When using another program to control hid in interactive mode, registering a new input device (for example, a bluetooth joystick) should be the first step. After the device is added, you need to wait for the onInputDeviceAdded (see InputDeviceListener) notification before issuing commands to the device. Failure to do so will cause missed events and inconsistent behaviour. In the current implementation of the hid command, the hid binary will wait for the file descriptor to the uhid node to send the UHID_START and UHID_OPEN signals before returning. However, this is not sufficient. These signals only notify the readiness of the kernel driver, but do not take into account the inputflinger framework.

2. Using a file as an input:

type hid <filename>, and the file will be used an an input to the binary. You must add a sufficient delay after a "register" command to ensure device is ready. The interactive mode is the recommended method of communicating with the hid binary.

All of the input commands should be in pseudo-JSON format as documented below. See examples here.

The file can have multiple commands one after the other (which is not strictly legal JSON format, as this would imply multiple root elements).

Command description

register Register a new uhid device

Field	Type	Description
id	integer	Device id
command	string	Must be set to "register"
name	string	Device name
vid	16-bit integer	Vendor id
pid	16-bit integer	Product id
bus	string	Bus that device should use
descriptor	byte array	USB HID report descriptor

Device ID is used for matching the subsequent commands to a specific device to avoid ambiguity when multiple devices are registered.

Device bus is used to determine how the uhid device is connected to the host. The options are "usb" and "bluetooth".

USB HID report descriptor should be generated according the the USB HID spec and can be checked by reverse parsing using a variety of tools, for example usbdescreqparser.

Example:

{
  "id": 1,
  "command": "register",
  "name": "Odie (Test)",
  "vid": 0x18d1,
  "pid": 0x2c40,
  "bus": "usb",
  "descriptor": [0x05, 0x01, 0x09, 0x05, 0xa1, 0x01, 0x85, 0x01, 0x05, 0x09, 0x0a, 0x01, 0x00,
    0x0a, 0x02, 0x00, 0x0a, 0x04, 0x00, 0x0a, 0x05, 0x00, 0x0a, 0x07, 0x00, 0x0a, 0x08, 0x00,
    0x0a, 0x0e, 0x00, 0x0a, 0x0f, 0x00, 0x0a, 0x0d, 0x00, 0x05, 0x0c, 0x0a, 0x24, 0x02, 0x0a,
    0x23, 0x02, 0x15, 0x00, 0x25, 0x01, 0x75, 0x01, 0x95, 0x0b, 0x81, 0x02, 0x75, 0x01, 0x95,
    0x01, 0x81, 0x03, 0x05, 0x01, 0x75, 0x04, 0x95, 0x01, 0x25, 0x07, 0x46, 0x3b, 0x01, 0x66,
    0x14, 0x00, 0x09, 0x39, 0x81, 0x42, 0x66, 0x00, 0x00, 0x09, 0x01, 0xa1, 0x00, 0x09, 0x30,
    0x09, 0x31, 0x09, 0x32, 0x09, 0x35, 0x05, 0x02, 0x09, 0xc5, 0x09, 0xc4, 0x15, 0x00, 0x26,
    0xff, 0x00, 0x35, 0x00, 0x46, 0xff, 0x00, 0x75, 0x08, 0x95, 0x06, 0x81, 0x02, 0xc0, 0x85,
    0x02, 0x05, 0x08, 0x0a, 0x01, 0x00, 0x0a, 0x02, 0x00, 0x0a, 0x03, 0x00, 0x0a, 0x04, 0x00,
    0x15, 0x00, 0x25, 0x01, 0x75, 0x01, 0x95, 0x04, 0x91, 0x02, 0x75, 0x04, 0x95, 0x01, 0x91,
    0x03, 0xc0, 0x05, 0x0c, 0x09, 0x01, 0xa1, 0x01, 0x85, 0x03, 0x05, 0x01, 0x09, 0x06, 0xa1,
    0x02, 0x05, 0x06, 0x09, 0x20, 0x15, 0x00, 0x26, 0xff, 0x00, 0x75, 0x08, 0x95, 0x01, 0x81,
    0x02, 0x06, 0xbc, 0xff, 0x0a, 0xad, 0xbd, 0x75, 0x08, 0x95, 0x06, 0x81, 0x02, 0xc0, 0xc0]
}

delay Add a delay to command processing

Field	Type	Description
id	integer	Device id
command	string	Must be set to "delay"
duration	integer	Delay in milliseconds

Example:

{
  "id": 1,
  "command": "delay",
  "duration": 10
}

report Send a report to the HID device

Field	Type	Description
id	integer	Device id
command	string	Must be set to "report"
report	byte array	Report data to send

Example:

{
  "id": 1,
  "command": "report",
  "report": [0x01, 0x01, 0x80, 0x7f, 0x7f, 0x7f, 0x7f, 0x00, 0x00]
}

Sending a joystick button press event

To send a button press event on a joystick device:

Register the joystick device
Send button down event with coordinates ABS_X, ABS_Y, ABS_Z, and ABS_RZ at the center of the range. If the coordinates are not centered, this event will generate a motion event within the input framework, in addition to the button press event. The range can be determined from the uhid report descriptor.
Send the button up event with the same coordinates as in 2.
Check that the button press event was received.

Notes

As soon as EOF is reached (either in interactive mode, or in file mode), the device that was created will be unregistered. There is no explicit command for unregistering a device.
The linux input subsystem does not generate events for those values that remain unchanged. For example, if there are two events sent to the driver, and both events have the same value of ABS_X, then ABS_X coordinate will not be reported.
The description of joystick actions is available here.
Joysticks are split axes. When an analog stick is in a resting state, the reported coordinates are at the center of the range.
The getevent utility can used to print out the key events for debugging purposes.