3 files changed, 219 insertions, 0 deletions
diff --git a/gr-digital/lib/Makefile.am b/gr-digital/lib/Makefile.am
index 3d39d15dac..acefa1ef9c 100644
--- a/gr-digital/lib/Makefile.am
+++ b/gr-digital/lib/Makefile.am
@@ -31,6 +31,7 @@ grinclude_HEADERS = 				\
 	digital_constellation.h			\
 	digital_constellation_receiver_cb.h 	\
 	digital_constellation_decoder_cb.h 	\
+	digital_correlate_access_code_bb.h	\
 	digital_costas_loop_cc.h		\
 	digital_cma_equalizer_cc.h		\
 	digital_lms_dd_equalizer_cc.h		\
@@ -46,6 +47,7 @@ libgnuradio_digital_la_SOURCES = 		\
 	digital_constellation.cc		\
 	digital_constellation_receiver_cb.cc	\
 	digital_constellation_decoder_cb.cc	\
+	digital_correlate_access_code_bb.cc	\
 	digital_costas_loop_cc.cc		\
 	digital_cma_equalizer_cc.cc		\
 	digital_lms_dd_equalizer_cc.cc		\
diff --git a/gr-digital/lib/digital_correlate_access_code_bb.cc b/gr-digital/lib/digital_correlate_access_code_bb.cc
new file mode 100644
index 0000000000..f21b57d92c
--- /dev/null
+++ b/gr-digital/lib/digital_correlate_access_code_bb.cc
@@ -0,0 +1,134 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2004,2006,2010,2011 Free Software Foundation, Inc.
+ * 
+ * This file is part of GNU Radio
+ * 
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ * 
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <digital_correlate_access_code_bb.h>
+#include <gr_io_signature.h>
+#include <stdexcept>
+#include <gr_count_bits.h>
+#include <cstdio>
+
+
+#define VERBOSE 0
+
+
+digital_correlate_access_code_bb_sptr
+digital_make_correlate_access_code_bb (const std::string &access_code, int threshold)
+{
+  return gnuradio::get_initial_sptr(new digital_correlate_access_code_bb
+				    (access_code, threshold));
+}
+
+
+digital_correlate_access_code_bb::digital_correlate_access_code_bb (
+  const std::string &access_code, int threshold)
+  : gr_sync_block ("correlate_access_code_bb",
+		   gr_make_io_signature (1, 1, sizeof(char)),
+		   gr_make_io_signature (1, 1, sizeof(char))),
+    d_data_reg(0), d_flag_reg(0), d_flag_bit(0), d_mask(0),
+    d_threshold(threshold)
+
+{
+  if (!set_access_code(access_code)){
+    fprintf(stderr, "digital_correlate_access_code_bb: access_code is > 64 bits\n");
+    throw std::out_of_range ("access_code is > 64 bits");
+  }
+}
+
+digital_correlate_access_code_bb::~digital_correlate_access_code_bb ()
+{
+}
+
+bool
+digital_correlate_access_code_bb::set_access_code(
+  const std::string &access_code)
+{
+  unsigned len = access_code.length();	// # of bytes in string
+  if (len > 64)
+    return false;
+
+  // set len top bits to 1.
+  d_mask = ((~0ULL) >> (64 - len)) << (64 - len);
+
+  d_flag_bit = 1LL << (64 - len);	// Where we or-in new flag values.
+                                        // new data always goes in 0x0000000000000001
+  d_access_code = 0;
+  for (unsigned i=0; i < 64; i++){
+    d_access_code <<= 1;
+    if (i < len)
+      d_access_code |= access_code[i] & 1;	// look at LSB only
+  }
+
+  return true;
+}
+
+int
+digital_correlate_access_code_bb::work (int noutput_items,
+					gr_vector_const_void_star &input_items,
+					gr_vector_void_star &output_items)
+{
+  const unsigned char *in = (const unsigned char *) input_items[0];
+  unsigned char *out = (unsigned char *) output_items[0];
+
+  for (int i = 0; i < noutput_items; i++){
+
+    // compute output value
+    unsigned int t = 0;
+
+    t |= ((d_data_reg >> 63) & 0x1) << 0;
+    t |= ((d_flag_reg >> 63) & 0x1) << 1;	// flag bit
+    out[i] = t;
+    
+    // compute hamming distance between desired access code and current data
+    unsigned long long wrong_bits = 0;
+    unsigned int nwrong = d_threshold+1;
+    int new_flag = 0;
+
+    wrong_bits  = (d_data_reg ^ d_access_code) & d_mask;
+    nwrong = gr_count_bits64(wrong_bits);
+
+    // test for access code with up to threshold errors
+    new_flag = (nwrong <= d_threshold);
+
+#if VERBOSE
+    if(new_flag) {
+      fprintf(stderr, "access code found: %llx\n", d_access_code);
+    }
+    else {
+      fprintf(stderr, "%llx  ==>  %llx\n", d_access_code, d_data_reg);
+    }
+#endif
+
+    // shift in new data and new flag
+    d_data_reg = (d_data_reg << 1) | (in[i] & 0x1);
+    d_flag_reg = (d_flag_reg << 1);
+    if (new_flag) {
+      d_flag_reg |= d_flag_bit;
+    }
+  }
+
+  return noutput_items;
+}
+  
diff --git a/gr-digital/lib/digital_correlate_access_code_bb.h b/gr-digital/lib/digital_correlate_access_code_bb.h
new file mode 100644
index 0000000000..2607ae84c2
--- /dev/null
+++ b/gr-digital/lib/digital_correlate_access_code_bb.h
@@ -0,0 +1,83 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2005,2006,2011 Free Software Foundation, Inc.
+ * 
+ * This file is part of GNU Radio
+ * 
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ * 
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef INCLUDED_DIGITAL_CORRELATE_ACCESS_CODE_BB_H
+#define INCLUDED_DIGITAL_CORRELATE_ACCESS_CODE_BB_H
+
+#include <gr_sync_block.h>
+#include <string>
+
+class digital_correlate_access_code_bb;
+typedef boost::shared_ptr<digital_correlate_access_code_bb> digital_correlate_access_code_bb_sptr;
+
+/*!
+ * \param access_code is represented with 1 byte per bit, e.g., "010101010111000100"
+ * \param threshold maximum number of bits that may be wrong
+ */
+digital_correlate_access_code_bb_sptr 
+digital_make_correlate_access_code_bb (const std::string &access_code, int threshold);
+
+/*!
+ * \brief Examine input for specified access code, one bit at a time.
+ * \ingroup sync_blk
+ *
+ * input:  stream of bits, 1 bit per input byte (data in LSB)
+ * output: stream of bits, 2 bits per output byte (data in LSB, flag in next higher bit)
+ *
+ * Each output byte contains two valid bits, the data bit, and the
+ * flag bit.  The LSB (bit 0) is the data bit, and is the original
+ * input data, delayed 64 bits.  Bit 1 is the
+ * flag bit and is 1 if the corresponding data bit is the first data
+ * bit following the access code. Otherwise the flag bit is 0.
+ */
+class digital_correlate_access_code_bb : public gr_sync_block
+{
+  friend digital_correlate_access_code_bb_sptr 
+  digital_make_correlate_access_code_bb (const std::string &access_code, int threshold);
+ private:
+  unsigned long long d_access_code;	// access code to locate start of packet
+                                        //   access code is left justified in the word
+  unsigned long long d_data_reg;	// used to look for access_code
+  unsigned long long d_flag_reg;	// keep track of decisions
+  unsigned long long d_flag_bit;	// mask containing 1 bit which is location of new flag
+  unsigned long long d_mask;		// masks access_code bits (top N bits are set where
+                                        //   N is the number of bits in the access code)
+  unsigned int	     d_threshold;	// how many bits may be wrong in sync vector
+
+ protected:
+  digital_correlate_access_code_bb(const std::string &access_code, int threshold);
+
+ public:
+  ~digital_correlate_access_code_bb();
+
+  int work(int noutput_items,
+	   gr_vector_const_void_star &input_items,
+	   gr_vector_void_star &output_items);
+
+  
+  /*!
+   * \param access_code is represented with 1 byte per bit, e.g., "010101010111000100"
+   */
+  bool set_access_code (const std::string &access_code);
+};
+
+#endif /* INCLUDED_DIGITAL_CORRELATE_ACCESS_CODE_BB_H */