First woring AX.25 decoder (in simulation).

AX25Demodulator.cpp

@@ -21,27 +21,27 @@
 #include "Globals.h"
 #include "AX25Demodulator.h"
 
-const float32_t DELAY       = 0.000448F;
 const float32_t SAMPLE_RATE = 24000.0F;
 const float32_t SYMBOL_RATE = 1200.0F;
 
-const uint16_t DELAY_LEN = uint16_t((DELAY / (1.0F / SAMPLE_RATE)) + 0.5F);
+const uint16_t DELAY_LEN = 11U;
 
 const float32_t SAMPLES_PER_SYMBOL = SAMPLE_RATE / SYMBOL_RATE;
 const float32_t PLL_LIMIT          = SAMPLES_PER_SYMBOL / 2.0F;
 
-// XXX This is for the wrong sample rate
 const uint32_t LPF_FILTER_LEN = 96U;
 
 q15_t LPF_FILTER_COEFFS[] = {
-    0,     1,     3,     5,     8,    11,    14,    17,    19,    20,    18,    14,
+     0,    0,    0,    1,    2,    5,    8,   12,   18,   23,
-    7,    -2,   -16,   -33,   -53,   -76,  -101,  -126,  -151,  -174,  -194,  -208,
+    29,   33,   36,   36,   33,   25,   13,   -5,  -28,  -57,
- -215,  -212,  -199,  -173,  -133,   -79,   -10,    74,   173,   287,   413,   549,
+   -89, -123, -159, -194, -225, -249, -264, -267, -254, -224,
-  693,   842,   993,  1142,  1287,  1423,  1547,  1656,  1747,  1817,  1865,  1889,
+  -175, -104,  -12,  102,  236,  389,  557,  738,  926, 1117,
- 1889,  1865,  1817,  1747,  1656,  1547,  1423,  1287,  1142,   993,   842,   693,
+  1306, 1486, 1654, 1802, 1927, 2025, 2092, 2126, 2126, 2092,
-  549,   413,   287,   173,    74,   -10,   -79,  -133,  -173,  -199,  -212,  -215,
+  2025, 1927, 1802, 1654, 1486, 1306, 1117,  926,  738,  557,
- -208,  -194,  -174,  -151,  -126,  -101,   -76,   -53,   -33,   -16,    -2,     7,
+   389,  236,  102,  -12, -104, -175, -224, -254, -267, -264,
-   14,    18,    20,    19,    17,    14,    11,     8,     5,     3,     1,     0,
+  -249, -225, -194, -159, -123,  -89,  -57,  -28,   -5,   13,
+    25,   33,   36,   36,   33,   29,   23,   18,   12,    8,
+     5,    2,    1,    0,    0,    0
 };
 
 // 64 Hz loop filter.
@@ -53,7 +53,7 @@ const uint32_t PLL_FILTER_LEN = 7U;
 
 float32_t PLL_FILTER_COEFFS[] = {3.196252e-02F, 1.204223e-01F, 2.176819e-01F, 2.598666e-01F, 2.176819e-01F, 1.204223e-01F, 3.196252e-02F};
 
-CAX25Demodulator::CAX25Demodulator(float32_t* coeffs, uint16_t length) :
+CAX25Demodulator::CAX25Demodulator(q15_t* coeffs, uint16_t length) :
 m_frame(),
 m_audioFilter(),
 m_audioState(),
@@ -73,7 +73,7 @@ m_hdlcBuffer(0U),
 m_hdlcBits(0U),
 m_hdlcState(AX25_IDLE)
 {
-  m_delayLine = new bool[2U * DELAY_LEN];
+  m_delayLine = new bool[DELAY_LEN];
 
   m_audioFilter.numTaps = length;
   m_audioFilter.pState  = m_audioState;
@@ -88,21 +88,16 @@ m_hdlcState(AX25_IDLE)
   m_pllFilter.pCoeffs = PLL_FILTER_COEFFS;
 }
 
-bool CAX25Demodulator::process(const q15_t* samples, uint8_t length, CAX25Frame& frame)
+bool CAX25Demodulator::process(q15_t* samples, uint8_t length, CAX25Frame& frame)
 {
   bool result = false;
 
-  float32_t input[RX_BLOCK_SIZE];
+  q15_t fa[RX_BLOCK_SIZE];
-  for (size_t i = 0; i < length; i++)
+  ::arm_fir_fast_q15(&m_audioFilter, samples, fa, RX_BLOCK_SIZE);
-    input[i] = float(samples[i]);
-
-  float32_t fa[RX_BLOCK_SIZE];
-  ::arm_fir_f32(&m_audioFilter, input, fa, RX_BLOCK_SIZE);
 
   int16_t buffer[RX_BLOCK_SIZE];
   for (uint8_t i = 0; i < length; i++) {
-      int16_t sample = int16_t(fa[i]);
+      bool   level = (fa[i] >= 0);
-      bool     level = (sample >= 0);
       bool delayed = delay(level);
       buffer[i] = (int16_t(level ^ delayed) << 1) - 1;
   }
@@ -124,7 +119,7 @@ bool CAX25Demodulator::process(const q15_t* samples, uint8_t length, CAX25Frame&
         if (result) {
           // Copy the frame data.
           ::memcpy(frame.m_data, m_frame.m_data, AX25_MAX_PACKET_LEN);
-          frame.m_length = frame.m_length;
+          frame.m_length = m_frame.m_length;
           frame.m_fcs    = m_frame.m_fcs;
           m_frame.m_length = 0U;
         }
@@ -160,7 +155,7 @@ bool CAX25Demodulator::PLL(bool input)
 {
   bool sample = false;
 		
-  if (input != m_pllLast or m_pllBits > 16U) {
+  if (input != m_pllLast || m_pllBits > 16U) {
     // Record transition.
     m_pllLast = input;
 
@@ -214,10 +209,12 @@ bool CAX25Demodulator::HDLC(bool b)
 
     switch (m_hdlcBuffer) {
       case 0x7E:
-        if (m_frame.m_length > 2U) {
+        if (m_frame.m_length >= 13U) {
           result = m_frame.checkCRC();
           if (!result)
               m_frame.m_length = 0U;
+        } else {
+            m_frame.m_length = 0U;
         }
         m_hdlcState = AX25_SYNC;
         m_hdlcFlag = false;

AX25Demodulator.h

@@ -31,21 +31,21 @@ enum AX25_STATE {
 
 class CAX25Demodulator {
 public:
-  CAX25Demodulator(float32_t* coeffs, uint16_t length);
+  CAX25Demodulator(q15_t* coeffs, uint16_t length);
 
-  bool process(const q15_t* samples, uint8_t length, CAX25Frame& frame);
+  bool process(q15_t* samples, uint8_t length, CAX25Frame& frame);
 
 private:
   CAX25Frame           m_frame;
-  arm_fir_instance_f32 m_audioFilter;
+  arm_fir_instance_q15 m_audioFilter;
-  float32_t            m_audioState[20U];
+  q15_t                m_audioState[40U];   // NoTaps + BlockSize - 1, 9 + 20 - 1 plus some spare
   arm_fir_instance_q15 m_lpfFilter;
   q15_t                m_lpfState[120U];    // NoTaps + BlockSize - 1, 96 + 20 - 1 plus some spare
   bool*                m_delayLine;
   uint16_t             m_delayPos;
   bool                 m_nrziState;
   arm_fir_instance_f32 m_pllFilter;
-  float32_t            m_pllState[7U];
+  float32_t            m_pllState[20U];     // NoTaps + BlockSize - 1, 7 + 1 - 1 plus some spare
   bool                 m_pllLast;
   uint8_t              m_pllBits;
   float32_t            m_pllCount;

AX25Frame.cpp

@@ -21,38 +21,38 @@
 #include "AX25Frame.h"
 
 const uint16_t CCITT_TABLE[] = {
-	0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
+	0x0000,0x1189,0x2312,0x329b,0x4624,0x57ad,0x6536,0x74bf,
-	0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
+	0x8c48,0x9dc1,0xaf5a,0xbed3,0xca6c,0xdbe5,0xe97e,0xf8f7,
-	0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
+	0x1081,0x0108,0x3393,0x221a,0x56a5,0x472c,0x75b7,0x643e,
-	0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
+	0x9cc9,0x8d40,0xbfdb,0xae52,0xdaed,0xcb64,0xf9ff,0xe876,
-	0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
+	0x2102,0x308b,0x0210,0x1399,0x6726,0x76af,0x4434,0x55bd,
-	0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
+	0xad4a,0xbcc3,0x8e58,0x9fd1,0xeb6e,0xfae7,0xc87c,0xd9f5,
-	0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
+	0x3183,0x200a,0x1291,0x0318,0x77a7,0x662e,0x54b5,0x453c,
-	0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
+	0xbdcb,0xac42,0x9ed9,0x8f50,0xfbef,0xea66,0xd8fd,0xc974,
-	0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
+	0x4204,0x538d,0x6116,0x709f,0x0420,0x15a9,0x2732,0x36bb,
-	0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
+	0xce4c,0xdfc5,0xed5e,0xfcd7,0x8868,0x99e1,0xab7a,0xbaf3,
-	0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,
+	0x5285,0x430c,0x7197,0x601e,0x14a1,0x0528,0x37b3,0x263a,
-	0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
+	0xdecd,0xcf44,0xfddf,0xec56,0x98e9,0x8960,0xbbfb,0xaa72,
-	0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,
+	0x6306,0x728f,0x4014,0x519d,0x2522,0x34ab,0x0630,0x17b9,
-	0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
+	0xef4e,0xfec7,0xcc5c,0xddd5,0xa96a,0xb8e3,0x8a78,0x9bf1,
-	0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
+	0x7387,0x620e,0x5095,0x411c,0x35a3,0x242a,0x16b1,0x0738,
-	0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,
+	0xffcf,0xee46,0xdcdd,0xcd54,0xb9eb,0xa862,0x9af9,0x8b70,
-	0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
+	0x8408,0x9581,0xa71a,0xb693,0xc22c,0xd3a5,0xe13e,0xf0b7,
-	0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
+	0x0840,0x19c9,0x2b52,0x3adb,0x4e64,0x5fed,0x6d76,0x7cff,
-	0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,
+	0x9489,0x8500,0xb79b,0xa612,0xd2ad,0xc324,0xf1bf,0xe036,
-	0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
+	0x18c1,0x0948,0x3bd3,0x2a5a,0x5ee5,0x4f6c,0x7df7,0x6c7e,
-	0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
+	0xa50a,0xb483,0x8618,0x9791,0xe32e,0xf2a7,0xc03c,0xd1b5,
-	0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
+	0x2942,0x38cb,0x0a50,0x1bd9,0x6f66,0x7eef,0x4c74,0x5dfd,
-	0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,
+	0xb58b,0xa402,0x9699,0x8710,0xf3af,0xe226,0xd0bd,0xc134,
-	0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
+	0x39c3,0x284a,0x1ad1,0x0b58,0x7fe7,0x6e6e,0x5cf5,0x4d7c,
-	0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
+	0xc60c,0xd785,0xe51e,0xf497,0x8028,0x91a1,0xa33a,0xb2b3,
-	0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3,
+	0x4a44,0x5bcd,0x6956,0x78df,0x0c60,0x1de9,0x2f72,0x3efb,
-	0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
+	0xd68d,0xc704,0xf59f,0xe416,0x90a9,0x8120,0xb3bb,0xa232,
-	0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,
+	0x5ac5,0x4b4c,0x79d7,0x685e,0x1ce1,0x0d68,0x3ff3,0x2e7a,
-	0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,
+	0xe70e,0xf687,0xc41c,0xd595,0xa12a,0xb0a3,0x8238,0x93b1,
-	0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,
+	0x6b46,0x7acf,0x4854,0x59dd,0x2d62,0x3ceb,0x0e70,0x1ff9,
-	0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
+	0xf78f,0xe606,0xd49d,0xc514,0xb1ab,0xa022,0x92b9,0x8330,
-	0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0};
+	0x7bc7,0x6a4e,0x58d5,0x495c,0x3de3,0x2c6a,0x1ef1,0x0f78 };
 
 CAX25Frame::CAX25Frame() :
 m_data(),

AX25RX.cpp

@@ -20,47 +20,255 @@
 #include "Globals.h"
 #include "AX25RX.h"
 
-// XXX There are for the wrong sample rate
+// 1200Hz = -12dB, 2200Hz = 0dB; 3381Hz cutoff; cosine.
+q15_t dB12[] = {
+  176,
+  -812,
+  -3916,
+  -7586,
+  23536,
+  -7586,
+  -3916,
+  -812,
+  176
+};
 
-// 1200Hz = -9dB, 2200Hz = 0dB; 3252Hz cutoff, 3.7 gain; cosine.
+// 1200Hz = -11dB, 2200Hz = 0dB; 3258Hz cutoff; cosine.
-float32_t dB9[] = {
+q15_t dB11[] = {
-        -0.00232554104135,
+  121,
-        -0.142858725752,
+  -957,
-        -0.449053780255,
+  -3959,
-        -0.770264863826,
+  -7383,
-        2.77651146344,
+  23871,
-        -0.770264863826,
+  -7383,
-        -0.449053780255,
+  -3959,
-        -0.142858725752,
+  -957,
-        -0.00232554104135};
+  121
+};
 
-// 1200Hz = -6dB, 2200Hz = 0dB; 2640Hz cutoff, 2.59 gain; cosine.
+// 1200Hz = -10dB, 2200Hz = 0dB; 3118Hz cutoff; cosine.
-float32_t dB6[] = {
+q15_t dB10[] = {
-        -0.0209448226653,
+  56,
-        -0.130107651829,
+  -1110,
-        -0.299004731072,
+  -3987,
-        -0.45336946386,
+  -7141,
-        2.0629448761,
+  24254,
-        -0.45336946386,
+  -7141,
-        -0.299004731072,
+  -3987,
-        -0.130107651829,
+  -1110,
-        -0.0209448226653};
+  56
+};
 
-// 1200Hz = -3dB, 2200Hz = 0dB; 1700Hz cutoff, 1.68 gain; cosine.
+// 1200Hz = -9dB, 2200Hz = 0dB; 2959Hz cutoff; cosine.
-float32_t dB3[] = {
+q15_t dB9[] = {
-        -0.0231416146776,
+  -19,
-        -0.0833375337803,
+  -1268,
-        -0.147937602401,
+  -3994,
-        -0.197411259519,
+  -6856,
-        1.46066084756,
+  24688,
-        -0.197411259519,
+  -6856,
-        -0.147937602401,
+  -3994,
-        -0.0833375337803,
+  -1268,
-        -0.0231416146776};
+  -19
+};
+
+// 1200Hz = -8dB, 2200Hz = 0dB; 2778Hz cutoff; cosine.
+q15_t dB8[] = {
+  -104,
+  -1424,
+  -3968,
+  -6516,
+  25182,
+  -6516,
+  -3968,
+  -1424,
+  -104
+};
+
+// 1200Hz = -7dB, 2200Hz = 0dB; 2573Hz cutoff; cosine.
+q15_t dB7[] = {
+  -196,
+  -1565,
+  -3896,
+  -6114,
+  25742,
+  -6114,
+  -3896,
+  -1565,
+  -196
+};
+
+// 1200Hz = -6dB, 2200Hz = 0dB; 2343Hz cutoff; cosine.
+q15_t dB6[] = {
+  -288,
+  -1676,
+  -3761,
+  -5642,
+  26370,
+  -5642,
+  -3761,
+  -1676,
+  -288
+};
+
+// 1200Hz = -5dB, 2200Hz = 0dB; 2085Hz cutoff; cosine.
+q15_t dB5[] = {
+  -370,
+  -1735,
+  -3545,
+  -5088,
+  27075,
+  -5088,
+  -3545,
+  -1735,
+  -370
+};
+
+// 1200Hz = -4dB, 2200Hz = 0dB; 1790Hz cutoff; cosine.
+q15_t dB4[] = {
+  -432,
+  -1715,
+  -3220,
+  -4427,
+  27880,
+  -4427,
+  -3220,
+  -1715,
+  -432
+};
+
+// 1200Hz = -3dB, 2200Hz = 0dB; 1456Hz cutoff; cosine.
+q15_t dB3[] = {
+  -452,
+  -1582,
+  -2759,
+  -3646,
+  28792,
+  -3646,
+  -2759,
+  -1582,
+  -452
+};
+
+// 1200Hz = -2dB, 2200Hz = 0dB; 1070Hz cutoff; cosine.
+q15_t dB2[] = {
+  -408,
+  -1295,
+  -2123,
+  -2710,
+  29846,
+  -2710,
+  -2123,
+  -1295,
+  -408
+};
+
+// 1200Hz = -1dB, 2200Hz = 0dB; 605Hz cutoff; cosine.
+q15_t dB1[] = {
+  -268,
+  -795,
+  -1244,
+  -1546,
+  31116,
+  -1546,
+  -1244,
+  -795,
+  -268
+};
+
+q15_t dB0[] = {
+  0,
+  0,
+  0,
+  0,
+  32767,
+  0,
+  0,
+  0,
+  0,
+};
+
+// 1200Hz = 0dB, 2200Hz = -1dB; 4130Hz cutoff; cosine.
+q15_t dB_1[] = {
+  -419,
+  -177,
+  3316,
+  8650,
+  11278,
+  8650,
+  3316,
+  -177,
+  -419
+};
+
+// 1200Hz = 0dB, 2200Hz = -2dB; 3190Hz cutoff; cosine.
+q15_t dB_2[] = {
+  -90,
+  1033,
+  3975,
+  7267,
+  8711,
+  7267,
+  3975,
+  1033,
+  -90
+};
+
+// 1200Hz = 0dB, 2200Hz = -3dB; 2330Hz cutoff; cosine.
+q15_t dB_3[] = {
+  292,
+  1680,
+  3752,
+  5615,
+  6362,
+  5615,
+  3752,
+  1680,
+  292
+};
+
+// 1200Hz = 0dB, 2200Hz = -4dB; 2657Hz cutoff; boxcar.
+q15_t dB_4[] = {
+  917,
+  3024,
+  5131,
+  6684,
+  7255,
+  6684,
+  5131,
+  3024,
+  917
+};
+
+// 1200Hz = 0dB, 2200Hz = -5dB; 2360Hz cutoff; boxcar.
+q15_t dB_5[] = {
+  1620,
+  3339,
+  4925,
+  6042,
+  6444,
+  6042,
+  4925,
+  3339,
+  1620
+};
+
+// 1200Hz = 0dB, 2200Hz = -6dB; 2067Hz cutoff; boxcar.
+q15_t dB_6[] = {
+  2161,
+  3472,
+  4605,
+  5373,
+  5644,
+  5373,
+  4605,
+  3472,
+  2161
+};
 
 /*
  * Generated with Scipy Filter, 152 coefficients, 1100-2300Hz bandpass,
- * Hann window.
+ * Hann window, starting and ending 0 value coefficients removed.
  *
  * np.array(
  *  firwin2(152,
@@ -77,24 +285,23 @@ float32_t dB3[] = {
  *      window='hann') * 32768,
  *  dtype=int)[10:-10]
  */
-const uint32_t FILTER_LEN = 132U;
+const uint32_t FILTER_LEN = 132;
-
 q15_t FILTER_COEFFS[] = {
-           0,     5,    12,    18,    21,    19,    11,    -2,   -15,
+      0,     5,    12,    18,    21,   19,   11,    -2,   -15,   -25,
-         -25,   -27,   -21,   -11,    -3,    -5,   -19,   -43,   -69,
+    -27,   -21,   -11,    -3,    -5,  -19,  -43,   -69,   -83,   -73,
-         -83,   -73,   -35,    27,    98,   155,   180,   163,   109,
+    -35,    27,    98,   155,   180,  163,  109,    39,   -20,   -45,
-          39,   -20,   -45,   -26,    23,    74,    89,    39,   -81,
+    -26,    23,    74,    89,    39,  -81, -247,  -407,  -501,  -480,
-        -247,  -407,  -501,  -480,  -334,   -92,   175,   388,   479,
+   -334,   -92,   175,   388,   479,  429,  275,    99,     5,    68,
-         429,   275,    99,     5,    68,   298,   626,   913,   994,
+    298,   626,   913,   994,   740,  115, -791, -1770, -2544, -2847,
-         740,   115,  -791, -1770, -2544, -2847, -2509, -1527,   -76,
+  -2509, -1527,   -76,  1518,  2875, 3653, 3653,  2875,  1518,   -76,
-        1518,  2875,  3653,  3653,  2875,  1518,   -76, -1527, -2509,
+  -1527, -2509, -2847, -2544, -1770, -791,  115,   740,   994,   913,
-       -2847, -2544, -1770,  -791,   115,   740,   994,   913,   626,
+    626,   298,    68,     5,    99,  275,  429,   479,   388,   175,
-         298,    68,     5,    99,   275,   429,   479,   388,   175,
+    -92,  -334,  -480,  -501,  -407, -247,  -81,    39,    89,    74,
-         -92,  -334,  -480,  -501,  -407,  -247,   -81,    39,    89,
+     23,   -26,   -45,   -20,    39,  109,  163,   180,   155,    98,
-          74,    23,   -26,   -45,   -20,    39,   109,   163,   180,
+     27,   -35,   -73,   -83,   -69,  -43,  -19,    -5,    -3,   -11,
-         155,    98,    27,   -35,   -73,   -83,   -69,   -43,   -19,
+    -21,   -27,   -25,   -15,    -2,   11,   19,    21,    18,    12,
-          -5,    -3,   -11,   -21,   -27,   -25,   -15,    -2,    11,
+      5,     0
-          19,    21,    18,    12,     5,     0};
+};
 
 CAX25RX::CAX25RX() :
 m_filter(),
@@ -114,33 +321,28 @@ void CAX25RX::samples(q15_t* samples, uint8_t length)
   q15_t output[RX_BLOCK_SIZE];
   ::arm_fir_fast_q15(&m_filter, samples, output, RX_BLOCK_SIZE);
 
+  m_lastFCS = 0U;
   CAX25Frame frame;
 
   bool ret = m_demod1.process(output, length, frame);
-  if (ret && frame.m_length > 10U) {
+  if (ret && frame.m_fcs != m_lastFCS) {
-    if (m_lastFCS != frame.m_fcs) {
     DEBUG1("Decoder 1 reported");
     m_lastFCS = frame.m_fcs;
     serial.writeAX25Data(frame.m_data, frame.m_length - 2U);
   }
-  }
 
   ret = m_demod2.process(output, length, frame);
-  if (ret && frame.m_length > 10U) {
+  if (ret && frame.m_fcs != m_lastFCS) {
-    if (m_lastFCS != frame.m_fcs) {
     DEBUG1("Decoder 2 reported");
     m_lastFCS = frame.m_fcs;
     serial.writeAX25Data(frame.m_data, frame.m_length - 2U);
   }
-  }
 
   ret = m_demod3.process(output, length, frame);
-  if (ret && frame.m_length > 10U) {
+  if (ret && frame.m_fcs != m_lastFCS) {
-    if (m_lastFCS != frame.m_fcs) {
     DEBUG1("Decoder 3 reported");
     m_lastFCS = frame.m_fcs;
     serial.writeAX25Data(frame.m_data, frame.m_length - 2U);
   }
 }
-}