:orphan:
.. raw:: html
.. dtcompatible:: st,stm32-rcc
.. _dtbinding_st_stm32_rcc:
st,stm32-rcc
############
Vendor: :ref:`STMicroelectronics N.V. `
Description
***********
.. code-block:: none
STM32 RCC (Reset and Clock controller).
This node is in charge of system clock ('SYSCLK') source selection and controlling
clocks for AHB (Advanced High Performance) and APB (Advanced Peripheral) bus domains.
Configuring STM32 Reset and Clock controller node:
System clock source should be selected amongst the clock nodes available in "clocks"
node (typically 'clk_hse, clk_hsi', 'pll', ...).
Core clock frequency should also be defined, using "clock-frequency" property.
Note:
Core clock frequency = SYSCLK / AHB prescaler
Last, peripheral bus clocks (typically PCLK1, PCLK2) should be configured using matching
prescaler properties.
Here is an example of correctly configured rcc node:
&rcc {
clocks = <&pll>; /* Select 80MHz pll as SYSCLK source */
ahb-prescaler = <2>;
clock-frequency = ; /* = SYSCLK / AHB prescaler */
apb1-prescaler = <1>;
apb2-prescaler = <1>;
}
Specifying a gated clock:
To specify a gated clock, a peripheral should define a "clocks" property encoded
in the following way:
... {
...
clocks = <&rcc STM32_CLOCK_BUS_APB2 0x00000020>;
...
}
After the phandle referring to rcc node, the first index specifies the registers of
the bus controlling the peripheral and the second index specifies the bit used to
control the peripheral clock in that bus register.
The gated clock is required when accessing to the peripheral controller is needed
(generally for configuring the device). If dual clock domain is not used, it is
also used for peripheral operation.
Specifying a domain clock source:
Specifying a domain source clock could be done by adding a clock specifier to the
clock property:
... {
...
clocks = <&rcc STM32_CLOCK_BUS_APB2 0x00000020>,
<&rcc STM32_SRC_HSI I2C1_SEL(2)>;
...
}
In this example, I2C1 device is assigned HSI as domain clock source.
Domain clock is independent from the bus/gated clock and allows access to the device's
register while the gated clock is off. As it doesn't feed the peripheral's controller, it
allows peripheral operation, but can't be used for peripheral configuration.
It is peripheral driver's responsibility to query and use clock source information in
accordance with clock_control API specifications.
Since the peripheral subsystem rate is dictated by the clock used for peripheral
operation, same clock should be used in calls to `clock_control_get_rate()`
Note 1: No additional specifier means gating clock is also the clock source (ie
'PCLK/PCLK1/PCLK2' depending on the device). There is no need to add a second
cell to explicitly set it.
Note 2: Default peripheral clock configuration (ie the one provided in *.dsti files)
should be the one matching SoC reset state. Confere reference manual to check
what is the reset value of the clock source for each peripheral.
Specifying a divided domain clock source:
Some peripherals are sourced through fixed clock dividers. For such cases there is
STM32_CLOCK_DIV() macro, which allows to specify such divider value. Selecting HSE/2 (HSE
frequency divided by 2) is done with following clock property:
... {
...
clocks = <&rcc (STM32_SRC_HSE | STM32_CLOCK_DIV(2)) ...>;
...
}
Properties
**********
.. tabs::
.. group-tab:: Node specific properties
Properties not inherited from the base binding file.
.. list-table::
:widths: 1 1 4
:header-rows: 1
* - Name
- Type
- Details
* - ``#clock-cells``
- ``int``
- .. code-block:: none
Number of items to expect in a Clock specifier
This property is **required**.
Constant value: ``2``
* - ``clock-frequency``
- ``int``
- .. code-block:: none
default frequency in Hz for clock output
This property is **required**.
* - ``ahb-prescaler``
- ``int``
- .. code-block:: none
AHB prescaler. Defines actual core clock frequency (HCLK)
based on system frequency input.
The HCLK clocks CPU, AHB, memories and DMA.
This property is **required**.
Legal values: ``1``, ``2``, ``4``, ``8``, ``16``, ``64``, ``128``, ``256``, ``512``
* - ``apb1-prescaler``
- ``int``
- This property is **required**.
Legal values: ``1``, ``2``, ``4``, ``8``, ``16``
* - ``apb2-prescaler``
- ``int``
- This property is **required**.
Legal values: ``1``, ``2``, ``4``, ``8``, ``16``
* - ``undershoot-prevention``
- ``boolean``
- .. code-block:: none
On some parts, it could be required to set up highest core frequencies
(>80MHz) in two steps in order to prevent undershoot.
This is done by applying an intermediate AHB prescaler before switching
System Clock source to PLL. Once done, prescaler is set back to expected
value.
.. group-tab:: Deprecated node specific properties
Deprecated properties not inherited from the base binding file.
(None)
.. group-tab:: Base properties
Properties inherited from the base binding file, which defines
common properties that may be set on many nodes. Not all of these
may apply to the "st,stm32-rcc" compatible.
.. list-table::
:widths: 1 1 4
:header-rows: 1
* - Name
- Type
- Details
* - ``reg``
- ``array``
- .. code-block:: none
Information used to address the device. The value is specific to
the device (i.e. is different depending on the compatible
property).
The "reg" property is typically a sequence of (address, length) pairs.
Each pair is called a "register block". Values are
conventionally written in hex.
For details, see "2.3.6 reg" in Devicetree Specification v0.4.
This property is **required**.
See :ref:`zephyr:dt-important-props` for more information.
* - ``status``
- ``string``
- .. code-block:: none
Indicates the operational status of the hardware or other
resource that the node represents. In particular:
- "okay" means the resource is operational and, for example,
can be used by device drivers
- "disabled" means the resource is not operational and the system
should treat it as if it is not present
For details, see "2.3.4 status" in Devicetree Specification v0.4.
Legal values: ``'ok'``, ``'okay'``, ``'disabled'``, ``'reserved'``, ``'fail'``, ``'fail-sss'``
See :ref:`zephyr:dt-important-props` for more information.
* - ``compatible``
- ``string-array``
- .. code-block:: none
This property is a list of strings that essentially define what
type of hardware or other resource this devicetree node
represents. Each device driver checks for specific compatible
property values to find the devicetree nodes that represent
resources that the driver should manage.
The recommended format is "vendor,device", The "vendor" part is
an abbreviated name of the vendor. The "device" is usually from
the datasheet.
The compatible property can have multiple values, ordered from
most- to least-specific. Having additional values is useful when the
device is a specific instance of a more general family, to allow the
system to match the most specific driver available.
For details, see "2.3.1 compatible" in Devicetree Specification v0.4.
This property is **required**.
See :ref:`zephyr:dt-important-props` for more information.
* - ``reg-names``
- ``string-array``
- .. code-block:: none
Optional names given to each register block in the "reg" property.
For example:
/ {
soc {
#address-cells = <1>;
#size-cells = <1>;
uart@1000 {
reg = <0x1000 0x2000>, <0x3000 0x4000>;
reg-names = "foo", "bar";
};
};
};
The uart@1000 node has two register blocks:
- one with base address 0x1000, size 0x2000, and name "foo"
- another with base address 0x3000, size 0x4000, and name "bar"
* - ``interrupts``
- ``array``
- .. code-block:: none
Information about interrupts generated by the device, encoded as an array
of one or more interrupt specifiers. The format of the data in this property
varies by where the device appears in the interrupt tree. Devices with the same
"interrupt-parent" will use the same format in their interrupts properties.
For details, see "2.4 Interrupts and Interrupt Mapping" in
Devicetree Specification v0.4.
See :ref:`zephyr:dt-important-props` for more information.
* - ``interrupts-extended``
- ``compound``
- .. code-block:: none
Extended interrupt specifier for device, used as an alternative to
the "interrupts" property.
For details, see "2.4 Interrupts and Interrupt Mapping" in
Devicetree Specification v0.4.
* - ``interrupt-names``
- ``string-array``
- .. code-block:: none
Optional names given to each interrupt generated by a device.
The interrupts themselves are defined in either "interrupts" or
"interrupts-extended" properties.
For details, see "2.4 Interrupts and Interrupt Mapping" in
Devicetree Specification v0.4.
* - ``interrupt-parent``
- ``phandle``
- .. code-block:: none
If present, this refers to the node which handles interrupts generated
by this device.
For details, see "2.4 Interrupts and Interrupt Mapping" in
Devicetree Specification v0.4.
* - ``label``
- ``string``
- .. code-block:: none
Human readable string describing the device. Use of this property is
deprecated except as needed on a case-by-case basis.
For details, see "4.1.2 Miscellaneous Properties" in Devicetree
Specification v0.4.
See :ref:`zephyr:dt-important-props` for more information.
* - ``clocks``
- ``phandle-array``
- .. code-block:: none
Information about the device's clock providers. In general, this property
should follow conventions established in the dt-schema binding:
https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml
* - ``clock-names``
- ``string-array``
- .. code-block:: none
Optional names given to each clock provider in the "clocks" property.
* - ``#address-cells``
- ``int``
- .. code-block:: none
This property encodes the number of cells used by address fields
in "reg" properties in this node's children.
For details, see "2.3.5 #address-cells and #size-cells" in Devicetree
Specification v0.4.
* - ``#size-cells``
- ``int``
- .. code-block:: none
This property encodes the number of cells used by size fields in
"reg" properties in this node's children.
For details, see "2.3.5 #address-cells and #size-cells" in Devicetree
Specification v0.4.
* - ``dmas``
- ``phandle-array``
- .. code-block:: none
DMA channel specifiers relevant to the device.
* - ``dma-names``
- ``string-array``
- .. code-block:: none
Optional names given to the DMA channel specifiers in the "dmas" property.
* - ``io-channels``
- ``phandle-array``
- .. code-block:: none
IO channel specifiers relevant to the device.
* - ``io-channel-names``
- ``string-array``
- .. code-block:: none
Optional names given to the IO channel specifiers in the "io-channels" property.
* - ``mboxes``
- ``phandle-array``
- .. code-block:: none
Mailbox / IPM channel specifiers relevant to the device.
* - ``mbox-names``
- ``string-array``
- .. code-block:: none
Optional names given to the mbox specifiers in the "mboxes" property.
* - ``power-domains``
- ``phandle-array``
- .. code-block:: none
Power domain specifiers relevant to the device.
* - ``power-domain-names``
- ``string-array``
- .. code-block:: none
Optional names given to the power domain specifiers in the "power-domains" property.
* - ``#power-domain-cells``
- ``int``
- .. code-block:: none
Number of cells in power-domains property
* - ``zephyr,deferred-init``
- ``boolean``
- .. code-block:: none
Do not initialize device automatically on boot. Device should be manually
initialized using device_init().
* - ``wakeup-source``
- ``boolean``
- .. code-block:: none
Property to identify that a device can be used as wake up source.
When this property is provided a specific flag is set into the
device that tells the system that the device is capable of
wake up the system.
Wake up capable devices are disabled (interruptions will not wake up
the system) by default but they can be enabled at runtime if necessary.
* - ``zephyr,pm-device-runtime-auto``
- ``boolean``
- .. code-block:: none
Automatically configure the device for runtime power management after the
init function runs.
* - ``zephyr,disabling-power-states``
- ``phandles``
- .. code-block:: none
List of power states that will disable this device power.
Specifier cell names
********************
- clock cells: bus, bits