[geocom] added CRC checksum support

Author: MrClock8163

src/geocompy/geo/__init__.py

@@ -46,7 +46,11 @@
 from serial import SerialException, SerialTimeoutException
 
 from geocompy.data import Angle, Byte
-from geocompy.communication import Connection, DUMMYLOGGER
+from geocompy.communication import (
+    Connection,
+    DUMMYLOGGER,
+    crc16_bytewise as crc16
+)
 from .gctypes import (
     GeoComCode,
     GeoComResponse,
@@ -120,16 +124,18 @@ class GeoCom(GeoComType):
     _R1P: re.Pattern[str] = re.compile(
         r"^%R1P,"
         r"(\d+),"  # COM code
-        r"(\d+):"  # Transaction ID
-        r"(\d+)"  # RPC code
+        r"(\d+)"  # Transaction ID
+        r"(?:,(\d+))?"  # CRC checksum
+        r":(\d+)"  # RPC code
         r"(?:,(.*))?$"  # parameters
     )
 
     def __init__(
         self,
         connection: Connection,
         logger: Logger | None = None,
-        retry: int = 2
+        retry: int = 2,
+        crc: bool = False
     ):
         """
         After the subsystems are initialized, the connection is tested by
@@ -229,6 +235,8 @@ def __init__(
         .. versionremoved:: GeoCOM-TPS1200
         """
 
+        self._crc: bool = crc
+
         for i in range(retry):
             try:
                 self._conn.send("\n")
@@ -355,6 +363,11 @@ def request(
         trid = self.transaction_counter % _MAX_TRANSACTION
         self.transaction_counter += 1
         cmd = f"%R1Q,{rpc},{trid}:{','.join(strparams)}"
+
+        if self._crc:
+            crc = crc16(cmd)
+            cmd = f"%R1Q,{rpc},{trid},{crc}:{','.join(strparams)}"
+
         try:
             answer = self._conn.exchange(cmd)
         except SerialTimeoutException:
@@ -432,7 +445,7 @@ def parse_response(
 
         """
         m = self._R1P.match(response)
-        _, rpc, trid_expected = cmd.split(":")[0].split(",")
+        rpc, trid_expected = cmd.split(":")[0].split(",")[1:3]
         rpcname = rpcnames.get(int(rpc), rpc)
         if not m:
             return GeoComResponse(
@@ -444,7 +457,20 @@ def parse_response(
                 0
             )
 
-        com_field, tr_field, rpc_field, values = m.groups()
+        com_field, tr_field, crc_field, rpc_field, values = m.groups()
+        if crc_field is not None:
+            crc = int(crc_field)
+            beg, end = m.regs[3]
+            if crc != crc16(response[:beg-1] + response[end:]):
+                return GeoComResponse(
+                    rpcname,
+                    cmd,
+                    response,
+                    GeoComCode.COM_CLNT_RX_CHECKSUM_ERROR,
+                    GeoComCode.OK,
+                    0
+                )
+
         trid = int(tr_field)
         if trid != int(trid_expected):
             return GeoComResponse(
@@ -467,9 +493,6 @@ def parse_response(
             rpccode = GeoComCode.UNDEFINED
 
         if values is None:
-            values = ""
-
-        if values == "":
             return GeoComResponse(
                 rpcname,
                 cmd,