| .. _pinctrl-guide: |
| |
| Pin Control |
| ########### |
| |
| This is a high-level guide to pin control. See :ref:`pinctrl_api` for API |
| reference material. |
| |
| Introduction |
| ************ |
| |
| The hardware blocks that control pin multiplexing and pin configuration |
| parameters such as pin direction, pull-up/down resistors, etc. are named **pin |
| controllers**. The pin controller's main users are SoC hardware peripherals, |
| since the controller enables exposing peripheral signals, like for example, |
| map ``I2C0`` ``SDA`` signal to pin ``PX0``. Not only that, but it usually allows |
| configuring certain pin settings that are necessary for the correct functioning |
| of a peripheral, for example, the slew-rate depending on the operating |
| frequency. The available configuration options are vendor/SoC dependent and can |
| range from simple pull-up/down options to more advanced settings such as |
| debouncing, low-power modes, etc. |
| |
| The way pin control is implemented in hardware is vendor/SoC specific. It is |
| common to find a *centralized* approach, that is, all pin configuration |
| parameters are controlled by a single hardware block (typically named pinmux), |
| including signal mapping. :numref:`pinctrl-hw-cent-control` illustrates this |
| approach. ``PX0`` can be mapped to ``UART0_TX``, ``I2C0_SCK`` or ``SPI0_MOSI`` |
| depending on the ``AF`` control bits. Other configuration parameters such as |
| pull-up/down are controlled in the same block via ``CONFIG`` bits. This model is |
| used by several SoC families, such as many from NXP and STM32. |
| |
| .. _pinctrl-hw-cent-control: |
| |
| .. figure:: images/hw-cent-control.svg |
| |
| Example of pin control centralized into a single per-pin block |
| |
| Other vendors/SoCs use a *distributed* approach. In such case, the pin mapping |
| and configuration are controlled by multiple hardware blocks. |
| :numref:`pinctrl-hw-dist-control` illustrates a distributed approach where pin |
| mapping is controlled by peripherals, such as in Nordic nRF SoCs. |
| |
| .. _pinctrl-hw-dist-control: |
| |
| .. figure:: images/hw-dist-control.svg |
| |
| Example pin control distributed between peripheral registers and per-pin block |
| |
| From a user perspective, there is no difference in pin controller usage |
| regardless of the hardware implementation: a user will always apply a state. |
| The only difference lies in the driver implementation. In general, implementing |
| a pin controller driver for a hardware that uses a distributed approach requires |
| more effort, since the driver needs to gather knowledge of peripheral dependent |
| registers. |
| |
| Pin control vs. GPIO |
| ==================== |
| |
| Some functionality covered by a pin controller driver overlaps with GPIO |
| drivers. For example, pull-up/down resistors can usually be enabled by both the |
| pin control driver and the GPIO driver. In Zephyr context, the pin control |
| driver purpose is to perform peripheral signal multiplexing and configuration of |
| other pin parameters required for the correct operation of that peripheral. |
| Therefore, the main users of the pin control driver are SoC peripherals. In |
| contrast, GPIO drivers are for general purpose control of a pin, that is, when |
| its logic level is read or controlled manually. |
| |
| State model |
| *********** |
| |
| For a device driver to operate correctly, a certain pin configuration needs to |
| be applied. Some device drivers require a static configuration, usually set up |
| at initialization time. Others need to change the configuration at runtime |
| depending on the operating conditions, for example, to enable a low-power mode |
| when suspending the device. Such requirements are modeled using **states**, a |
| concept that has been adapted from the one in the Linux kernel. Each device |
| driver owns a set of states. Each state has a unique name and contains a full |
| pin configuration set (see :numref:`pinctrl-states-model`). This effectively |
| means that states are independent of each other, so they do not need to be |
| applied in any specific order. Another advantage of the state model is that it |
| isolates device drivers from pin configuration. |
| |
| .. _pinctrl-states-model: |
| |
| .. table:: Example pin configuration encoded using the states model |
| :align: center |
| |
| +----+------------------+----+------------------+ |
| | ``UART0`` peripheral | |
| +====+==================+====+==================+ |
| | ``default`` state | ``sleep`` state | |
| +----+------------------+----+------------------+ |
| | TX | - Pin: PA0 | TX | - Pin: PA0 | |
| | | - Pull: NONE | | - Pull: NONE | |
| | | - Low Power: NO | | - Low Power: YES | |
| +----+------------------+----+------------------+ |
| | RX | - Pin: PA1 | RX | - Pin: PA1 | |
| | | - Pull: UP | | - Pull: NONE | |
| | | - Low Power: NO | | - Low Power: YES | |
| +----+------------------+----+------------------+ |
| |
| Standard states |
| =============== |
| |
| The name assigned to pin control states or the number of them is up to the |
| device driver requirements. In many cases a single state applied at |
| initialization time will be sufficient, but in some other cases more will be |
| required. In order to make things consistent, a naming convention has been |
| established for the most common use cases. :numref:`pinctrl-states-standard` |
| details the standardized states and its purpose. |
| |
| .. _pinctrl-states-standard: |
| |
| .. table:: Standardized state names |
| :align: center |
| |
| +-------------+----------------------------------+-------------------------+ |
| | State | Identifier | Purpose | |
| +-------------+----------------------------------+-------------------------+ |
| | ``default`` | :c:macro:`PINCTRL_STATE_DEFAULT` | State of the pins when | |
| | | | the device is in | |
| | | | operational state | |
| +-------------+----------------------------------+-------------------------+ |
| | ``sleep`` | :c:macro:`PINCTRL_STATE_SLEEP` | State of the pins when | |
| | | | the device is in low | |
| | | | power or sleep modes | |
| +-------------+----------------------------------+-------------------------+ |
| |
| Note that other standard states could be introduced in the future. |
| |
| Custom states |
| ============= |
| |
| Some device drivers may require using custom states beyond the standard ones. To |
| achieve that, the device driver needs to have in its scope definitions for the |
| custom state identifiers named as ``PINCTRL_STATE_{STATE_NAME}``, where |
| ``{STATE_NAME}`` is the capitalized state name. For example, if ``mystate`` has |
| to be supported, a definition named ``PINCTRL_STATE_MYSTATE`` needs to be |
| in the driver's scope. |
| |
| .. note:: |
| It is important that custom state identifiers start from |
| :c:macro:`PINCTRL_STATE_PRIV_START` |
| |
| If custom states need to be accessed from outside the driver, for example to |
| perform dynamic pin control, custom identifiers should be placed in a header |
| that is publicly accessible. |
| |
| Skipping states |
| =============== |
| |
| In most situations, the states defined in Devicetree will be the ones used in |
| the compiled firmware. However, there are some cases where certain states will |
| be conditionally used depending on a compilation flag. A typical case is the |
| ``sleep`` state. This state is only used in practice if |
| :kconfig:option:`CONFIG_PM_DEVICE` is enabled. If a firmware variant without device |
| power management is needed, one should in theory remove the ``sleep`` state from |
| Devicetree to not waste ROM space storing such unused state. |
| |
| States can be skipped by the ``pinctrl`` Devicetree macros if a definition named |
| ``PINCTRL_SKIP_{STATE_NAME}`` expanding to ``1`` is present when pin control |
| configuration is defined. In case of the ``sleep`` state, the ``pinctrl`` API |
| already provides such definition conditional to the availability of device power |
| management: |
| |
| .. code-block:: c |
| |
| #ifndef CONFIG_PM_DEVICE |
| /** If device power management is not enabled, "sleep" state will be ignored. */ |
| #define PINCTRL_SKIP_SLEEP 1 |
| #endif |
| |
| Dynamic pin control |
| ******************* |
| |
| Dynamic pin control refers to the capability of changing pin configuration |
| at runtime. This feature can be useful in situations where the same firmware |
| needs to run onto slightly different boards, each having a peripheral routed at |
| a different set of pins. This feature can be enabled by setting |
| :kconfig:option:`CONFIG_PINCTRL_DYNAMIC`. |
| |
| .. note:: |
| |
| Dynamic pin control should only be used on devices that have not been |
| initialized. Changing pin configurations while a device is operating may |
| lead to unexpected behavior. Since Zephyr does not support device |
| de-initialization yet, this functionality should only be used during early |
| boot stages. |
| |
| One of the effects of enabling dynamic pin control is that |
| :c:struct:`pinctrl_dev_config` will be stored in RAM instead of ROM (not states |
| or pin configurations, though). The user can then use |
| :c:func:`pinctrl_update_states` to update the states stored in |
| :c:struct:`pinctrl_dev_config` with a new set. This effectively means that the |
| device driver will apply the pin configurations stored in the updated states |
| when it applies a state. |
| |
| Devicetree representation |
| ************************* |
| |
| Because Devicetree is meant to describe hardware, it is the natural choice when |
| it comes to storing pin control configuration. In the following sections you |
| will find an overview on how states and pin configurations are represented in |
| Devicetree. |
| |
| States |
| ====== |
| |
| Given a device, each of its pin control state is represented in Devicetree by |
| ``pinctrl-N`` properties, being ``N`` the state index starting from zero. The |
| ``pinctrl-names`` property is then used to assign a unique identifier for each |
| state property by index, for example, ``pinctrl-names`` list entry 0 is the name |
| for ``pinctrl-0``. |
| |
| .. code-block:: devicetree |
| |
| periph0: periph@0 { |
| ... |
| /* state 0 ("default") */ |
| pinctrl-0 = <...>; |
| ... |
| /* state N ("mystate") */ |
| pinctrl-N = <...>; |
| /* names for state 0 up to state N */ |
| pinctrl-names = "default", ..., "mystate"; |
| ... |
| }; |
| |
| Pin configuration |
| ================= |
| |
| There are multiple ways to represent the pin configurations in Devicetree. |
| However, all end up encoding the same information: the pin multiplexing and the |
| pin configuration parameters. For example, ``UART_RX`` is mapped to ``PX0`` and |
| pull-up is enabled. The representation choice largely depends on each |
| vendor/SoC, so the Devicetree binding files for the pin control drivers are the |
| best place to look for details. |
| |
| A popular and versatile option is shown in the example below. One of the |
| advantages of this choice is the grouping capability based on shared pin |
| configuration. This allows to reduce the verbosity of the pin control |
| definitions. Another advantage is that the pin configuration parameters for a |
| particular state are enclosed in a single Devicetree node. |
| |
| .. code-block:: devicetree |
| |
| /* board.dts */ |
| #include "board-pinctrl.dtsi" |
| |
| &periph0 { |
| pinctrl-0 = <&periph0_default>; |
| pinctrl-names = "default"; |
| }; |
| |
| .. code-block:: c |
| |
| /* vnd-soc-pkgxx.h |
| * File with valid mappings for a specific package (may be autogenerated). |
| * This file is optional, but recommended. |
| */ |
| ... |
| #define PERIPH0_SIGA_PX0 VNDSOC_PIN(X, 0, MUX0) |
| #define PERIPH0_SIGB_PY7 VNDSOC_PIN(Y, 7, MUX4) |
| #define PERIPH0_SIGC_PZ1 VNDSOC_PIN(Z, 1, MUX2) |
| ... |
| |
| .. code-block:: devicetree |
| |
| /* board-pinctrl.dtsi */ |
| #include <vnd-soc-pkgxx.h> |
| |
| &pinctrl { |
| /* Node with pin configuration for default state */ |
| periph0_default: periph0_default { |
| group1 { |
| /* Mappings: PERIPH0_SIGA -> PX0, PERIPH0_SIGC -> PZ1 */ |
| pinmux = <PERIPH0_SIGA_PX0>, <PERIPH0_SIGC_PZ1>; |
| /* Pins PX0 and PZ1 have pull-up enabled */ |
| bias-pull-up; |
| }; |
| ... |
| groupN { |
| /* Mappings: PERIPH0_SIGB -> PY7 */ |
| pinmux = <PERIPH0_SIGB_PY7>; |
| }; |
| }; |
| }; |
| |
| Another popular model is based on having a node for each pin configuration and |
| state. While this model may lead to shorter board pin control files, it also |
| requires to have one node for each pin mapping and state, since in general, |
| nodes can not be re-used for multiple states. This method is discouraged if |
| autogeneration is not an option. |
| |
| .. note:: |
| |
| Because all Devicetree information is parsed into a C header, it is important |
| to make sure its size is kept to a minimum. For this reason it is important |
| to prefix pre-generated nodes with ``/omit-if-no-ref/``. This prefix makes |
| sure that the node is discarded when not used. |
| |
| .. code-block:: devicetree |
| |
| /* board.dts */ |
| #include "board-pinctrl.dtsi" |
| |
| &periph0 { |
| pinctrl-0 = <&periph0_siga_px0_default &periph0_sigb_py7_default |
| &periph0_sigc_pz1_default>; |
| pinctrl-names = "default"; |
| }; |
| |
| .. code-block:: devicetree |
| |
| /* vnd-soc-pkgxx.dtsi |
| * File with valid nodes for a specific package (may be autogenerated). |
| * This file is optional, but recommended. |
| */ |
| |
| &pinctrl { |
| /* Mapping for PERIPH0_SIGA -> PX0, to be used for default state */ |
| /omit-if-no-ref/ periph0_siga_px0_default: periph0_siga_px0_default { |
| pinmux = <VNDSOC_PIN(X, 0, MUX0)>; |
| }; |
| |
| /* Mapping for PERIPH0_SIGB -> PY7, to be used for default state */ |
| /omit-if-no-ref/ periph0_sigb_py7_default: periph0_sigb_py7_default { |
| pinmux = <VNDSOC_PIN(Y, 7, MUX4)>; |
| }; |
| |
| /* Mapping for PERIPH0_SIGC -> PZ1, to be used for default state */ |
| /omit-if-no-ref/ periph0_sigc_pz1_default: periph0_sigc_pz1_default { |
| pinmux = <VNDSOC_PIN(Z, 1, MUX2)>; |
| }; |
| }; |
| |
| .. code-block:: devicetree |
| |
| /* board-pinctrl.dts */ |
| #include <vnd-soc-pkgxx.dtsi> |
| |
| /* Enable pull-up for PX0 (default state) */ |
| &periph0_siga_px0_default { |
| bias-pull-up; |
| }; |
| |
| /* Enable pull-up for PZ1 (default state) */ |
| &periph0_sigc_pz1_default { |
| bias-pull-up; |
| }; |
| |
| .. note:: |
| |
| It is discouraged to add pin configuration defaults in pre-defined nodes. |
| In general, pin configurations depend on the board design or on the |
| peripheral working conditions, so the decision should be made by the board. |
| For example, enabling a pull-up by default may not always be desired because |
| the board already has one or because its value depends on the operating bus |
| speed. Another downside of defaults is that user may not be aware of them, |
| for example: |
| |
| .. code-block:: devicetree |
| |
| /* not evident that "periph0_siga_px0_default" also implies "bias-pull-up" */ |
| /omit-if-no-ref/ periph0_siga_px0_default: periph0_siga_px0_default { |
| pinmux = <VNDSOC_PIN(X, 0, MUX0)>; |
| bias-pull-up; |
| }; |
| |
| Implementation guidelines |
| ************************* |
| |
| Pin control drivers |
| =================== |
| |
| Pin control drivers need to implement a single function: |
| :c:func:`pinctrl_configure_pins`. This function receives an array of pin |
| configurations that need to be applied. Furthermore, if |
| :kconfig:option:`CONFIG_PINCTRL_STORE_REG` is set, it also receives the associated |
| device register address for the given pins. This information may be required by |
| some drivers to perform device specific actions. |
| |
| The pin configuration is stored in an opaque type that is vendor/SoC dependent: |
| ``pinctrl_soc_pin_t``. This type needs to be defined in a header named |
| ``pinctrl_soc.h`` file that is in the Zephyr's include path. It can range from |
| a simple integer value to a struct with multiple fields. ``pinctrl_soc.h`` also |
| needs to define a macro named ``Z_PINCTRL_STATE_PINS_INIT`` that accepts two |
| arguments: a node identifier and a property name (``pinctrl-N``). With this |
| information the macro needs to define an initializer for all pin configurations |
| contained within the ``pinctrl-N`` property of the given node. |
| |
| Regarding Devicetree pin configuration representation, vendors can decide which |
| option is better for their devices. However, the following guidelines should be |
| followed: |
| |
| - Use ``pinctrl-N`` (N=0, 1, ...) and ``pinctrl-names`` properties to define pin |
| control states. These properties are defined in |
| :file:`dts/bindings/pinctrl/pinctrl-device.yaml`. |
| - Use standard pin configuration properties as defined in |
| :file:`dts/bindings/pinctrl/pincfg-node.yaml` or |
| :file:`dts/bindings/pinctrl/pincfg-node-group.yaml`. |
| |
| Representations not following these guidelines may be accepted if they are |
| already used by the same vendor in other operating systems, e.g. Linux. |
| |
| Device drivers |
| ============== |
| |
| In this section you will find some tips on how a device driver should use the |
| ``pinctrl`` API to successfully configure the pins it needs. |
| |
| The device compatible needs to be modified in the corresponding binding so that |
| the ``pinctrl-device.yaml`` is included. For example: |
| |
| .. code-block:: yaml |
| |
| include: [base.yaml, pinctrl-device.yaml] |
| |
| This file is needed to add ``pinctrl-N`` and ``pinctrl-names`` properties to the |
| device. |
| |
| From a device driver perspective there are two steps that need to be performed |
| to be able to use the ``pinctrl`` API. First, the pin control configuration |
| needs to be defined. This includes all states and pins. |
| :c:macro:`PINCTRL_DT_DEFINE` or :c:macro:`PINCTRL_DT_INST_DEFINE` macros |
| should be used for this purpose. Second, a reference to |
| the device instance :c:struct:`pinctrl_dev_config` needs to be stored, since it |
| is required to later use the API. This can be achieved using the |
| :c:macro:`PINCTRL_DT_DEV_CONFIG_GET` and |
| :c:macro:`PINCTRL_DT_INST_DEV_CONFIG_GET` macros. |
| |
| It is worth to note that the only relationship between a device and its |
| associated pin control configuration is based on variable naming conventions. |
| The way an instance of :c:struct:`pinctrl_dev_config` is named for a |
| corresponding device instance allows to later obtain a reference to it given the |
| device's Devicetree node identifier. This allows to minimize ROM usage, since |
| only devices requiring pin control will own a reference to a pin control |
| configuration. |
| |
| Once the driver has defined the pin control configuration and kept a reference |
| to it, it is ready to use the API. The most common way to apply a state is by |
| using :c:func:`pinctrl_apply_state`. It is also possible to use the lower level |
| function :c:func:`pinctrl_apply_state_direct` to skip state lookup if it is |
| cached in advance (e.g. at init time). Since state lookup time is expected to be |
| fast, it is recommended to use :c:func:`pinctrl_apply_state`. |
| |
| The example below contains a complete example of a device driver that uses the |
| ``pinctrl`` API. |
| |
| .. code-block:: c |
| |
| /* A driver for the "mydev" compatible device */ |
| #define DT_DRV_COMPAT mydev |
| |
| ... |
| #include <zephyr/drivers/pinctrl.h> |
| ... |
| |
| struct mydev_config { |
| ... |
| /* Reference to mydev pinctrl configuration */ |
| const struct pinctrl_dev_config *pcfg; |
| ... |
| }; |
| |
| ... |
| |
| static int mydev_init(const struct device *dev) |
| { |
| const struct mydev_config *config = dev->config; |
| int ret; |
| ... |
| /* Select "default" state at initialization time */ |
| ret = pinctrl_apply_state(config->pcfg, PINCTRL_STATE_DEFAULT); |
| if (ret < 0) { |
| return ret; |
| } |
| ... |
| } |
| |
| #define MYDEV_DEFINE(i) \ |
| /* Define all pinctrl configuration for instance "i" */ \ |
| PINCTRL_DT_INST_DEFINE(i); \ |
| ... \ |
| static const struct mydev_config mydev_config_##i = { \ |
| ... \ |
| /* Keep a ref. to the pinctrl configuration for instance "i" */ \ |
| .pcfg = PINCTRL_DT_INST_DEV_CONFIG_GET(i), \ |
| ... \ |
| }; \ |
| ... \ |
| \ |
| DEVICE_DT_INST_DEFINE(i, mydev_init, NULL, &mydev_data##i, \ |
| &mydev_config##i, ...); |
| |
| DT_INST_FOREACH_STATUS_OKAY(MYDEV_DEFINE) |
| |
| .. _pinctrl_api: |
| |
| Pin Control API |
| **************** |
| |
| .. doxygengroup:: pinctrl_interface |
| |
| Dynamic pin control |
| ==================== |
| |
| .. doxygengroup:: pinctrl_interface_dynamic |
| |
| |
| Other reference material |
| ************************ |
| |
| - `Introduction to pin muxing and GPIO control under Linux <https://static.sched.com/hosted_files/osselc21/b6/ELC-2021_Introduction_to_pin_muxing_and_GPIO_control_under_Linux.pdf>`_ |
