From d7b36f32c08f3cf55d6c7cdea08a42c9e5329ae8 Mon Sep 17 00:00:00 2001
From: EdFuentetaja <ed.fuentetaja@gmail.com>
Date: Sat, 1 Mar 2014 20:35:46 +0800
Subject: [PATCH] Parity errors in NIC are now ignored. Clean up the code to
 make it easier to understand. Now the logic to error correct the NIC makes
 more sense.

---
 check_nid.cpp       | 109 --------------------------------------------
 check_nid.h         |  14 ------
 dsd.h               |   1 +
 dsd_frame.c         |  29 +++++++-----
 dsd_main.c          |   2 +
 p25p1_check_nid.cpp |  92 +++++++++++++++++++++++++++++++++++++
 p25p1_check_nid.h   |  24 ++++++++++
 7 files changed, 137 insertions(+), 134 deletions(-)
 delete mode 100644 check_nid.cpp
 delete mode 100644 check_nid.h
 create mode 100644 p25p1_check_nid.cpp
 create mode 100644 p25p1_check_nid.h

diff --git a/check_nid.cpp b/check_nid.cpp
deleted file mode 100644
index 299563b..0000000
--- a/check_nid.cpp
+++ /dev/null
@@ -1,109 +0,0 @@
-#include <itpp/itcomm.h>
-
-#include "check_nid.h"
-
-
-
-using namespace itpp;
-
-// Ideas taken from http://op25.osmocom.org/trac/wiki.png/browser/op25/gr-op25/lib/decoder_ff_impl.cc
-// See also p25_training_guide.pdf page 48.
-// See also tia-102-baaa-a-project_25-fdma-common_air_interface.pdf page 40.
-// BCH encoder/decoder implementation from IT++. GNU GPL 3 license.
-
-itpp::BCH bch(63, 16, 11, "6 3 3 1 1 4 1 3 6 7 2 3 5 4 5 3", true);
-
-/** Convenience class to calculate the parity of the DUID values. Keeps a table with the expected outcomes
- * for fast lookup.
- */
-class ParityTable
-{
-private:
-    unsigned char table[16];
-
-    unsigned char get_index(unsigned char x, unsigned char y)
-    {
-        return (x<<2) + y;
-    }
-
-public:
-    ParityTable()
-    {
-        for (unsigned int i=0; i<sizeof(table); i++) {
-            table[i] = 0;
-        }
-        table[get_index(1,1)] = 1;
-        table[get_index(2,2)] = 1;
-    }
-
-    unsigned char get_value(unsigned char x, unsigned char y)
-    {
-        return table[get_index(x,y)];
-    }
-
-} parity_table;
-
-/** Checks a NID value, returns the fixed NAC, DUID and also an indication if it failed to decode the NID.
- *
- *  \param bch_code Input. An array to the 63 bytes, each containing one bit of the NID.
- *  \param new_nac Output. An address where to store the calculated NAC value after error correction. Should
- *                 be large enough to accommodate for an integer.
- *  \param new_duid Output. An address where to store the calculated DUID value after error correction. Should
- *                  be able to accommodate 3 chars.
- *  \param parity Input. The parity value read.
- *  \return 0 if there were errors processing the NID.
- */
-int check_NID(char* bch_code, int* new_nac, char* new_duid, unsigned char parity)
-{
-    int result;
-
-    // Fill up with the input given
-    bvec input(63);
-    for(unsigned int i=0; i<63; i++) {
-        input[i] = bch_code[i];
-    }
-
-    // Decode it
-    bvec decoded = bch.decode(input);
-
-    // Check if the decoded output is zero
-    bool zero = true;
-    for (int i=0; i<decoded.length(); i++) {
-        if (decoded[i] != 0) {
-            zero = false;
-            break;
-        }
-    }
-
-    if (zero) {
-        // Decode failed
-        result = 0;
-    } else {
-        // Encode it again
-        bvec encoded = bch.encode(decoded);
-
-        // Take the fixed NAC from the encoded output. It's a 12 bit number starting from position 47.
-        // Just convert the output from a binary sequence to an integer.
-        int nac = 0;
-        for (int i=47; i<47+12; i++) {
-            nac <<= 1;
-            nac |= (int)encoded[i];
-        }
-        *new_nac = nac;
-
-        // Take the fixed DUID from the encoded output. 4 bit value starting at position 59.
-        unsigned char x = (((int)encoded[59])<<1) + ((int)encoded[60]);
-        unsigned char y = (((int)encoded[61])<<1) + ((int)encoded[62]);
-        new_duid[0] = x + '0';
-        new_duid[1] = y + '0';
-        new_duid[2] = 0;
-
-        // Check the parity
-        unsigned char expected_parity = parity_table.get_value(x,y);
-
-        // Returns false (0) if they don't match
-        result = (expected_parity == parity);
-    }
-
-    return result;
-}
diff --git a/check_nid.h b/check_nid.h
deleted file mode 100644
index 3bc1178..0000000
--- a/check_nid.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#ifndef __CHECK_NID_H__
-#define __CHECK_NID_H__
-
-#ifdef __cplusplus 
-extern "C" {
-#endif
-
-int check_NID(char* bch_code, int* new_nac, char* new_duid, unsigned char parity);
-
-#ifdef __cplusplus 
-}
-#endif
-
-#endif // __CHECK_NID_H__
diff --git a/dsd.h b/dsd.h
index 86b32ed..ad6ffdc 100644
--- a/dsd.h
+++ b/dsd.h
@@ -171,6 +171,7 @@ typedef struct
 
   unsigned int debug_audio_errors;
   unsigned int debug_header_errors;
+  unsigned int debug_header_critical_errors;
 
 } dsd_state;
 
diff --git a/dsd_frame.c b/dsd_frame.c
index ae16cf1..893c367 100644
--- a/dsd_frame.c
+++ b/dsd_frame.c
@@ -20,7 +20,7 @@
 #define NULL 0
 #endif
 
-#include "check_nid.h"
+#include "p25p1_check_nid.h"
 
 void
 printFrameInfo (dsd_opts * opts, dsd_state * state)
@@ -246,9 +246,9 @@ processFrame (dsd_opts * opts, dsd_state * state)
     }
   else
     {
-      // NAC, 12 bits
+      // Read the NAC, 12 bits
       j = 0;
-      index_bch_code = 47;
+      index_bch_code = 0;
       for (i = 0; i < 6; i++)
         {
           dibit = getDibit (opts, state);
@@ -267,7 +267,7 @@ processFrame (dsd_opts * opts, dsd_state * state)
         }
       state->nac = strtol (nac, NULL, 2);
 
-      // DUID, 4 bits
+      // Read the DUID, 4 bits
       for (i = 0; i < 2; i++)
         {
           dibit = getDibit (opts, state);
@@ -279,8 +279,7 @@ processFrame (dsd_opts * opts, dsd_state * state)
           index_bch_code++;
         }
 
-      // Now processing NID
-      index_bch_code = 0;
+      // Read the BCH data for error correction of NAC and DUID
       for (i = 0; i < 3; i++)
         {
           dibit = getDibit (opts, state);
@@ -301,7 +300,7 @@ processFrame (dsd_opts * opts, dsd_state * state)
           index_bch_code++;
         }
 
-      // last bit is the parity bit
+      // Read the parity bit
       dibit = getDibit (opts, state);
       bch_code[index_bch_code] = 1 & (dibit >> 1);      // bit 1
       parity = (1 & dibit);     // bit 0
@@ -316,15 +315,17 @@ processFrame (dsd_opts * opts, dsd_state * state)
           }
           if (strcmp(new_duid, duid) != 0) {
               // DUID fixed by error correction
+              //printf("Fixing DUID %s -> %s\n", duid, new_duid);
               duid[0] = new_duid[0];
               duid[1] = new_duid[1];
               state->debug_header_errors++;
           }
       } else {
           // Check of NID failed and unable to recover its value
+          //printf("NID error\n");
           duid[0] = 'E';
           duid[1] = 'E';
-          state->debug_header_errors += 10;
+          state->debug_header_critical_errors ++;
       }
     }
 
@@ -505,7 +506,9 @@ processFrame (dsd_opts * opts, dsd_state * state)
               openMbeOutFile (opts, state);
             }
         }
-      state->lastp25type = 0;
+      //state->lastp25type = 0;
+      // Guess that the state is LDU2
+      state->lastp25type = 2;
       sprintf (state->fsubtype, "(LDU2)        ");
       state->numtdulc = 0;
       processLDU2 (opts, state);
@@ -524,7 +527,9 @@ processFrame (dsd_opts * opts, dsd_state * state)
               openMbeOutFile (opts, state);
             }
         }
-      state->lastp25type = 0;
+      //state->lastp25type = 0;
+      // Guess that the state is LDU1
+      state->lastp25type = 1;
       sprintf (state->fsubtype, "(LDU1)        ");
       state->numtdulc = 0;
       processLDU1 (opts, state);
@@ -536,7 +541,9 @@ processFrame (dsd_opts * opts, dsd_state * state)
           printFrameInfo (opts, state);
           printf (" (TSDU)\n");
         }
-      state->lastp25type = 0;
+      //state->lastp25type = 0;
+      // Guess that the state is TSDU
+      state->lastp25type = 3;
       sprintf (state->fsubtype, "(TSDU)        ");
 
       // Now processing NID
diff --git a/dsd_main.c b/dsd_main.c
index c1d141b..d59704c 100644
--- a/dsd_main.c
+++ b/dsd_main.c
@@ -223,6 +223,7 @@ initState (dsd_state * state)
 
   state->debug_audio_errors = 0;
   state->debug_header_errors = 0;
+  state->debug_header_critical_errors = 0;
 }
 
 void
@@ -325,6 +326,7 @@ cleanupAndExit (dsd_opts * opts, dsd_state * state)
   printf("\n");
   printf("Total audio errors: %i\n", state->debug_audio_errors);
   printf("Total header errors: %i\n", state->debug_header_errors);
+  printf("Total irrecoverable header errors: %i\n", state->debug_header_critical_errors);
 
   printf ("Exiting.\n");
   exit (0);
diff --git a/p25p1_check_nid.cpp b/p25p1_check_nid.cpp
new file mode 100644
index 0000000..9a4e305
--- /dev/null
+++ b/p25p1_check_nid.cpp
@@ -0,0 +1,92 @@
+#include <itpp/itcomm.h>
+
+#include "p25p1_check_nid.h"
+
+
+
+using namespace itpp;
+
+// Ideas taken from http://op25.osmocom.org/trac/wiki.png/browser/op25/gr-op25/lib/decoder_ff_impl.cc
+// See also p25_training_guide.pdf page 48.
+// See also tia-102-baaa-a-project_25-fdma-common_air_interface.pdf page 40.
+// BCH encoder/decoder implementation from IT++. GNU GPL 3 license.
+
+itpp::BCH bch(63, 16, 11, "6 3 3 1 1 4 1 3 6 7 2 3 5 4 5 3", true);
+
+/** Convenience class to calculate the parity of the DUID values. Keeps a table with the expected outcomes
+ * for fast lookup.
+ */
+class ParityTable
+{
+private:
+    unsigned char table[16];
+
+    unsigned char get_index(unsigned char x, unsigned char y)
+    {
+        return (x<<2) + y;
+    }
+
+public:
+    ParityTable()
+    {
+        for (unsigned int i=0; i<sizeof(table); i++) {
+            table[i] = 0;
+        }
+        table[get_index(1,1)] = 1;
+        table[get_index(2,2)] = 1;
+    }
+
+    unsigned char get_value(unsigned char x, unsigned char y)
+    {
+        return table[get_index(x,y)];
+    }
+
+} parity_table;
+
+int check_NID(char* bch_code, int* new_nac, char* new_duid, unsigned char parity)
+{
+    int result;
+
+    // Fill up with the given input
+    bvec input(63);
+    for(unsigned int i=0; i<63; i++) {
+        input[i] = bch_code[i];
+    }
+
+    // Decode it
+    bvec decoded, cw_isvalid;
+    bool ok = bch.decode(input, decoded, cw_isvalid);
+
+    if (!ok) {
+        // Decode failed
+        result = 0;
+    } else {
+        // Take the NAC from the decoded output. It's a 12 bit number starting from position 0.
+        // Just convert the output from a binary sequence to an integer.
+        int nac = 0;
+        for (int i=0; i<12; i++) {
+            nac <<= 1;
+            nac |= (int)decoded[i];
+        }
+        *new_nac = nac;
+
+        // Take the fixed DUID from the encoded output. 4 bit value starting at position 12.
+        unsigned char new_duid_0 = (((int)decoded[12])<<1) + ((int)decoded[13]);
+        unsigned char new_duid_1 = (((int)decoded[14])<<1) + ((int)decoded[15]);
+        new_duid[0] = new_duid_0 + '0';
+        new_duid[1] = new_duid_1 + '0';
+        new_duid[2] = 0;    // Null terminate
+
+        // Check the parity
+        unsigned char expected_parity = parity_table.get_value(new_duid_0, new_duid_1);
+
+        if (expected_parity != parity) {
+            // Ignore, not sure what to do
+            //printf("Error in parity detected?");
+        }
+
+        result = 1;
+    }
+
+    return result;
+}
diff --git a/p25p1_check_nid.h b/p25p1_check_nid.h
new file mode 100644
index 0000000..70fe08f
--- /dev/null
+++ b/p25p1_check_nid.h
@@ -0,0 +1,24 @@
+#ifndef __CHECK_NID_H__
+#define __CHECK_NID_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** Checks a NID value, returns the fixed NAC, DUID and also an indication if it failed to decode the NID.
+ *
+ *  \param bch_code Input. An array to the 63 bytes, each containing one bit of the NID.
+ *  \param new_nac Output. An address where to store the calculated NAC value after error correction. Should
+ *                 be large enough to accommodate for an integer.
+ *  \param new_duid Output. An address where to store the calculated DUID value after error correction. Should
+ *                  be able to accommodate 3 chars.
+ *  \param parity Input. The parity value read.
+ *  \return 0 if there were errors processing the NID.
+ */
+int check_NID(char* bch_code, int* new_nac, char* new_duid, unsigned char parity);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // __CHECK_NID_H__