> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/wokwi/wokwi-docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Attributes

> Define configurable parameters for custom chips that users can set in diagram.json

Attributes are input parameters that the user can set in `diagram.json`. You can also define a [`controls` section](./chip-json#controls) in the `.chip.json` file to let the user edit these parameters interactively during the simulation. This is particularly useful for sensor inputs (e.g. temperature, humidity, etc.).

## Naming

When naming your attributes, please follow the following conventions:

* Use `camelCase` for attribute names
* Use American English spelling (e.g. `color` and not `colour`)

## attr\_init

```c theme={null}
uint32_t attr_init(const char *name, uint32_t default_value)
```

Defines a new integer attribute with the given name. The `default_value` will be used when the user does not define a value for the attribute in `diagram.json` (under the `attrs` section of the custom chip `part`).

The function returns a handle to the attribute, which can be accessed using `attr_read()`.

<Warning>
  Note: `attr_init` can only be called from `chip_init()`. Do not call it at a later time.
</Warning>

## attr\_init\_float

```c theme={null}
uint32_t attr_init_float(const char *name, float default_value)
```

Defines a new floating point attribute with the given name. See `attr_init()` for more info.

<Warning>
  Note: `attr_init_float` can only be called from `chip_init()`. Do not call it at a later time.
</Warning>

## attr\_read

```c theme={null}
uint32_t attr_read(uint32_t attr)
```

Returns the current value of the attribute. `attr` should be a valid attribute handle, previously returned by `attr_init()`.

## attr\_read\_float

```c theme={null}
float attr_read_float(uint32_t attr)
```

Returns the current value of the attribute. `attr` should be a valid attribute handle, previously returned by `attr_init_float()`.

## Simulator Examples

* [Analog API chip example](https://wokwi.com/projects/330112801381024338) -- Simulates a 0-5V/0-ADC\_MAX voltage source. One float attribute and one analog output.
* [PWM with Scope](https://wokwi.com/projects/354488725362438145) ([github](https://github.com/Dlloydev/Wokwi-Chip-PWM)) -- simulates a PWM input with 1 digital output and three attributes
* [Scope with PWM](https://wokwi.com/projects/354488725362438145) ([Scope with muliple inputs](https://wokwi.com/projects/359330496025635841)) ([github](https://github.com/Dlloydev/Wokwi-Chip-Scope)) -- Simulates a 4-channel oscilloscope with 4 digital inputs, 4 analog inputs and 4 attributes