时钟树

ESP32 的时钟子系统用于从一系列根时钟中提取并分配系统/模块时钟。时钟树驱动程序负责维护系统时钟的基本功能，并管理模块时钟间的复杂关系。

本文档首先介绍了根时钟和模块时钟，随后介绍了可供用户调用的时钟树 API，调用这些 API，可以监测模块时钟的运行状态。

简介

本节列出了 ESP32 支持的根时钟和模块时钟的定义，这些定义通常用于驱动程序配置，有助于为外设选择合适的时钟源。

根时钟

根时钟会产生可靠的时钟信号，经各种门、复用器、分频器或倍频器传递，这些时钟信号最终成为 CPU 内核、Wi-Fi、蓝牙、RTC 及外设等功能模块的时钟源。

ESP32 的根时钟列在 soc_root_clk_t 中：

内部 8 MHz RC 振荡器 (RC_FAST)

此 RC 振荡器可产生约 8.5 MHz 的时钟信号输出，标识为 RC_FAST_CLK。

此约 8.5 MHz 的信号也会传入可配置的分频器，默认情况下，该分频器会将输入的时钟频率分频 256 倍，生成信号 RC_FAST_D256_CLK。

在运行时，通过在 RC_FAST_D256_CLK 上校准，可以计算 RC_FAST_CLK 的实际频率。

外部 2 ~ 40 MHz 晶振 (XTAL)

内部 150 kHz RC 振荡器 (RC_SLOW)

此 RC 振荡器产生约 150 kHz 的时钟信号输出，标识为 RC_SLOW_CLK。在运行时，通过校准，可以计算该时钟信号的实际频率。

外部 32 kHz 晶振 - 可选 (XTAL32K)

XTAL32K_CLK 的时钟源可以是连接到 32K_XP 和 32K_XN 管脚的 32 kHz 晶振，也可以是外部电路生成的 32 kHz 时钟信号。如果使用外部电路生成的时钟信号，该信号必须连接到 32K_XN 管脚，并且在 32K_XP 管脚和地之间连接一个 1 nF 的电容。此时，32K_XP 管脚不能用作 GPIO 管脚。

通过校准，可以计算 XTAL32K_CLK 的实际频率。

与晶振产生的信号相比，从 RC 振荡器电路产生的信号通常精度较低，且容易受环境影响。因此，ESP32 为 RTC_SLOW_CLK 提供了几种时钟源选项，可以根据对系统时间精度和对功耗的要求选择。更多详情，请参阅 RTC 定时器时钟源。

模块时钟

ESP32 的可用模块时钟在 soc_module_clk_t 中列出，每个模块时钟都有其唯一 ID。查阅文档中的枚举值，即可获取各模块时钟的详细信息。

使用 API

时钟树驱动程序提供了一个一体化接口，可以获取模块时钟的频率，即 esp_clk_tree_src_get_freq_hz()。通过该函数，你可以在任何时刻，通过提供时钟名称 soc_module_clk_t 和指定返回频率值的精度级别 esp_clk_tree_src_freq_precision_t，获取时钟频率。

API 参考

Header File

components/soc/esp32/include/soc/clk_tree_defs.h

Macros

SOC_CLK_RC_FAST_FREQ_APPROX: Approximate RC_FAST_CLK frequency in Hz

SOC_CLK_RC_SLOW_FREQ_APPROX: Approximate RC_SLOW_CLK frequency in Hz

SOC_CLK_RC_FAST_D256_FREQ_APPROX: Approximate RC_FAST_D256_CLK frequency in Hz

SOC_CLK_XTAL32K_FREQ_APPROX: Approximate XTAL32K_CLK frequency in Hz

SOC_GPTIMER_CLKS

Array initializer for all supported clock sources of GPTimer.

The following code can be used to iterate all possible clocks:

soc_periph_gptimer_clk_src_t gptimer_clks[] = (soc_periph_gptimer_clk_src_t)SOC_GPTIMER_CLKS;
for (size_t i = 0; i< sizeof(gptimer_clks) / sizeof(gptimer_clks[0]); i++) {
    soc_periph_gptimer_clk_src_t clk = gptimer_clks[i];
    // Test GPTimer with the clock `clk`
}

SOC_LCD_CLKS: Array initializer for all supported clock sources of LCD.

SOC_RMT_CLKS: Array initializer for all supported clock sources of RMT.

SOC_MCPWM_TIMER_CLKS: Array initializer for all supported clock sources of MCPWM Timer.

SOC_MCPWM_CAPTURE_CLKS: Array initializer for all supported clock sources of MCPWM Capture Timer.

SOC_MCPWM_CARRIER_CLKS: Array initializer for all supported clock sources of MCPWM Carrier.

SOC_I2S_CLKS: Array initializer for all supported clock sources of I2S.

SOC_I2C_CLKS: Array initializer for all supported clock sources of I2C.

SOC_SPI_CLKS: Array initializer for all supported clock sources of SPI.

SOC_SDM_CLKS: Array initializer for all supported clock sources of SDM.

SOC_DAC_DIGI_CLKS: Array initializer for all supported clock sources of DAC digital controller.

SOC_DAC_COSINE_CLKS: Array initializer for all supported clock sources of DAC cosine wave generator.

SOC_TWAI_CLKS: Array initializer for all supported clock sources of TWAI.

SOC_ADC_DIGI_CLKS: Array initializer for all supported clock sources of ADC digital controller.

SOC_ADC_RTC_CLKS: Array initializer for all supported clock sources of ADC RTC controller.

SOC_MWDT_CLKS: Array initializer for all supported clock sources of MWDT.

SOC_LEDC_CLKS: Array initializer for all supported clock sources of LEDC.

Enumerations

enum soc_root_clk_t

Root clock.

Values:

enumerator SOC_ROOT_CLK_INT_RC_FAST: Internal 8MHz RC oscillator

enumerator SOC_ROOT_CLK_INT_RC_SLOW: Internal 150kHz RC oscillator

enumerator SOC_ROOT_CLK_EXT_XTAL: External 2~40MHz crystal

enumerator SOC_ROOT_CLK_EXT_XTAL32K: External 32kHz crystal/clock signal

enum soc_cpu_clk_src_t

CPU_CLK mux inputs, which are the supported clock sources for the CPU_CLK.

备注

Enum values are matched with the register field values on purpose

Values:

enumerator SOC_CPU_CLK_SRC_XTAL: Select XTAL_CLK as CPU_CLK source

enumerator SOC_CPU_CLK_SRC_PLL: Select PLL_CLK as CPU_CLK source (PLL_CLK is the output of 40MHz crystal oscillator frequency multiplier, can be 480MHz or 320MHz)

enumerator SOC_CPU_CLK_SRC_RC_FAST: Select RC_FAST_CLK as CPU_CLK source

enumerator SOC_CPU_CLK_SRC_APLL: Select APLL_CLK as CPU_CLK source

enumerator SOC_CPU_CLK_SRC_INVALID: Invalid CPU_CLK source

enum soc_rtc_slow_clk_src_t

RTC_SLOW_CLK mux inputs, which are the supported clock sources for the RTC_SLOW_CLK.

备注

Enum values are matched with the register field values on purpose

Values:

enumerator SOC_RTC_SLOW_CLK_SRC_RC_SLOW: Select RC_SLOW_CLK as RTC_SLOW_CLK source

enumerator SOC_RTC_SLOW_CLK_SRC_XTAL32K: Select XTAL32K_CLK as RTC_SLOW_CLK source

enumerator SOC_RTC_SLOW_CLK_SRC_RC_FAST_D256: Select RC_FAST_D256_CLK (referred as FOSC_DIV or 8m_d256/8md256 in TRM and reg. description) as RTC_SLOW_CLK source

enumerator SOC_RTC_SLOW_CLK_SRC_INVALID: Invalid RTC_SLOW_CLK source

enum soc_rtc_fast_clk_src_t

RTC_FAST_CLK mux inputs, which are the supported clock sources for the RTC_FAST_CLK.

备注

Enum values are matched with the register field values on purpose

Values:

enumerator SOC_RTC_FAST_CLK_SRC_XTAL_D4: Select XTAL_D4_CLK (may referred as XTAL_CLK_DIV_4) as RTC_FAST_CLK source

enumerator SOC_RTC_FAST_CLK_SRC_XTAL_DIV: Alias name for SOC_RTC_FAST_CLK_SRC_XTAL_D4

enumerator SOC_RTC_FAST_CLK_SRC_RC_FAST: Select RC_FAST_CLK as RTC_FAST_CLK source

enumerator SOC_RTC_FAST_CLK_SRC_INVALID: Invalid RTC_FAST_CLK source

enum soc_module_clk_t

Supported clock sources for modules (CPU, peripherals, RTC, etc.)

备注

enum starts from 1, to save 0 for special purpose

Values:

enumerator SOC_MOD_CLK_CPU: CPU_CLK can be sourced from XTAL, PLL, RC_FAST, or APLL by configuring soc_cpu_clk_src_t

enumerator SOC_MOD_CLK_RTC_FAST: RTC_FAST_CLK can be sourced from XTAL_D4 or RC_FAST by configuring soc_rtc_fast_clk_src_t

enumerator SOC_MOD_CLK_RTC_SLOW: RTC_SLOW_CLK can be sourced from RC_SLOW, XTAL32K, or RC_FAST_D256 by configuring soc_rtc_slow_clk_src_t

enumerator SOC_MOD_CLK_APB: APB_CLK is highly dependent on the CPU_CLK source

enumerator SOC_MOD_CLK_PLL_D2: PLL_D2_CLK is derived from PLL, it has a fixed divider of 2

enumerator SOC_MOD_CLK_PLL_F160M: PLL_F160M_CLK is derived from PLL, and has a fixed frequency of 160MHz

enumerator SOC_MOD_CLK_XTAL32K: XTAL32K_CLK comes from the external 32kHz crystal, passing a clock gating to the peripherals

enumerator SOC_MOD_CLK_RC_FAST: RC_FAST_CLK comes from the internal 8MHz rc oscillator, passing a clock gating to the peripherals

enumerator SOC_MOD_CLK_RC_FAST_D256: RC_FAST_D256_CLK comes from the internal 8MHz rc oscillator, divided by 256, and passing a clock gating to the peripherals

enumerator SOC_MOD_CLK_XTAL: XTAL_CLK comes from the external crystal (2~40MHz)

enumerator SOC_MOD_CLK_REF_TICK: REF_TICK is derived from APB, it has a fixed frequency of 1MHz even when APB frequency changes

enumerator SOC_MOD_CLK_APLL: APLL is sourced from PLL, and its frequency is configurable through APLL configuration registers

enumerator SOC_MOD_CLK_INVALID: Indication of the end of the available module clock sources

enum soc_periph_systimer_clk_src_t

Type of SYSTIMER clock source.

Values:

enumerator SYSTIMER_CLK_SRC_XTAL: SYSTIMER source clock is XTAL

enumerator SYSTIMER_CLK_SRC_DEFAULT: SYSTIMER source clock default choice is XTAL

enum soc_periph_gptimer_clk_src_t

Type of GPTimer clock source.

Values:

enumerator GPTIMER_CLK_SRC_APB: Select APB as the source clock

enumerator GPTIMER_CLK_SRC_DEFAULT: Select APB as the default choice

enum soc_periph_tg_clk_src_legacy_t

Type of Timer Group clock source, reserved for the legacy timer group driver.

Values:

enumerator TIMER_SRC_CLK_APB: Timer group source clock is APB

enumerator TIMER_SRC_CLK_DEFAULT: Timer group source clock default choice is APB

enum soc_periph_lcd_clk_src_t

Type of LCD clock source.

Values:

enumerator LCD_CLK_SRC_PLL160M: Select PLL_160M as the source clock

enumerator LCD_CLK_SRC_DEFAULT: Select PLL_160M as the default choice

enum soc_periph_rmt_clk_src_t

Type of RMT clock source.

Values:

enumerator RMT_CLK_SRC_APB: Select APB as the source clock

enumerator RMT_CLK_SRC_REF_TICK: Select REF_TICK as the source clock

enumerator RMT_CLK_SRC_DEFAULT: Select APB as the default choice

enum soc_periph_rmt_clk_src_legacy_t

Type of RMT clock source, reserved for the legacy RMT driver.

Values:

enumerator RMT_BASECLK_APB: RMT source clock is APB CLK

enumerator RMT_BASECLK_REF: RMT source clock is REF_TICK

enumerator RMT_BASECLK_DEFAULT: RMT source clock default choice is APB

enum soc_periph_uart_clk_src_legacy_t

Type of UART clock source, reserved for the legacy UART driver.

Values:

enumerator UART_SCLK_APB: UART source clock is APB CLK

enumerator UART_SCLK_REF_TICK: UART source clock is REF_TICK

enumerator UART_SCLK_DEFAULT: UART source clock default choice is APB

enum soc_periph_mcpwm_timer_clk_src_t

Type of MCPWM timer clock source.

Values:

enumerator MCPWM_TIMER_CLK_SRC_PLL160M: Select PLL_F160M as the source clock

enumerator MCPWM_TIMER_CLK_SRC_DEFAULT: Select PLL_F160M as the default clock choice

enum soc_periph_mcpwm_capture_clk_src_t

Type of MCPWM capture clock source.

Values:

enumerator MCPWM_CAPTURE_CLK_SRC_APB: Select APB as the source clock

enumerator MCPWM_CAPTURE_CLK_SRC_DEFAULT: Select APB as the default clock choice

enum soc_periph_mcpwm_carrier_clk_src_t

Type of MCPWM carrier clock source.

Values:

enumerator MCPWM_CARRIER_CLK_SRC_PLL160M: Select PLL_F160M as the source clock

enumerator MCPWM_CARRIER_CLK_SRC_DEFAULT: Select PLL_F160M as the default clock choice

enum soc_periph_i2s_clk_src_t

I2S clock source enum.

Values:

enumerator I2S_CLK_SRC_DEFAULT: Select PLL_F160M as the default source clock

enumerator I2S_CLK_SRC_PLL_160M: Select PLL_F160M as the source clock

enumerator I2S_CLK_SRC_APLL: Select APLL as the source clock

enum soc_periph_i2c_clk_src_t

Type of I2C clock source.

Values:

enumerator I2C_CLK_SRC_APB

enumerator I2C_CLK_SRC_DEFAULT

enum soc_periph_spi_clk_src_t

Type of SPI clock source.

Values:

enumerator SPI_CLK_SRC_DEFAULT: Select APB as SPI source clock

enumerator SPI_CLK_SRC_APB: Select APB as SPI source clock

enum soc_periph_sdm_clk_src_t

Sigma Delta Modulator clock source.

Values:

enumerator SDM_CLK_SRC_APB: Select APB as the source clock

enumerator SDM_CLK_SRC_DEFAULT: Select APB as the default clock choice

enum soc_periph_dac_digi_clk_src_t

DAC digital controller clock source.

Values:

enumerator DAC_DIGI_CLK_SRC_PLLD2: Select PLL_D2 as the source clock

enumerator DAC_DIGI_CLK_SRC_APLL: Select APLL as the source clock

enumerator DAC_DIGI_CLK_SRC_DEFAULT: Select PLL_D2 as the default source clock

enum soc_periph_dac_cosine_clk_src_t

DAC cosine wave generator clock source.

Values:

enumerator DAC_COSINE_CLK_SRC_RTC_FAST: Select RTC FAST as the source clock

enumerator DAC_COSINE_CLK_SRC_DEFAULT: Select RTC FAST as the default source clock

enum soc_periph_twai_clk_src_t

TWAI clock source.

Values:

enumerator TWAI_CLK_SRC_APB: Select APB as the source clock

enumerator TWAI_CLK_SRC_DEFAULT: Select APB as the default clock choice

enum soc_periph_adc_digi_clk_src_t

ADC digital controller clock source.

备注

ADC DMA mode is clocked from I2S on ESP32, using ADC_DIGI_ here for compatibility Its clock source is same as I2S

Values:

enumerator ADC_DIGI_CLK_SRC_PLL_F160M: Select F160M as the source clock

enumerator ADC_DIGI_CLK_SRC_APLL: Select APLL as the source clock

enumerator ADC_DIGI_CLK_SRC_DEFAULT: Select F160M as the default clock choice

enum soc_periph_adc_rtc_clk_src_t

ADC RTC controller clock source.

Values:

enumerator ADC_RTC_CLK_SRC_RC_FAST: Select RC_FAST as the source clock

enumerator ADC_RTC_CLK_SRC_DEFAULT: Select RC_FAST as the default clock choice

enum soc_periph_mwdt_clk_src_t

MWDT clock source.

Values:

enumerator MWDT_CLK_SRC_APB: Select APB as the source clock

enumerator MWDT_CLK_SRC_DEFAULT: Select APB as the default clock choice

enum soc_periph_ledc_clk_src_legacy_t

Type of LEDC clock source, reserved for the legacy LEDC driver.

Values:

enumerator LEDC_AUTO_CLK: LEDC source clock will be automatically selected based on the giving resolution and duty parameter when init the timer

enumerator LEDC_USE_APB_CLK: Select APB as the source clock

enumerator LEDC_USE_RC_FAST_CLK: Select RC_FAST as the source clock

enumerator LEDC_USE_REF_TICK: Select REF_TICK as the source clock

enumerator LEDC_USE_RTC8M_CLK: Alias of 'LEDC_USE_RC_FAST_CLK'

Header File

components/esp_hw_support/include/esp_clk_tree.h

Functions

esp_err_t esp_clk_tree_src_get_freq_hz(soc_module_clk_t clk_src, esp_clk_tree_src_freq_precision_t precision, uint32_t *freq_value)

Get frequency of module clock source.

参数

clk_src -- [in] Clock source available to modules, in soc_module_clk_t
precision -- [in] Degree of precision, one of esp_clk_tree_src_freq_precision_t values This arg only applies to the clock sources that their frequencies can vary: SOC_MOD_CLK_RTC_FAST, SOC_MOD_CLK_RTC_SLOW, SOC_MOD_CLK_RC_FAST, SOC_MOD_CLK_RC_FAST_D256, SOC_MOD_CLK_XTAL32K For other clock sources, this field is ignored.
freq_value -- [out] Frequency of the clock source, in Hz

返回

ESP_OK Success
ESP_ERR_INVALID_ARG Parameter error
ESP_FAIL Calibration failed

Enumerations

enum esp_clk_tree_src_freq_precision_t

Degree of precision of frequency value to be returned by esp_clk_tree_src_get_freq_hz()

Values:

enumerator ESP_CLK_TREE_SRC_FREQ_PRECISION_CACHED

enumerator ESP_CLK_TREE_SRC_FREQ_PRECISION_APPROX

enumerator ESP_CLK_TREE_SRC_FREQ_PRECISION_EXACT

enumerator ESP_CLK_TREE_SRC_FREQ_PRECISION_INVALID

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