The USB HID (Human Interface Device) class modules provided in this SDK implement the HID class and subclasses that have been defined in the following specification:
Device Class Definition for Human Interface Devices (HID)
The specification defines three protocols:
- Mouse
- Keyboard
- Generic
The modules that implement these HID protocols are organized in the same way. All HID protocol implementations use the same parent module in which the common functionality is implemented. The following figure shows how data structures are inherited in HID modules:
HID reports
For more detailed information on the reports for the keyboard and mouse protocol implementations, refer to the Device Class Definition for Human Interface Devices (HID) document.
For all USB HID classes, you must define one IN endpoint for the input reports. Defining an OUT endpoint is optional and if it is not set, output reports are sent through the control endpoint. The following figure shows a typical HID report flow between a USB host and the device:
Mouse report
For the mouse protocol, one 4-byte input report is defined:
- BYTE[0]: Button state bit field.
- BYTE[1]: Signed 8-b it X-axis offset since the last position.
- BYTE[2]: Signed 8-bit Y-axis offset since the last position.
- BYTE[3]: signed 8-bit Wheel offset since the last position.
Keyboard reports
For the keyboard protocol, two reports are defined:
- IN keyboard state report:
- BYTE[0]: Keyboard modifier. For example, the Shift key state.
- BYTE[1]: Reserved.
- BYTE[2]: Key 0 state.
- BYTE[3]: Key 1 state.
- BYTE[4]: Key 2 state.
- BYTE[5]: Key 3 state.
- BYTE[6]: Key 4 state.
- BYTE[7]: Key 5 state.
OUT LED state report:
- BYTE[0]: LED state, such as CapsLock LED or NumLock LED.
Generic reports
The generic HID protocol implementation does not define any reports. Instead, it allows you to create and handle custom, user-defined report descriptors and reports. All information about the report flow is passed to the user event handler by the APP_USBD_HID_USER_EVT_IN_REPORT_DONE, APP_USBD_HID_USER_EVT_OUT_REPORT_READY and APP_USBD_HID_USER_EVT_FEATURE_REPORT_READY events.
For an example on how to use the USB HID mouse and keyboard classes, refer to the USB HID Composite Example.