Update UART mode

- Update `_wakeup` to come out of power_down and put the pn532 back into
  normal mode.
- `_wait_ready` now actually checks to see if the pn532 is ready
- improve how data is written out

adafruit_pn532/uart.py

@@ -45,24 +45,34 @@ from adafruit_pn532.adafruit_pn532 import PN532, BusyError
 class PN532_UART(PN532):
     """Driver for the PN532 connected over Serial UART"""
 
-    def __init__(self, uart, *, irq=None, reset=None, debug=False):
+    def __init__(self, uart, *, reset=None, debug=False):
         """Create an instance of the PN532 class using Serial connection.
-        Optional IRQ pin (not used), reset pin and debugging output.
+        Optional reset pin and debugging output.
         """
         self.debug = debug
-        self._irq = irq
         self._uart = uart
         super().__init__(debug=debug, reset=reset)
 
     def _wakeup(self):
         """Send any special commands/data to wake up PN532"""
-        # self._write_frame([_HOSTTOPN532, _COMMAND_SAMCONFIGURATION, 0x01])
+        if self._reset_pin:
+            self._reset_pin.value = True
+            time.sleep(0.01)
+        self.low_power = False
+        self._uart.write(
+            b"\x55\x55\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
+        ) # wake up!
         self.SAM_configuration()
 
     def _wait_ready(self, timeout=1):
         """Wait `timeout` seconds"""
-        time.sleep(timeout)
-        return True
+        timestamp = time.monotonic()
+        while (time.monotonic() - timestamp) < timeout:
+            if self._uart.in_waiting > 0:
+                return True # No Longer Busy
+            time.sleep(0.01)  # lets ask again soon!
+        # Timed out!
+        return False
 
     def _read_data(self, count):
         """Read a specified count of bytes from the PN532."""
@@ -71,17 +81,9 @@ class PN532_UART(PN532):
             raise BusyError("No data read from PN532")
         if self.debug:
             print("Reading: ", [hex(i) for i in frame])
-        else:
-            time.sleep(0.1)
         return frame
 
     def _write_data(self, framebytes):
         """Write a specified count of bytes to the PN532"""
-        while self._uart.read(
-            1
-        ):  # this would be a lot nicer if we could query the # of bytes
-            pass
-        self._uart.write(
-            "\x55\x55\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
-        )  # wake up!
+        self._uart.reset_input_buffer()
         self._uart.write(framebytes)