Add code for SNES mouse to USB HID with CircuitPython

Author: jepler

CircuitPython_SNES_Mouse/code.py

@@ -0,0 +1,66 @@
+import time
+import board
+import digitalio
+from adafruit_hid.mouse import Mouse
+from usb_hid import devices
+
+SCALE = 3
+
+def delta(value): # Convert 8 bit value to signed number of distance steps
+    value = ~value # All value is inverted on the bus
+    if value & 0x80:  # and is in sign-magnitude format
+        return -(value & 0x7f)
+    else:
+        return value & 0x7f
+
+mouse = Mouse(devices)
+
+spi = board.SPI()
+strobe = digitalio.DigitalInOut(board.RX)
+strobe.switch_to_output(False)
+
+if not spi.try_lock():
+    raise SystemExit("could not lock SPI bus")
+
+spi.configure(baudrate=100_000, polarity=1)
+
+# Wait for the mouse to be ready at power-on
+time.sleep(2)
+
+# A buffer to fetch mouse data into
+data = bytearray(4)
+
+print("Mouse is ready!")
+while True:
+    # Request fresh data
+    strobe.value = True
+    strobe.value = False
+
+    # Must do read in 2 pieces with delay in between
+    spi.readinto(data, end=2)
+    spi.readinto(data, start=2)
+    lmb = bool(~data[1] & 0x40)  # data is inverted on the bus
+    rmb = bool(~data[1] & 0x80)
+    dy = delta(data[2])
+    dx = delta(data[3])
+
+
+    # Pressing both buttons together emulates the wheel
+    wheel = lmb and rmb
+
+    # Compute the new button state
+    old_buttons = mouse.report[0]
+    mouse.report[0] = (
+        0 if wheel else
+        mouse.LEFT_BUTTON if lmb else
+        mouse.RIGHT_BUTTON if rmb else
+        0)
+
+    # If there's any movement, send a move event
+    if dx or dy:
+        if wheel:
+            mouse.move(dx * SCALE, 0, wheel=-dy)
+        else:
+            mouse.move(dx * SCALE, dy * SCALE)
+    elif old_buttons != mouse.report[0]:
+        mouse.press(0) # Send buttons previously set via report[0]