rt21: Fix DTCS decoding when stored in hex

Apparently this radio has a bit for whether or not the DTCS code is
stored in hex or octal. CHIRP was only supporting octal format,
but radios with codes stored in hex were found in the wild and we,
of course, fail to decode those.

Fixes #11749

chirp/drivers/retevis_rt21.py

@@ -767,6 +767,8 @@ class RT21Radio(chirp_common.CloneModeRadio):
     _skipflags = True
     _reserved = False
     _mask = 0x2000  # bit mask to identify DTCS tone decoding is used
+    _dcs_octal = 0x0800  # bit mask to identify DTCS stored in octal
+    _dcs_inverse = 0x8000  # bit mask to identify inverted DTCS codes
     _gmrs = _frs = _pmr = False
     _echo = False
 
@@ -839,9 +841,29 @@ def get_raw_memory(self, number):
         return repr(self._memobj.memory[number - 1])
 
     def _get_tone(self, _mem, mem):
+        # 0xA662 = 662R = 1010 0...
+        # 0xA9DC = 734R = 1010 1...
+        # 0x29D3 = 723N - 0010 1...
+
         def _get_dcs(val):
-            code = int("%03o" % (val & 0x07FF))
-            pol = (val & 0x8000) and "R" or "N"
+            # 0x0800 means code is stored in hex instead of ocal (?!)
+            if val & self._dcs_octal:
+                code = int("%03o" % (val & 0x07FF))
+            else:
+                try:
+                    code = int("%03x" % (val & 0x07FF))
+                    if code not in chirp_common.DTCS_CODES:
+                        raise ValueError('DCS code assumed to be wrong')
+                except ValueError:
+                    # Memories may have been stored as octal but without the
+                    # proper bit flag in the past, so if we see something
+                    # recorded as "should be hex" but interpretation as hex
+                    # yields an invalid code, assume it's actually octal and
+                    # parse it as such.
+                    LOG.warning('Trying DCS conversion of 0x%04x as octal '
+                                'for compatibility', val)
+                    code = int("%03o" % (val & 0x07FF))
+            pol = (val & self._dcs_inverse) and "R" or "N"
             return code, pol
 
         tpol = False
@@ -1129,9 +1151,10 @@ def get_memory(self, number):
 
     def _set_tone(self, mem, _mem):
         def _set_dcs(code, pol):
-            val = int("%i" % code, 8) + self._mask
+            val = int("%i" % code, 8)
             if pol == "R":
-                val += 0x8000
+                val |= self._dcs_inverse
+            val |= self._mask | self._dcs_octal
             return val
 
         rx_mode = tx_mode = None
@@ -1919,7 +1942,6 @@ class RB26Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = True
 
     _ranges = [
@@ -1956,7 +1978,6 @@ class RT76Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = False
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = True
 
     _ranges = [
@@ -2038,7 +2059,6 @@ class RB23Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = True
 
     _ranges = [
@@ -2071,7 +2091,6 @@ class RT19Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = False
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _frs = True
 
     _ranges = [
@@ -2100,7 +2119,6 @@ class RT619Radio(RT19Radio):
                    0x100,   # memory start
                    _upper   # number of freqhops
                    )
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _frs = False
     _pmr = True
 
@@ -2128,7 +2146,6 @@ class AR63Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = False
 
     _ranges = [
@@ -2162,7 +2179,6 @@ class RT40BRadio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = True
     _echo = True
 
@@ -2194,7 +2210,6 @@ class RB28BRadio(RT21Radio):
     _ack_1st_block = False
     _skipflags = False
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _frs = True
 
     _ranges = [
@@ -2218,7 +2233,6 @@ class RB628BRadio(RB28BRadio):
     _magic = b"PHOGR\x09\xB2"
     _fingerprint = [b"P32073" + b"\x02\xFF", ]
     _upper = 16
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _frs = False
     _pmr = True
 
@@ -2243,7 +2257,6 @@ class RT86Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
 
     _ranges = [
                (0x0000, 0x01A0),