+            # check tx and rx have hardware support
+            for portId, portTx, portRx in uartPorts:  #
+                if portTx == tx and portRx == rx:
+                    self._uart = _UART(
+                        portId,
+                        baudrate,
+                        bits=bits,
+                        parity=parity,
+                        stop=stop,
+                        timeout=timeout,
+                        read_buf_len=receiver_buffer_size,
+                    )
+                    break
+            else:
+                raise ValueError(
+                    "No Hardware UART on (tx,rx)={}\nValid UART ports: {}".format(
+                        (tx, rx), uartPorts
+                    )