* Author(s): cefn
 """
+import os
 
 try:
     import threading
             self._i2c = _I2C(frequency=frequency)
             return
         if detector.board.microchip_mcp2221:
-            from adafruit_blinka.microcontroller.mcp2221.i2c import I2C as _I2C
-
+            if "BLINKA_FORCECHIP" in os.environ and os.environ["BLINKA_FORCEBOARD"] == "MICROCHIP_MCP2221":
+                from adafruit_blinka.microcontroller.fake_mcp2221.i2c import I2C as _I2C
+            else:
+                from adafruit_blinka.microcontroller.mcp2221.i2c import I2C as _I2C
             self._i2c = _I2C(frequency=frequency)
             return
         if detector.board.greatfet_one:
             if end is None:
                 end = len(buffer)
             buffer = memoryview(buffer)[start:end]
-        stop = True  # remove for efficiency later
-        return self._i2c.readfrom_into(address, buffer, stop=stop)
+        return self._i2c.readfrom_into(address, buffer, stop=True)
 
-    def writeto(self, address, buffer, *, start=0, end=None, stop=True):
+    def writeto(self, address, buffer, *, start=0, end=None):
         """Write to a device at specified address from a buffer"""
         if isinstance(buffer, str):
             buffer = bytes([ord(x) for x in buffer])
         if start != 0 or end is not None:
             if end is None:
-                return self._i2c.writeto(address, memoryview(buffer)[start:], stop=stop)
-            return self._i2c.writeto(address, memoryview(buffer)[start:end], stop=stop)
-        return self._i2c.writeto(address, buffer, stop=stop)
+                return self._i2c.writeto(address, memoryview(buffer)[start:], stop=True)
+            return self._i2c.writeto(address, memoryview(buffer)[start:end], stop=True)
+        return self._i2c.writeto(address, buffer, stop=True)
 
     def writeto_then_readfrom(
         self,