How to select a USB interface setting (UWP app)
This article demonstrates how to change a setting within a USB interface. Use the UsbInterfaceSetting object to get the current setting and set a setting in the interface.
Before you start
- You must have opened the device and obtained the UsbDevice object. Read How to connect to a USB device (UWP app).
- Code examples are based on the CustomUSBDevice sample. You can download the complete sample from this code gallery page.
About USB interface settings
Each USB interface exposes one or more endpoints that are grouped in interface settings. Those settings are device-defined and identified with a number called the setting index. Each interface must have only one active setting. For a multiple interface device, each interface must have an active setting. If a setting is active, data can be transferred to or from its endpoints. Endpoints in non-active settings are disabled for data transfers.
A setting is said to be active after it has been selected on the device. The default active setting is the first setting of an interface.
Each setting is represented by a UsbInterfaceSetting object. By using the object, your UWP app can perform these operations:
- Determine whether a particular setting is active while enumerating all settings in an interface.
- Initiate a request that selects an setting.
For information about USB interface settings, see USB device layout.
Get the active setting of a USB interface
- Get the UsbInterface object from the previous obtained UsbDevice object. This code example gets the first interface in the USB configuration. For a multiple-interface device, you can get the UsbInterface object that you want to use by enumerating all interfaces. You can get that array through the UsbConfiguration.UsbInterfaces property value.
- Get all settings defined in the interface as an array of UsbInterfaceSetting objects by getting the UsbInterface.InterfaceSettings property value.
- Enumerate the array and in each iteration check whether the setting is active by checking the UsbInterfaceSetting.Selected property.
This example code shows how to get the setting number for all settings defined in the default interface.
void GetInterfaceSetting (UsbDevice device)
{
auto interfaceSettings = device.InterfaceSettings;
for each(UsbInterfaceSetting interfaceSetting in interfaceSettings)
{
if (interfaceSetting->Selected)
{
uint8 interfaceSettingNumber = interfaceSetting.InterfaceDescriptor.AlternateSettingNumber;
// Use the interface setting number. Not shown.
break;
}
}
}
Set a USB interface setting
To select a setting that is not currently active, you must find the UsbInterfaceSetting object for the setting to select and then start an asynchronous operation by calling the UsbInterfaceSetting.SelectSettingAsync method. The operation does not return a value.
private async void SetInterfaceSetting(UsbDevice device, Byte settingNumber)
{
var interfaceSetting = device.DefaultInterface.InterfaceSettings[settingNumber];
await interfaceSetting.SelectSettingAsync();
MainPage.Current.NotifyUser("Interface Setting is set to " + settingNumber, NotifyType.StatusMessage);
}