Why usd-hid cable no need driver?

一些USB设置，如明华的SRD-U100 USB版免安装驱动。何解？

请参考wikipedia

http://en.wikipedia.org/wiki/USB_human_interface_device_class

Other devices[edit]

The USB HID class specifications allow for myriad other devices under the USB HID class. Some examples are automobile simulation controllers, exercise machines, telephony devices, thermometers, audio controls and medical instrumentation. Even uninterruptible power supplies and software protection dongles^[6] declare themselves under this class, despite the fact they often have no human interface at all. Any device can be a USB HID class device as long as a designer meets the USB HID class logical specifications. This is not to say that there is no need to ship drivers for these devices, nor that an operating system will immediately recognize the device. This only means that the device can declare itself under the human interface device class.

任何设备只需要符合USB HID类逻辑规范就可以作为USB HID类设备使用。