# Peripheral Driver Development ## When to Use [DriverExtensionAbility](../../reference/apis-driverdevelopment-kit/js-apis-app-ability-driverExtensionAbility.md) is an **ExtensionAbility** of the driver type that provides the driver-related extension framework. If the capabilities of a device can be expanded by inserting an external hardware module, you can install the driver of the hardware module through an application. **DriverExtensionAbility** can be used to develop such applications. You can bind a [DriverExtensionAbility](../../reference/apis-driverdevelopment-kit/js-apis-app-ability-driverExtensionAbility.md) object to an application through **DriverExtensionManager** so that related transactions can be processed in the background based on the application request information. Each type of **ExtensionAbility** has its own context. The **DriverExtensionAbility** provides related capabilities through the [DriverExtensionContext](../../reference/apis-driverdevelopment-kit/js-apis-inner-application-driverExtensionContext.md). ## Environment Setup Set up the environment following the instructions in [Peripheral Driver Client Development](externaldevice-guidelines.md). The following table lists the SDK version requirements. | NDK API| SDK Version| |---------|--------| | USB DDK | API version 10 or later| | HID DDK | API version 11 or later| ## How to Develop To implement a driver, create a DriverExtensionAbility in the DevEco Studio project. The procedure is as follows: 1. In the **ets** directory of a module in the project, right-click and choose **New > Directory** to create a directory named **driverextability**. 2. In the **driverextability** directory, right-click and choose **New > ArkTS File** to create a file named **DriverExtAbility.ets**. 3. Import the related kit, and define the request code. ```ts import { DriverExtensionAbility } from '@kit.DriverDevelopmentKit'; import { Want } from '@kit.AbilityKit'; import { rpc } from '@kit.IPCKit'; const REQUEST_CODE = 99; // Negotaite the request code with the peripheral client. ``` 4. Open the **DriverExtAbility.ets** file, import the [RPC module](../../reference/apis-ipc-kit/js-apis-rpc.md), and overload the **onRemoteMessageRequest()** method to receive messages from the application and return the processing result to the application. **REQUEST_VALUE** is used to verify the service request code sent by the application. ```ts class StubTest extends rpc.RemoteObject { // Receive a message from the application and return the processing result to the client. onRemoteMessageRequest(code: number, data: rpc.MessageSequence, reply: rpc.MessageSequence, option: rpc.MessageOption) { if (code === REQUEST_CODE) { // Receive the data sent from the application. // When the application calls data.writeString() multiple times to write data, the driver can receive the corresponding data by calling data.readString() for multiple times. let optFir: string = data.readString(); // The driver returns the data processing result to the application. // In the example, Hello is received and Hello World is returned to the application. reply.writeString(optFir + ` World`); } return true; } } ``` 5. In the **DriverExtAbility.ets** file, import the dependency package [DriverExtensionAbility](../../reference/apis-driverdevelopment-kit/js-apis-app-ability-driverExtensionAbility.md), which provides the **onInit()**, **onRelease()**, **onConnect()**, and **onDisconnect()** lifecycle callbacks. Then, customize a class to inherit from [DriverExtensionAbility](../../reference/apis-driverdevelopment-kit/js-apis-app-ability-driverExtensionAbility.md) and override the lifecycle callbacks as required. ```ts export default class DriverExtAbility extends DriverExtensionAbility { onInit(want: Want) { console.info('testTag', `onInit, want: ${want.abilityName}`); } onRelease() { console.info('testTag', `onRelease`); } onConnect(want: Want) { console.info('testTag', `onConnect, want: ${want.abilityName}`); return new StubTest("test"); } onDisconnect(want: Want) { console.info('testTag', `onDisconnect, want: ${want.abilityName}`); } onDump(params: Array) { console.info('testTag', `onDump, params:` + JSON.stringify(params)); return ['params']; } } ``` 6. Register **DriverExtensionAbility** in the [**module.json5** file](../../quick-start/module-configuration-file.md) of the module in the project. Set **type** to **service** and **srcEntry** to the code path of **DriverExtensionAbility**. ```json { "module": { "name": "entry", "type": "entry", "description": "$string:module_desc", "mainElement": "EntryAbility", "deviceTypes": [ "default", "tablet" ], "requestPermissions": [ { "name": "ohos.permission.ACCESS_EXTENSIONAL_DEVICE_DRIVER" // Peripheral-specific permission, which is mandatory. } ], "deliveryWithInstall": true, "installationFree": false, "pages": "$profile:main_pages", "abilities": [ { "name": "EntryAbility", "srcEntry": "./ets/entryability/EntryAbility.ets", "description": "$string:EntryAbility_desc", "icon": "$media:startIcon", "label": "$string:EntryAbility_label", "startWindowIcon": "$media:startIcon", "startWindowBackground": "$color:start_window_background", "exported": true, "skills": [ { "entities": [ "entity.system.home" ], "actions": [ "action.system.home" ] } ] } ], "extensionAbilities": [ { "name": "DriverExtAbility", "icon": "$media:startIcon", "description": "driver", "type": "driver", "exported": true, "srcEntry": "./ets/driverextability/DriverExtAbility.ets", "metadata": [ { "name": "bus", // The bus is mandatory. "value": "USB" }, { "name": "desc", // Driver description, which is optional. "value": "the sample of driverExtensionAbility" }, { "name": "vendor", // Driver vendor name, which is optional. "value": "string" }, { "name": "vid," // List of USB vendor IDs. Enter a hex value. Here, the value is the hex value of 4817. "value": "0x12D1" }, { "name": "pid," // List of USB product IDs. Enter a hex value. Here, the value is the hex value of 4258. "value": "0x10A2" } ] } ] } } ``` 7. After completing development of the client and driver sample code, import the HAP to the device by following instructions in [Running Your App/Service on a Local Real Device](https://developer.huawei.com/consumer/en/doc/harmonyos-guides-V5/ide-run-device-V5), and run **Hello** in the HAP to check whether **Hello world** is displayed. If yes, the IPC communication is ready for use. ## Driver Development **DriverExtensionAbility** provides two development modes, namely, HID DDK and USB DDK, for driver development. Choose either mode depending on your need: * [HID DDK Development](https://gitee.com/openharmony/docs/blob/master/en/application-dev/napi/hid-ddk-guidelines.md) * [USB DDK Development](https://gitee.com/openharmony/docs/blob/master/en/application-dev/napi/usb-ddk-guidelines.md) ## Application Signing You need to configure a signature file for your application to run on a device. Besides, to develop a peripheral driver client, you need to declare the **ohos.permission.ACCESS_EXTENSIONAL_DEVICE_DRIVER** permission for the peripheral. If the HID DDK or USB DDK is used, configure the required permission as described above. Automatic signing: [Signing Your App/Service Automatically](https://developer.huawei.com/consumer/en/doc/harmonyos-guides-V5/ide-signing-V5#section18815157237) Permission configuration: [Requesting ACL Permissions and Signing Your App/Service](https://developer.huawei.com/consumer/en/doc/harmonyos-guides-V5/ide-signing-V5#section157591551175916).