diff --git a/killerbee/__init__.py b/killerbee/__init__.py
index ac4febf..63c3099 100644
--- a/killerbee/__init__.py
+++ b/killerbee/__init__.py
@@ -66,6 +66,13 @@ def __init__(self, device: Optional[str]=None, hardware: Optional[str]=None, dat
             gps_devstring = gps
 
         if hardware is not None and device is not None:
+            if ":" in device:
+                result = search_usb(None)
+                if result is not None:
+                    device = result
+                else:
+                    raise KBInterfaceError("Did not find a USB device matching %s." % device)
+
             if hardware == "apimote":
                 from .dev_apimote import APIMOTE
                 self.driver = APIMOTE(device)
diff --git a/killerbee/dev_cc253x.py b/killerbee/dev_cc253x.py
index edc9a12..4707d73 100644
--- a/killerbee/dev_cc253x.py
+++ b/killerbee/dev_cc253x.py
@@ -241,11 +241,12 @@ def pnext(self, timeout=100):
                 # in last two bytes of framedata. Note that we remove these before return of the frame.
 
                 # RSSI is signed value, offset by 73 (see CC2530 data sheet for offset)
-                rssi = framedata[-2] - 73
+                rssi = struct.unpack('b', framedata[-2:-1])[0] - 73
                 # Dirty hack to compensate for possible RSSI overflow
-                if rssi > 255:
-                    rssi = 255 # assumed to be max, could also report error/0
-
+                if rssi > 127 or rssi < -127:
+                    print(f"Rssi = {rssi}, out of range, setting to invalid valuei (-128)")
+                    rssi = -128 # invalid value according to PPI spec 
+         
                 fcsx = framedata[-1]
                 # validcrc is the bit 7 in fcsx
                 validcrc  = (fcsx & 0x80) == 0x80