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docs: update the description for RTC Clock Sources for esp32 and esp32s2

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Wang Fang 2020-09-23 17:13:19 +08:00
parent 3c2f2aaffe
commit a50966cf7a
3 changed files with 17 additions and 14 deletions
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8
components/esp32/Kconfig
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@ -545,11 +545,11 @@ menu "ESP32-specific"
expense of slightly higher (1uA) deep sleep current consumption.
- "External 32kHz oscillator" allows using 32kHz clock generated by an
external circuit. In this case, external clock signal must be connected
to 32K_XP pin. Amplitude should be <1.2V in case of sine wave signal,
to 32K_XN pin. Amplitude should be <1.2V in case of sine wave signal,
and <1V in case of square wave signal. Common mode voltage should be
0.1 < Vcm < 0.5Vamp, where Vamp is the signal amplitude.
Additionally, 1nF capacitor must be connected between 32K_XN pin and
ground. 32K_XN pin can not be used as a GPIO in this case.
Additionally, 1nF capacitor must be connected between 32K_XP pin and
ground. 32K_XP pin can not be used as a GPIO in this case.
- "Internal 8.5MHz oscillator divided by 256" option results in higher
deep sleep current (by 5uA) but has better frequency stability than
the internal 150kHz oscillator. It does not require external components.
@ -560,7 +560,7 @@ menu "ESP32-specific"
bool "External 32kHz crystal"
select ESP_SYSTEM_RTC_EXT_XTAL
config ESP32_RTC_CLK_SRC_EXT_OSC
bool "External 32kHz oscillator at 32K_XP pin"
bool "External 32kHz oscillator at 32K_XN pin"
config ESP32_RTC_CLK_SRC_INT_8MD256
bool "Internal 8.5MHz oscillator, divided by 256 (~33kHz)"
endchoice

10
components/esp32s2/Kconfig
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@ -414,11 +414,11 @@ menu "ESP32S2-specific"
expense of slightly higher (1uA) deep sleep current consumption.
- "External 32kHz oscillator" allows using 32kHz clock generated by an
external circuit. In this case, external clock signal must be connected
to 32K_XP pin. Amplitude should be <1.2V in case of sine wave signal,
to 32K_XN pin. Amplitude should be <1.2V in case of sine wave signal,
and <1V in case of square wave signal. Common mode voltage should be
0.1 < Vcm < 0.5Vamp, where Vamp is the signal amplitude.
Additionally, 1nF capacitor must be connected between 32K_XN pin and
ground. 32K_XN pin can not be used as a GPIO in this case.
Additionally, 1nF capacitor must be connected between 32K_XP pin and
ground. 32K_XP pin can not be used as a GPIO in this case.
- "Internal 8MHz oscillator divided by 256" option results in higher
deep sleep current (by 5uA) but has better frequency stability than
the internal 90kHz oscillator. It does not require external components.
@ -429,7 +429,7 @@ menu "ESP32S2-specific"
bool "External 32kHz crystal"
select ESP_SYSTEM_RTC_EXT_XTAL
config ESP32S2_RTC_CLK_SRC_EXT_OSC
bool "External 32kHz oscillator at 32K_XP pin"
bool "External 32kHz oscillator at 32K_XN pin"
config ESP32S2_RTC_CLK_SRC_INT_8MD256
bool "Internal 8MHz oscillator, divided by 256 (~32kHz)"
endchoice
@ -450,7 +450,7 @@ menu "ESP32S2-specific"
When this option is set to 0, clock calibration will not be performed at
startup, and approximate clock frequencies will be assumed:
- 150000 Hz if internal RC oscillator is used as clock source. For this use value 1024.
- 90000 Hz if internal RC oscillator is used as clock source. For this use value 1024.
- 32768 Hz if the 32k crystal oscillator is used. For this use value 3000 or more.
In case more value will help improve the definition of the launch of the crystal.
If the crystal could not start, it will be switched to internal RC.

13
docs/en/api-reference/system/system_time.rst
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@ -1,6 +1,9 @@
System Time
===========
{IDF_TARGET_RTC_CLK_FRE:default="150kHz", esp32="150kHz", esp32s2="90kHz"}
{IDF_TARGET_HARDWARE_DESIGN_URL:default="`ESP32 Hardware Design Guidelines <https://www.espressif.com/sites/default/files/documentation/esp32_hardware_design_guidelines_en.pdf#page=10>`_", esp32="`ESP32 Hardware Design Guidelines <https://www.espressif.com/sites/default/files/documentation/esp32_hardware_design_guidelines_en.pdf#page=10>`_", esp32s2="`ESP32-S2 Hardware Design Guidelines <https://www.espressif.com/sites/default/files/documentation/esp32-s2_hardware_design_guidelines_en.pdf#page=10>`_"}
Overview
--------
@ -27,17 +30,17 @@ RTC Clock Source
The RTC timer has the following clock sources:
- ``Internal 150kHz RC oscillator`` (default): Features lowest deep sleep current consumption and no dependence on any external components. However, as frequency stability is affected by temperature fluctuations, time may drift in both Deep and Light sleep modes.
- ``Internal {IDF_TARGET_RTC_CLK_FRE} RC oscillator`` (default): Features lowest deep sleep current consumption and no dependence on any external components. However, as frequency stability is affected by temperature fluctuations, time may drift in both Deep and Light sleep modes.
- ``External 32kHz crystal``: Requires a 32kHz crystal to be connected to the 32K_XP and 32K_NP pins. Provides better frequency stability at the expense of slightly higher (by 1 uA) Deep sleep current consumption.
- ``External 32kHz crystal``: Requires a 32kHz crystal to be connected to the 32K_XP and 32K_XN pins. Provides better frequency stability at the expense of slightly higher (by 1 uA) Deep sleep current consumption.
- ``External 32kHz oscillator at 32K_XP pin``: Allows using 32kHz clock generated by an external circuit. The external clock signal must be connected to the 32K_XP pin. The amplitude should be less than 1.2 V for sine wave signal and less than 1 V for square wave signal. Common mode voltage should be in the range of 0.1 < Vcm < 0.5xVamp, where Vamp is signal amplitude. Additionally, a 1 nF capacitor must be placed between the 32K_XN pin and ground. In this case, the 32K_XN pin cannot be used as a GPIO pin.
- ``External 32kHz oscillator at 32K_XN pin``: Allows using 32kHz clock generated by an external circuit. The external clock signal must be connected to the 32K_XN pin. The amplitude should be less than 1.2 V for sine wave signal and less than 1 V for square wave signal. Common mode voltage should be in the range of 0.1 < Vcm < 0.5xVamp, where Vamp is signal amplitude. Additionally, a 1 nF capacitor must be placed between the 32K_XP pin and ground. In this case, the 32K_XP pin cannot be used as a GPIO pin.
- ``Internal 8.5MHz oscillator, divided by 256 (~33kHz)``. Provides better frequency stability than the ``internal 150kHz RC oscillator`` at the expense of higher (by 5 uA) deep sleep current consumption. It also does not require external components.
- ``Internal 8.5MHz oscillator, divided by 256 (~33kHz)``: Provides better frequency stability than the ``internal {IDF_TARGET_RTC_CLK_FRE} RC oscillator`` at the expense of higher (by 5 uA) deep sleep current consumption. It also does not require external components.
The choice depends on your requirements for system time accuracy and power consumption in sleep modes. To modify the RTC clock source, set :ref:`CONFIG_{IDF_TARGET_CFG_PREFIX}_RTC_CLK_SRC` in project configuration.
More details on wiring requirements for the ``External 32kHz crystal`` and ``External 32kHz oscillator at 32K_XP pin`` sources can be found in Section 2.1.4 *Crystal Oscillator* of `Hardware Design Guidelines <https://www.espressif.com/sites/default/files/documentation/esp32_hardware_design_guidelines_en.pdf#page=10>`_.
More details on wiring requirements for the ``External 32kHz crystal`` and ``External 32kHz oscillator at 32K_XN pin`` sources can be found in Section *Crystal Oscillator* of {IDF_TARGET_HARDWARE_DESIGN_URL}.
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