Hardware Communication

This page covers the details of communication protocols Plover uses to capture keyboard or steno writer input.

Keyboard Capture & Output

Three implementations of keyboard capture and output are currently available:

• The Windows implementation installs low-level event hooks to listen for key presses, and the Win32 API’s SendInput to generate keystrokes.

• The macOS implementation uses Quartz’s Event Services API: event taps to listen for key presses, and keyboard events to generate keystrokes.

• For Linux and BSD, there are two implementations. If the display server is x11, an implementation based on Xlib’s xinput is used to listen for key presses, and xtest.fake_input to generate keystrokes. For all other display servers, for example wayland, an implementation based on evdev is used to listen for key presses, and uinput to generate keystrokes. The uinput implementation needs to know the keyboard layout of the system, which can be configured in the Plover Output configuration tap.

Before implementing new keyboard capture and output mechanisms for a new platform, make sure to set up the platform layer for your platform.

Capture

New keyboard capture methods can be implemented as a subclass of Capture; your implementation should translate platform-specific events into calls to key_down and key_up.

class MyKeyboardCapture(Capture):
  def start(self):
    self._thread = threading.Thread(target=self._run)
    self._thread.start()

  def _run(self):
    while True:
      key, pressed = ... # wait for key event

      if pressed:
        self.key_down(key)
      else:
        self.key_up(key)

Plover’s engine handles translating these calls into steno strokes, as well as handling keymaps and arpeggiation.

Output

New keyboard emulation methods can be implemented as a subclass of Output. It must implement all of the methods specified, by translating them to platform-specific input calls.

class MyKeyboardEmulation(Output):
  def send_backspaces(self, num):
    ...

  def send_string(self, s):
    ...

  def send_key_combination(self, combo):
    ...

Serial Protocols

Plover supports communicating with hobbyist, student, and professional steno writers through a serial interface. The most common protocols are Gemini PR for hobbyist writers and Stentura for Stenograph writers, but custom protocols may be implemented.

The SerialStenotypeBase class handles all of the connection establishment and configuration; when implementing a new serial interface, you only need to define your key layout and implement a way to parse each packet.

class MySerialMachine(SerialStenotypeBase):
  KEYS_LAYOUT = """
    ...
  """

  def run(self):
    ...

USB-based Protocols

Todo

Complete this section.

Other Protocols

Todo

Complete this section.