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espressif,esp32-pinctrl

Vendor: Espressif Systems

Description

Espressif's pin controller is in charge of controlling pin configurations, pin
functionalities and pin properties as defined by pin states. In its turn, pin
states are composed by groups of pre-defined pin muxing definitions and user
provided pin properties.

Each Zephyr-based application has its own set of pin muxing/pin configuration
requirements. The next steps use ESP-WROVER-KIT's I2C_0 to illustrate how one
could change a node's pin state properties. Though based on a particular board,
the same steps can be tweaked to address specifics of any other target board.

Suppose an application running on top of the ESP-WROVER-KIT board, for some
reason it needs I2C_0's SDA signal to be routed to GPIO_33. When looking at
that board's original device tree source file (i.e., 'esp_wrover_kit.dts'),
you'll notice that the I2C_0 node is already assigned to a pre-defined state.
Below is highlighted the information that most interests us on that file


    #include "esp_wrover_kit-pinctrl.dtsi"

    &i2c0 {
            ...
            pinctrl-0 = <&i2c0_default>;
            pinctrl-names = "default";
    };


From the above excerpt, the pincrl-0 property is assigned the 'i2c0_default'
state value. This and other pin states of the board are defined on another file
(in this case, 'esp_wrover_kit-pinctrl.dtsi') on the same folder of the DTS file.
Check below the excerpt describing I2C_0's default state on that file


    i2c0_default: i2c0_default {
            group1 {
                    pinmux = <I2C0_SDA_GPIO21>,
                             <I2C0_SCL_GPIO22>;
                    bias-pull-up;
                    drive-open-drain;
                    output-high;
            };
    };


Only the 'pinmux' property above is actually required, other properties can
be chosen if meaningful for the target application and, of course, supported
by your target hardware. For example, some custom board may have an external
pull-up resistor soldered to GPIO_21's pin pad, in which case, 'bias-pull-up'
could be no longer required.

Back to our fictional application, the previous I2C_0 state definition does not
meet our expectations as we would like to route I2C_0's SDA signal to GPIO_33
instead of to GPIO_21. To achieve it, we need to update the 'pinmux' property
accordingly.

Note that replacing 'I2C0_SDA_GPIO21' by 'I2C0_SDA_GPIO33' is very tempting and
may even work, however, unless you have checked the hardware documentation first,
it is not recommended. That's because there are no guarantees that a particular
IO pin has the capability to route any specific signal.

The recommendation is to check the pinmux macros definitions available for the
target SoC in the following URL


https://github.com/zephyrproject-rtos/hal_espressif/tree/zephyr/include/dt-bindings/pinctrl


The ESP-WROVER-KIT board is based on the ESP32 SoC, in that case, we search
through the file 'esp32-pinctrl.h' in the above URL. Luckily for us, there is
one definition on that file that corresponds to our needs


    #define I2C0_SDA_GPIO33 \
            ESP32_PINMUX(33, ESP_I2CEXT0_SDA_IN, ESP_I2CEXT0_SDA_OUT)


Now, we go back to edit 'esp_wrover_kit-pinctrl.dtsi' and create a new pin state
on that file (or replace/update the one already defined) using the pinmux macro
definition above, yielding


    i2c0_default: i2c0_default {
            group1 {
                    pinmux = <I2C0_SDA_GPIO33>,
                             <I2C0_SCL_GPIO22>;
                    bias-pull-up;
                    drive-open-drain;
                    output-high;
            };
    };


With proper modifications, the same steps above apply when using different
combinations of boards, SoCs, peripherals and peripheral pins.

Note: Not all pins are available for a given peripheral, it depends if that
      pin supports a set of properties required by the target peripheral.

      When defining a state, the pin muxing information is constrained to
      the definitions at 'hal_espressif', however, pin properties (like
      bias-push-pull, drive-open-drain, etc) can be freely chosen, given the
      property is meaningful to the peripheral signal and that it is also
      available in the target GPIO.

      Another thing worth noting is that all pin properties should be grouped.
      All pins sharing common properties go under a common group (in the above
      example, all pins are in 'group1'). Other peripherals can have more than
      one group.

Properties

Top level properties

These property descriptions apply to “espressif,esp32-pinctrl” nodes themselves. This page also describes child node properties in the following sections.

Properties not inherited from the base binding file.

(None)

Grandchild node properties

Name

Type

Details

pinmux

array

Each array element represents pin muxing information of an individual
pin. The array elements are pre-declared macros taken from Espressif's
HAL.

This property is required.

bias-disable

boolean

disable any pin bias

bias-pull-up

boolean

enable pull-up resistor

bias-pull-down

boolean

enable pull-down resistor

drive-push-pull

boolean

drive actively high and low

drive-open-drain

boolean

drive with open drain (hardware AND)

input-enable

boolean

enable input on pin (no effect on output, such as enabling an input
buffer)

output-enable

boolean

enable output on a pin without actively driving it (such as enabling
an output buffer)

output-low

boolean

set the pin to output mode with low level

output-high

boolean

set the pin to output mode with high level