#Usb operation drivers#
#Usb operation driver#

The first byte specifies the length of the descriptor, while the second byte indicates the descriptor type. Endpoint zero, the default control endpoint is always assumed to be a controlД®ndpoint and as such never has a descriptor.ДЄll descriptors are made up of a common format. Zero while we change the endpoint settings associated with interface one without effecting interface zero.Д®ach endpoint descriptor is used to specify the type of transfer, direction, polling interval and maximum This gives an advantage over having two configurations, in that we can be transmitting data over interface Of Interface one with a alternative setting of one to enable the other interface descriptor. However during operation the host can send a SetInterface request directed to that

When this configuration is enabled, the first two interface descriptors with bAlternativeSettingsД®qual to zero is used. Setting the bAlternativeSetting to one, indicating this interface descriptor can be anДЄlternative setting to that of the other interface descriptor two. We could then throw in another descriptor,ДЄlso with a bInterfaceNumber set to one indicating it is the second interface, but this time Interface two would have a bInterfaceNumber set to one indicating it is the second interfaceДЄnd a bAlternativeSetting of zero (default). Zero indicating it is the first interface descriptor and a bAlternativeSetting of zero. Interface one has bInterfaceNumber set to With two interfaces, interface one and interface two. Interface descriptors have a bInterfaceNumber field specifying the Interface number and aД«AlternateSetting which allows an interface to change settings on the fly. A device could haveДЎ or many interface descriptors enabled at once. Unlike the configurationДescriptor, there is no limitation as to having only one interface enabled at a time. Two the scanner function and Interface descriptor three the printer function. Interface descriptor one could describe the endpoints of the fax function, Interface descriptor For example you could have a multi-function fax/scanner/printerДevice. Performing a single feature of the device. The interface descriptor could be seen as a header or grouping of the endpoints into a functional group This flexibility, very few devices have more than 1 configuration. However it shouldД«e noted that changing the configuration requires all activity on each endpoint to stop. Same way and draw the same current, yet have different interface or endpoint combinations. Each configuration could be powered in the The configuration settings are not limited to power differences. Requiring the user to plug your device into the power point. If it is connected to a laptop or personal organiser it could enable the 2nd configuration (self powered) High power bus powered configuration enabling the device to be powered without a connection to the mains, yet

#Usb operation driver#

If the device is plugged into a host with a mains power supply, the device driver may choose to enable the It can only enable oneДЇor example, It is possible to have a high power bus powered configuration and a self powered configuration. Reads the device descriptors and can make a decision of which configuration to enable. If the device is self or bus powered and the number of interfaces it has. The configuration descriptor specifies values such as the amount of power this particular configuration uses, The number of configurations indicate how many configuration Of possible configurations the device can have.

#Usb operation drivers#

Revision the device complies to, the Product and Vendor IDs used to load the appropriate drivers and the number The device descriptor includes information such as what USB USB devices can only have one device descriptor. Who makes it, what version of USB it supports, how many ways it can be configured, the number of endpoints and All USB devices have a hierarchy of descriptors which describe to the host information such as what the device is,