h"
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#include "rom/rtc.h"
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#include "soc/soc.h"
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#include "soc/rtc.h"
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#include "soc/rtc_cntl_reg.h"
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/* Number of cycles to wait from the 32k XTAL oscillator to consider it running.
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* Larger values increase startup delay. Smaller values may cause false positive
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* detection (i.e. oscillator runs for a few cycles and then stops).
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*/
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#define XTAL_32K_DETECT_CYCLES 32
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#define SLOW_CLK_CAL_CYCLES CONFIG_ESP32_RTC_CLK_CAL_CYCLES
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static void select_rtc_slow_clk(rtc_slow_freq_t slow_clk);
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static const char* TAG = "clk";
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/*
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* This function is not exposed as an API at this point,
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* because FreeRTOS doesn't yet support dynamic changing of
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* CPU frequency. Also we need to implement hooks for
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* components which want to be notified of CPU frequency
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* changes.
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*/
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void esp_clk_init(void)
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{
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rtc_config_t cfg = RTC_CONFIG_DEFAULT();
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rtc_init(cfg);
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rtc_clk_fast_freq_set(RTC_FAST_FREQ_8M);
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#ifdef CONFIG_ESP32_RTC_CLOCK_SOURCE_EXTERNAL_CRYSTAL
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select_rtc_slow_clk(RTC_SLOW_FREQ_32K_XTAL);
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#else
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select_rtc_slow_clk(RTC_SLOW_FREQ_RTC);
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#endif
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uint32_t freq_mhz = CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ;
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rtc_cpu_freq_t freq = RTC_CPU_FREQ_80M;
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switch(freq_mhz) {
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case 240:
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freq = RTC_CPU_FREQ_240M;
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break;
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case 160:
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freq = RTC_CPU_FREQ_160M;
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break;
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default:
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freq_mhz = 80;
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/* no break */
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case 80:
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freq = RTC_CPU_FREQ_80M;
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break;
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}
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// Wait for UART TX to finish, otherwise some UART output will be lost
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// when switching APB frequency
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uart_tx_wait_idle(CONFIG_CONSOLE_UART_NUM);
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rtc_clk_cpu_freq_set(freq);
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}
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void IRAM_ATTR ets_update_cpu_frequency(uint32_t ticks_per_us)
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{
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extern uint32_t g_ticks_per_us_pro; // g_ticks_us defined in ROM for PRO CPU
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extern uint32_t g_ticks_per_us_app; // same defined for APP CPU
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g_ticks_per_us_pro = ticks_per_us;
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g_ticks_per_us_app = ticks_per_us;
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}
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static void select_rtc_slow_clk(rtc_slow_freq_t slow_clk)
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{
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if (slow_clk == RTC_SLOW_FREQ_32K_XTAL) {
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/* 32k XTAL oscillator needs to be enabled and running before it can
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* be used. Hardware doesn't have a direct way of checking if the
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* oscillator is running. Here we use rtc_clk_cal function to count
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* the number of main XTAL cycles in the given number of 32k XTAL
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* oscillator cycles. If the 32k XTAL has not started up, calibration
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* will time out, returning 0.
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*/
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rtc_clk_32k_enable(true);
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uint32_t cal_val = 0;
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uint32_t wait = 0;
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// increment of 'wait' counter equivalent to 3 seconds
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const uint32_t warning_timeout = 3 /* sec */ * 32768 /* Hz */ / (2 * XTAL_32K_DETECT_CYCLES);
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ESP_EARLY_LOGD(TAG, "waiting for 32k oscillator to start up")
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do {
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++wait;
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cal_val = rtc_clk_cal(RTC_CAL_32K_XTAL, XTAL_32K_DETECT_CYCLES);
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if (wait % warning_timeout == 0) {
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ESP_EARLY_LOGW(TAG, "still waiting for 32k oscillator to start up");
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}
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} while (cal_val == 0);
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ESP_EARLY_LOGD(TAG, "32k oscillator ready, wait=%d", wait);
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}
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rtc_clk_slow_freq_set(slow_clk);
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uint32_t cal_val;
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if (SLOW_CLK_CAL_CYCLES > 0) {
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/* TODO: 32k XTAL oscillator has some frequency drift at startup.
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* Improve calibration routine to wait until the frequency is stable.
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*/
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cal_val = rtc_clk_cal(RTC_CAL_RTC_MUX, SLOW_CLK_CAL_CYCLES);
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} else {
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const uint64_t cal_dividend = (1ULL << RTC_CLK_CAL_FRACT) * 1000000ULL;
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cal_val = (uint32_t) (cal_dividend / rtc_clk_slow_freq_get_hz());
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}
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ESP_EARLY_LOGD(TAG, "RTC_SLOW_CLK calibration value: %d", cal_val);
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esp_clk_slowclk_cal_set(cal_val);
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}
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