|USB : USB Classes A Closer Look at HID Class|
Feature Reports are special, in that they are the only type of HID data reports that can travel in EITHER direction, either TO or FROM the PC Host. (In the picture below, we only show the data being sent IN to the PC Host.)
Feature Reports were originally intended to be used to set properties or parameters of a HID device from something like a Control Panel applet, like for example the process of “calibrating” a joystick.
For this reason, Feature Reports are NOT requested or sent by the PC on a regular basis, but only rarely, when the end user does something.
This is another important concept: Unlike Input or Output data items, which can only be read by the PC or only be written by the PC, any Feature data item can either be written by the PC or read back by the PC. This means that any data item that you want to be able to set from the PC, and then be able to read back later, should be a Feature item.
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