From c8a97e273acd58e2e46811002200291fcc82615d Mon Sep 17 00:00:00 2001
From: Bryan Biedenkapp <gatekeep@gmail.com>
Date: Fri, 2 Jan 2026 10:29:10 -0500
Subject: [PATCH] add support for DVM's internal LC_CALL_TERM TSBK;

---
 FneSystemBase.cs                    | 27 +++++++++-
 P25/P25Defines.cs                   |  1 +
 P25/lc/tsbk/OSP_DVM_LC_CALL_TERM.cs | 80 +++++++++++++++++++++++++++++
 3 files changed, 107 insertions(+), 1 deletion(-)
 create mode 100644 P25/lc/tsbk/OSP_DVM_LC_CALL_TERM.cs

diff --git a/FneSystemBase.cs b/FneSystemBase.cs
index 2699275..03f6f28 100644
--- a/FneSystemBase.cs
+++ b/FneSystemBase.cs
@@ -7,7 +7,7 @@
 * @package DVM / Fixed Network Equipment Core Library
 * @license AGPLv3 License (https://opensource.org/licenses/AGPL-3.0)
 *
-*   Copyright (C) 2024-2025 Bryan Biedenkapp, N2PLL
+*   Copyright (C) 2024-2026 Bryan Biedenkapp, N2PLL
 *
 */
 
@@ -22,6 +22,7 @@ using fnecore.EDAC;
 using fnecore.DMR;
 using fnecore.P25;
 using fnecore.NXDN;
+using fnecore.P25.LC.TSBK;
 
 namespace fnecore
 {
@@ -526,6 +527,30 @@ namespace fnecore
             peer.SendMaster(FneBase.CreateOpcode(Constants.NET_FUNC_PROTOCOL, Constants.NET_PROTOCOL_SUBFUNC_P25), payload, Constants.RtpCallEndSeq, callData.TxStreamID);
         }
 
+        /// <summary>
+        /// Helper to send a DVM call termination TSDU.
+        /// </summary>
+        /// <param name="srcId"></param>
+        /// <param name="dstId"></param>
+        public void SendDVMCallTermination(uint srcId, uint dstId)
+        {
+            OSP_DVM_LC_CALL_TERM osp = new OSP_DVM_LC_CALL_TERM(dstId, srcId);
+
+            RemoteCallData callData = new RemoteCallData
+            {
+                MFId = P25Defines.P25_MFG_DVM_OCS,
+                SrcId = srcId,
+                DstId = dstId,
+                LCO = P25Defines.LC_CALL_TERM
+            };
+
+            byte[] tsbk = new byte[P25Defines.P25_TSBK_LENGTH_BYTES];
+
+            osp.Encode(ref tsbk);
+
+            SendP25TSBK(callData, tsbk);
+        }
+
         /// <summary>
         /// Helper to send a P25 TDU message.
         /// </summary>
diff --git a/P25/P25Defines.cs b/P25/P25Defines.cs
index 345fb85..0328497 100644
--- a/P25/P25Defines.cs
+++ b/P25/P25Defines.cs
@@ -154,6 +154,7 @@ namespace fnecore.P25
         public const byte P25_FT_DATA_UNIT = 0x00;
 
         public const byte P25_MFG_STANDARD = 0x00;
+        public const byte P25_MFG_DVM_OCS = 0x9C;
 
         public const byte P25_ALGO_UNENCRYPT = 0x80;
         public const byte P25_ALGO_DES = 0x81;
diff --git a/P25/lc/tsbk/OSP_DVM_LC_CALL_TERM.cs b/P25/lc/tsbk/OSP_DVM_LC_CALL_TERM.cs
new file mode 100644
index 0000000..543a4f1
--- /dev/null
+++ b/P25/lc/tsbk/OSP_DVM_LC_CALL_TERM.cs
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+/**
+* Digital Voice Modem - Fixed Network Equipment Core Library
+* AGPLv3 Open Source. Use is subject to license terms.
+* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+*
+* @package DVM / Fixed Network Equipment Core Library
+* @license AGPLv3 License (https://opensource.org/licenses/AGPL-3.0)
+*
+*   Copyright (C) 2026 Bryan Biedenkapp, N2PLL
+*
+*/
+
+namespace fnecore.P25.LC.TSBK
+{
+    /// <summary>
+    /// OSP_DVM_LC_CALL_TERM TSBK
+    /// </summary>
+    public class OSP_DVM_LC_CALL_TERM : TSBKBase
+    {
+        public byte GrpVchId;
+        public uint GrpVchNo;
+        public uint DstId;
+        public uint SrcId;
+
+        /// <summary>
+        /// Creates an instance of <see cref="OSP_DVM_LC_CALL_TERM"/>
+        /// </summary>
+        /// <param name="dstId"></param>
+        /// <param name="srcId"></param>
+        public OSP_DVM_LC_CALL_TERM(uint dstId = 0, uint srcId = 0)
+        {
+            DstId = dstId;
+            SrcId = srcId;
+            Lco = P25Defines.LC_CALL_TERM;
+        }
+
+        /// <summary>
+        /// Decode CALL_ALRT TSBK
+        /// </summary>
+        /// <param name="data"></param>
+        /// <param name="rawTSBK"></param>
+        /// <returns></returns>
+        public override bool Decode(byte[] data, bool rawTSBK = true)
+        {
+            if (!base.Decode(data, rawTSBK))
+                return false;
+
+            ulong tsbkValue = FneUtils.ToUInt64(Payload, 0);
+
+            GrpVchId = (byte)((tsbkValue >> 52) & 0x0F);    // Channel ID
+            GrpVchNo = (uint)((tsbkValue >> 40) & 0xFFF);   // Channel Number
+            DstId = (uint)((tsbkValue >> 24) & 0xFFFF);     // Target Radio Address
+            SrcId = (uint)(tsbkValue & 0xFFFFFF);           // Source Radio Address
+
+            return true;
+        }
+
+        /// <summary>
+        /// Encode CALL_ALRT TSBK
+        /// </summary>
+        /// <param name="data"></param>
+        /// <param name="payload"></param>
+        /// <param name="rawTSBK"></param>
+        /// <param name="noTrellis"></param>
+        public override void Encode(ref byte[] data, bool rawTSBK = true, bool noTrellis = true)
+        {
+            ulong tsbkValue = 0;
+            tsbkValue = (tsbkValue << 4) + GrpVchNo;        // Channel ID
+            tsbkValue = (tsbkValue << 12) + GrpVchId;       // Channel Number
+            tsbkValue = (tsbkValue << 16) + DstId;          // Target Radio Address
+            tsbkValue = (tsbkValue << 24) + SrcId;          // Source Radio Address
+
+            FneUtils.Memset(Payload, 0x00, Payload.Length);
+            FneUtils.WriteBytes(tsbkValue, ref Payload, 0);
+
+            base.Encode(ref data, rawTSBK, noTrellis);
+        }
+    } // public class OSP_DVM_LC_CALL_TERM
+} // namespace fnecore.P25.LC.TSBK