add more P25 Phase 2 primitives for S-OEMI sync and Hamming (8,4,4) for P2 DUID handling;

src/common/edac/Hamming.cpp

@@ -5,6 +5,7 @@
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  *  Copyright (C) 2015,2016 Jonathan Naylor, G4KLX
+ *  Copyright (C) 2026 Bryan Biedenkapp, N2PLL
  *
  */
 #include "edac/Hamming.h"
@@ -360,3 +361,93 @@ void Hamming::encode17123(bool* d)
     d[15] = d[0] ^ d[1] ^ d[4] ^ d[5] ^ d[7] ^ d[10];
     d[16] = d[0] ^ d[1] ^ d[2] ^ d[5] ^ d[6] ^ d[8] ^ d[11];
 }
+
+/* Decode Hamming (8,4,4). */
+
+bool Hamming::decode844(bool* d)
+{
+    assert(d != nullptr);
+
+    // Hamming(8,4,4) extended code layout:
+    // d[0..3] = data bits (4 bits)
+    // d[4..6] = parity bits (3 bits) - Hamming(7,4,3) parity
+    // d[7]    = overall parity bit (1 bit)
+    //
+    // Parity check matrix:
+    // P0 (d[4]) = d[0] ^ d[1] ^ d[3]
+    // P1 (d[5]) = d[0] ^ d[2] ^ d[3]
+    // P2 (d[6]) = d[1] ^ d[2] ^ d[3]
+    // P3 (d[7]) = d[0] ^ d[1] ^ d[2] ^ d[3] ^ d[4] ^ d[5] ^ d[6] (overall parity)
+
+    // Calculate syndrome bits for Hamming(7,4,3) portion
+    bool c0 = d[0] ^ d[1] ^ d[3] ^ d[4];  // Check P0
+    bool c1 = d[0] ^ d[2] ^ d[3] ^ d[5];  // Check P1
+    bool c2 = d[1] ^ d[2] ^ d[3] ^ d[6];  // Check P2
+
+    // Calculate overall parity
+    bool c3 = d[0] ^ d[1] ^ d[2] ^ d[3] ^ d[4] ^ d[5] ^ d[6] ^ d[7];
+
+    // Build syndrome
+    unsigned char syndrome = 0x00U;
+    syndrome |= c0 ? 0x01U : 0x00U;
+    syndrome |= c1 ? 0x02U : 0x00U;
+    syndrome |= c2 ? 0x04U : 0x00U;
+
+    // If overall parity is wrong and syndrome is non-zero, single bit error
+    // If overall parity is wrong and syndrome is zero, error in parity bit d[7]
+    // If overall parity is correct and syndrome is non-zero, double bit error (uncorrectable)
+    // If both are correct, no error
+
+    if (c3) {
+        // Overall parity error detected
+        if (syndrome == 0x00U) {
+            // Error in overall parity bit
+            d[7] = !d[7];
+            return true;
+        }
+        else {
+            // Single bit error - syndrome tells us which bit
+            switch (syndrome) {
+                case 0x03U: d[0] = !d[0]; return true;  // d0 position
+                case 0x05U: d[1] = !d[1]; return true;  // d1 position
+                case 0x06U: d[2] = !d[2]; return true;  // d2 position
+                case 0x07U: d[3] = !d[3]; return true;  // d3 position
+                case 0x01U: d[4] = !d[4]; return true;  // P0 position
+                case 0x02U: d[5] = !d[5]; return true;  // P1 position
+                case 0x04U: d[6] = !d[6]; return true;  // P2 position
+                default: return false;  // Should not happen
+            }
+        }
+    }
+    else {
+        // Overall parity correct
+        if (syndrome == 0x00U) {
+            // No errors
+            return false;
+        }
+        else {
+            // Double bit error detected - uncorrectable
+            return false;
+        }
+    }
+}
+
+/* Encode Hamming (8,4,4). */
+
+void Hamming::encode844(bool* d)
+{
+    assert(d != nullptr);
+
+    // Hamming(8,4,4) extended code
+    // d[0..3] = data bits (input)
+    // d[4..6] = parity bits (calculated)
+    // d[7]    = overall parity bit (calculated)
+
+    // Calculate Hamming(7,4,3) parity bits
+    d[4] = d[0] ^ d[1] ^ d[3];              // P0
+    d[5] = d[0] ^ d[2] ^ d[3];              // P1
+    d[6] = d[1] ^ d[2] ^ d[3];              // P2
+
+    // Calculate overall parity bit
+    d[7] = d[0] ^ d[1] ^ d[2] ^ d[3] ^ d[4] ^ d[5] ^ d[6];
+}

src/common/edac/Hamming.h

@@ -5,6 +5,7 @@
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  *  Copyright (C) 2015,2016 Jonathan Naylor, G4KLX
+ *  Copyright (C) 2026 Bryan Biedenkapp, N2PLL
  *
  */
 /**
@@ -102,6 +103,18 @@ namespace edac
          * @param d Boolean bit array.
          */
         static void encode17123(bool* d);
+
+        /**
+         * @brief Decode Hamming (8,4,4).
+         * @param d Boolean bit array.
+         * @returns bool True, if bit errors are detected, otherwise false.
+         */
+        static bool decode844(bool* d);
+        /**
+         * @brief Encode Hamming (8,4,4).
+         * @param d Boolean bit array.
+         */
+        static void encode844(bool* d);
     };
 } // namespace edac
 

src/common/p25/P25Defines.h

@@ -66,6 +66,11 @@ namespace p25
         const uint32_t  P25_P2_FRAME_LENGTH_BYTES = 40U;
         const uint32_t  P25_P2_FRAME_LENGTH_BITS = P25_P2_FRAME_LENGTH_BYTES * 8U;
 
+        const uint32_t  P25_P2_IEMI_LENGTH_BITS = 312U;
+        const uint32_t  P25_P2_IEMI_LENGTH_BYTES = (P25_P2_IEMI_LENGTH_BITS / 8U) + 1U;
+        const uint32_t  P25_P2_SOEMI_LENGTH_BITS = 270U;
+        const uint32_t  P25_P2_SOEMI_LENGTH_BYTES = (P25_P2_SOEMI_LENGTH_BITS / 8U) + 1U;
+
         const uint32_t  P25_NID_LENGTH_BYTES = 8U;
         const uint32_t  P25_NID_LENGTH_BITS = P25_NID_LENGTH_BYTES * 8U;
 
@@ -852,6 +857,24 @@ namespace p25
             };
         }
 
+        // TIA-102.BBAD-D Section 4.2
+        /** @brief Phase 2 MAC 4V/SACCH Offset(s) */
+        namespace P2_MAC_HEADER_OFFSET {
+            /** @brief Phase 2 MAC 4V/SACCH Offset(s) */
+            enum : uint8_t {
+                FIRST_4V_NEXT = 0x00U,                  //!< First 4V Next non-SACCH Burst on Slot
+                FIRST_4V_2ND = 0x01U,                   //!< First 4V Second non-SACCH Burst on Slot
+                FIRST_4V_3RD = 0x02U,                   //!< First 4V Third non-SACCH Burst on Slot
+                FIRST_4V_4TH = 0x03U,                   //!< First 4V Fourth non-SACCH Burst on Slot
+                FIRST_4V_5TH = 0x04U,                   //!< First 4V Fifth non-SACCH Burst on Slot
+                FIRST_4V_6TH = 0x05U,                   //!< First 4V Sixth non-SACCH Burst on Slot (Inbound Reserved)
+
+                INBOUND_RANDOM_SACCH = 0x06U,           //!< Inbound Random SACCH (Outbound Reserved)
+
+                NO_VOICE_OR_UNK = 0x07U                 //!< No Voice or Unknown
+            };
+        }
+
         // TIA-102.BBAD-D Section 3
         /** @brief Phase 2 MAC MCO Partitioning */
         namespace P2_MAC_MCO_PARTITION {

src/common/p25/Sync.cpp

@@ -5,7 +5,7 @@
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  *  Copyright (C) 2015,2016 Jonathan Naylor, G4KLX
- *  Copyright (C) 2024 Bryan Biedenkapp, N2PLL
+ *  Copyright (C) 2024,2026 Bryan Biedenkapp, N2PLL
  *
  */
 #include "Defines.h"
@@ -30,3 +30,17 @@ void Sync::addP25Sync(uint8_t* data)
 
     ::memcpy(data, P25_SYNC_BYTES, P25_SYNC_LENGTH_BYTES);
 }
+
+/* Helper to append P25 Phase 2 S-OEMI sync bytes to the passed buffer. */
+
+void Sync::addP25P2_SOEMISync(uint8_t* data)
+{
+    assert(data != nullptr);
+
+    for (uint32_t i = 0U; i < P25_P2_OEMI_SYNC_LENGTH_BITS; i++) {
+        uint32_t n = i + 4U + 134U; // this skips the 4 bits of the DUID and remaining 134 bits of Field 1 and 2 for
+                                    // a S-OEMI
+        bool b = READ_BIT(P25_P2_OEMI_SYNC_BYTES, i);
+        WRITE_BIT(data, n, b);
+    }
+}

src/common/p25/Sync.h

@@ -5,6 +5,7 @@
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  *  Copyright (C) 2015,2016 Jonathan Naylor, G4KLX
+ *  Copyright (C) 2026 Bryan Biedenkapp, N2PLL
  *
  */
 /**
@@ -35,6 +36,12 @@ namespace p25
          * @param data Buffer to append P25 sync bytes to.
          */
         static void addP25Sync(uint8_t* data);
+
+        /**
+         * @brief Helper to append P25 Phase 2 S-OEMI sync bytes to the passed buffer.
+         * @param data Buffer to append P25 Phase 2 OEMI sync bytes to.
+         */
+        static void addP25P2_SOEMISync(uint8_t* data);
     };
 } // namespace p25