Interfacing via Serial/UART

We have an example, minimal UART-based component.

Let’s take a closer look at this example.

Python

In addition to the usual requisite imports, we have:

from esphome.components import uart

This allows us to use some functions we’ll need for validation and code generation later on.

DEPENDENCIES = ["uart"]

Given that this component will use—and consequently depend on—a UART, we must add it as a dependency. This allows ESPHome to understand this requirement and generate an error if it is not met.

empty_uart_component_ns = cg.esphome_ns.namespace("empty_uart_component")
EmptyUARTComponent = empty_uart_component_ns.class_(
    "EmptyUARTComponent", cg.Component, uart.UARTDevice
)

This is some boilerplate code which allows ESPHome code generation to understand the namespace and class names that the component will use. Note that EmptyUARTComponent is inheriting from both Component and UARTDevice.

CONFIG_SCHEMA = ...

This defines the configuration schema for the component as discussed in Configuration validation. In particular, note that the schema is extended with .extend(uart.UART_DEVICE_SCHEMA) since this is a UART component/platform.

Finally, in the to_code function, we have:

await uart.register_uart_device(var, config)

Since this is a serial device which uses a UART, we must register it as such so it is handled appropriately by ESPHome.

C++

The C++ class for this example component is quite simple.

class EmptyUARTComponent : public uart::UARTDevice, public Component { ... };

As mentioned in the codebase standards, all components/platforms must inherit from either Component or PollingComponent; our example here is no different. Note that, since it’s a UART device, it also inherits from UARTDevice.

Finally, the component implements the usual set of methods as described here. This is all that’s required for our minimal UART component!