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Commit 81383a7b authored by Harry Cutts's avatar Harry Cutts
Browse files

uinput: tidy up the README 

The main changes are:

* Describe how multiple commands are passed to `uinput`
* Split details about waiting after device registration into its own
  section
* Add details on the JSON extensions `uinput` uses
* Change example code blocks to JSON5 syntax to better accommodate the
  JSON extensions
* Use absolute links to Android Codesearch instead of relative ones
* Fix various Markdown issues and improve formatting

Bug: 280604085
Test: check rendering in Google Markdown
Change-Id: Ic6d5f3e9d1415fcd9425b1afc767574a65556578
parent e1a70f91

cmds/uinput/README.md

+112 −90
Original line number Diff line number Diff line 
# Usage

##  Two options to use the uinput command:

### 1. Interactive through stdin:

type `uinput -` into the terminal, then type/paste commands to send to the binary.

Use Ctrl+D to signal end of stream to the binary (EOF).



This mode can be also used from an app to send uinput events.

For an example, see the cts test case at: [InputTestCase.java][2]

There are two ways to use the `uinput` command:



When using another program to control uinput in interactive mode, registering a

new input device (for example, a bluetooth joystick) should be the first step.

After the device is added, you need to wait for the _onInputDeviceAdded_

(see [InputDeviceListener][1]) notification before issuing commands

to the device.

Failure to do so will cause missed events and inconsistent behavior.

* **Recommended:** `uinput -` reads commands from standard input until End-of-File (Ctrl+D) is sent.

  This mode can be used interactively from a terminal or used to control uinput from another program

  or app (such as the CTS tests via [`UinputDevice`][UinputDevice]).

* `uinput <filename>` reads commands from a file instead of standard input.



### 2. Using a file as an input:

type `uinput <filename>`, and the file will be used an an input to the binary.

You must add a sufficient delay after a "register" command to ensure device

is ready. The interactive mode is the recommended method of communicating

with the uinput binary.

[UinputDevice]: https://cs.android.com/android/platform/superproject/main/+/main:cts/libs/input/src/com/android/cts/input/UinputDevice.java



All of the input commands should be in pseudo-JSON format as documented below.

See examples [here][3].

## Command format



The file can have multiple commands one after the other (which is not strictly

legal JSON format, as this would imply multiple root elements).

Input commands should be in JSON format, though the parser is in [lenient mode] to allow comments,

and integers can be specified in hexadecimal (e.g. `0xABCD`). The input file (or standard input) can

contain multiple commands, which will be executed in sequence. Simply add multiple JSON objects to

the file, one after the other without separators:



## Command description

```json5

{

  "id": 1,

  "command": "register",

  // ...

}

{

  "id": 1,

  "command": "delay",

  // ...

}

```



Many examples of command files can be found [in the CTS tests][cts-example-jsons].



[lenient mode]: https://developer.android.com/reference/android/util/JsonReader#setLenient(boolean)

[cts-example-jsons]: https://cs.android.com/android/platform/superproject/main/+/main:cts/tests/tests/hardware/res/raw/



## Command reference



### `register`



1. `register`

Register a new uinput device



| Field            | Type           | Description                |

|:-------------:|:-------------:|:-------------------------- |

| id            | integer       | Device id                  |

| command       | string        | Must be set to "register"  |

| name          | string        | Device name                |

| vid           | 16-bit integer| Vendor id                  |

| pid           | 16-bit integer| Product id                 |

| bus           | string        | Bus that device should use |

| configuration | int array     | uinput device configuration|

| ff_effects_max| integer       | ff_effects_max value       |

| abs_info      | array         | ABS axes information       |



Device ID is used for matching the subsequent commands to a specific device

to avoid ambiguity when multiple devices are registered.



Device bus is used to determine how the uinput device is connected to the host.

The options are "usb" and "bluetooth".



Device configuration is used to configure uinput device.  "type" field provides the UI_SET_*

control code, and data is a vector of control values to be sent to uinput device, depends on

the control code.

|:----------------:|:--------------:|:-------------------------- |

| `id`             | integer        | Device ID                  |

| `command`        | string         | Must be set to "register"  |

| `name`           | string         | Device name                |

| `vid`            | 16-bit integer | Vendor ID                  |

| `pid`            | 16-bit integer | Product ID                 |

| `bus`            | string         | Bus that device should use |

| `configuration`  | object array   | uinput device configuration|

| `ff_effects_max` | integer        | `ff_effects_max` value     |

| `abs_info`       | array          | Absolute axes information  |



`id` is used for matching the subsequent commands to a specific device to avoid ambiguity when

multiple devices are registered.



`bus` is used to determine how the uinput device is connected to the host. The options are `"usb"`

and `"bluetooth"`.



Device configuration is used to configure the uinput device. The `type` field provides a `UI_SET_*`

control code, and data is a vector of control values to be sent to the uinput device, which depends

on the control code.



| Field         |     Type      | Description                |

|:-------------:|:-------------:|:-------------------------- |

| type          | integer       | UI_SET_ control type       |

| data          | int array     | control values             |

| `type`        | integer       | `UI_SET_` control type     |

| `data`        | integer array | control values             |



`ff_effects_max` must be provided if `UI_SET_FFBIT` is used in `configuration`.



Device ff_effects_max must be provided if FFBIT is set.

`abs_info` fields are provided to set the device axes information. It is an array of below objects:



Device abs_info fields are provided to set the device axes information. It is an array of below

objects:

| Field         | Type          | Description                |

|:-------------:|:-------------:|:-------------------------- |

| code          | integer       | Axis code                  |

| info          | object        | ABS information object     |

| `code`        | integer       | Axis code                  |

| `info`        | object        | Axis information object    |



The axis information object is defined as below, with the fields having the same meaning as those

Linux's [`struct input_absinfo`][struct input_absinfo]:



ABS information object is defined as below:

| Field         | Type          | Description                |

|:-------------:|:-------------:|:-------------------------- |

| value         | integer       | Latest reported value      |

| minimum       | integer       | Minimum value for the axis |

| maximum       | integer       | Maximum value for the axis |

| fuzz          | integer       | fuzz value for noise filter|

| flat          | integer       | values to be discarded     |

| resolution    | integer       | resolution of axis         |



See [struct input_absinfo][4]) definitions.

| `value`       | integer       | Latest reported value      |

| `minimum`     | integer       | Minimum value for the axis |

| `maximum`     | integer       | Maximum value for the axis |

| `fuzz`        | integer       | fuzz value for noise filter|

| `flat`        | integer       | values to be discarded     |

| `resolution`  | integer       | resolution of axis         |



Example:

```json



```json5

{

  "id": 1,

  "command": "register",
@@ -104,19 +113,39 @@ Example: 
        }

  ]

}



```

2. `delay`



[struct input_absinfo]: https://cs.android.com/android/platform/superproject/main/+/main:bionic/libc/kernel/uapi/linux/input.h?q=%22struct%20input_absinfo%22



#### Waiting for registration



After the command is sent, there will be a delay before the device is set up by the Android input

stack, and `uinput` does not wait for that process to finish. Any commands sent to the device during

that time will be dropped. If you are controlling `uinput` by sending commands through standard

input from an app, you need to wait for [`onInputDeviceAdded`][onInputDeviceAdded] to be called on

an `InputDeviceListener` before issuing commands to the device. If you are passing a file to

`uinput`, add a `delay` after the `register` command to let registration complete.



[onInputDeviceAdded]: https://developer.android.com/reference/android/hardware/input/InputManager.InputDeviceListener.html



#### Unregistering the device



As soon as EOF is reached (either in interactive mode, or in file mode), the device that was created

will be unregistered. There is no explicit command for unregistering a device.



### `delay`



Add a delay to command processing



| Field         | Type          | Description                |

|:-------------:|:-------------:|:-------------------------- |

| id            | integer       | Device id                  |

| command       | string        | Must be set to "delay"     |

| duration      | integer       | Delay in milliseconds      |

| `id`          | integer       | Device ID                  |

| `command`     | string        | Must be set to "delay"     |

| `duration`    | integer       | Delay in milliseconds      |



Example:

```json



```json5

{

  "id": 1,

  "command": "delay",
@@ -124,20 +153,21 @@ Example: 
}

```



3. `inject`

Send an array of uinput event packets [type, code, value] to the uinput device

### `inject`



Send an array of uinput event packets to the uinput device



| Field         | Type          | Description                |

|:-------------:|:-------------:|:-------------------------- |

| id            | integer       | Device id                  |

| command       | string        | Must be set to "inject"    |

| events        | integer array | events to inject           |

| `id`          | integer       | Device ID                  |

| `command`     | string        | Must be set to "inject"    |

| `events`      | integer array | events to inject           |



The "events" parameter is an array of integers, encapsulates evdev input_event type, code and value,

see the example below.

The `events` parameter is an array of integers in sets of three: a type, an axis code, and an axis

value, like you'd find in Linux's `struct input_event`. For example, sending presses of the 0 and 1

keys would look like this:



Example:

```json

```json5

{

  "id": 1,

  "command": "inject",
@@ -153,14 +183,6 @@ Example: 
}

```



### Notes

1. As soon as EOF is reached (either in interactive mode, or in file mode),

the device that was created will be unregistered. There is no

explicit command for unregistering a device.

2. The `getevent` utility can used to print out the key events

for debugging purposes.



[1]: https://developer.android.com/reference/android/hardware/input/InputManager.InputDeviceListener.html

[2]: ../../../../cts/tests/tests/hardware/src/android/hardware/input/cts/tests/InputTestCase.java

[3]: ../../../../cts/tests/tests/hardware/res/raw/

[4]: ../../../../bionic/libc/kernel/uapi/linux/input.h
 
## Notes



The `getevent` utility can used to print out the key events for debugging purposes.