Implementation of TCH/F demapper block. See issue #38
diff --git a/lib/demapping/tch_f_chans_demapper_impl.cc b/lib/demapping/tch_f_chans_demapper_impl.cc
new file mode 100644
index 0000000..a2458f1
--- /dev/null
+++ b/lib/demapping/tch_f_chans_demapper_impl.cc
@@ -0,0 +1,188 @@
+/* -*- c++ -*- */
+/*
+ * @file
+ * @author Piotr Krysik <ptrkrysik@gmail.com>
+ * @section LICENSE
+ *
+ * Gr-gsm 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.
+ *
+ * Gr-gsm 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 gr-gsm; 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 <gnuradio/io_signature.h>
+#include "tch_f_chans_demapper_impl.h"
+#include <grgsm/endian.h>
+#include <grgsm/gsmtap.h>
+
+namespace gr {
+ namespace gsm {
+
+ tch_f_chans_demapper::sptr
+ tch_f_chans_demapper::make(unsigned int timeslot_nr)
+ {
+ return gnuradio::get_initial_sptr
+ (new tch_f_chans_demapper_impl(timeslot_nr));
+ }
+
+ /*
+ * The private constructor
+ *
+ */
+ tch_f_chans_demapper_impl::tch_f_chans_demapper_impl(unsigned int timeslot_nr)
+ : gr::block("tch_f_chans_demapper",
+ gr::io_signature::make(0, 0, 0),
+ gr::io_signature::make(0, 0, 0)),
+ d_timeslot(timeslot_nr)
+
+ {
+ for(int ii=0; ii<13; ii++)
+ {
+ int startpos = ((int)(ii / 4) * 4);
+ d_starts_fn_mod26[ii] = startpos;
+ d_starts_fn_mod26[ii + 13] = startpos + 13;
+ }
+
+ d_bursts_stolen = false;
+
+ message_port_register_in(pmt::mp("bursts"));
+ set_msg_handler(pmt::mp("bursts"), boost::bind(&tch_f_chans_demapper_impl::filter_tch_chans, this, _1));
+ message_port_register_out(pmt::mp("tch_bursts"));
+ message_port_register_out(pmt::mp("acch_bursts"));
+ }
+
+ /*
+ * Our virtual destructor.
+ */
+ tch_f_chans_demapper_impl::~tch_f_chans_demapper_impl()
+ {
+ }
+
+ void tch_f_chans_demapper_impl::filter_tch_chans(pmt::pmt_t msg)
+ {
+ pmt::pmt_t header_plus_burst = pmt::cdr(msg);
+ gsmtap_hdr * header = (gsmtap_hdr *)pmt::blob_data(header_plus_burst);
+
+ uint32_t frame_nr = be32toh(header->frame_number);
+ uint32_t fn_mod26 = frame_nr % 26;
+ uint32_t fn26_start = d_starts_fn_mod26[fn_mod26];
+ uint32_t fn26_stop = fn26_start + 3;
+ int8_t * burst_bits = (int8_t *)(pmt::blob_data(header_plus_burst))+sizeof(gsmtap_hdr);
+
+ if(header->timeslot == d_timeslot){
+ header->sub_type = GSMTAP_CHANNEL_TCH_F;
+
+ if (fn_mod26 == 12 || fn_mod26 == 25)
+ {
+ header->sub_type = GSMTAP_CHANNEL_ACCH|GSMTAP_CHANNEL_TCH_F;
+
+ // position of SACCH burst based on timeslot
+ // see specification gsm 05.02
+ uint32_t index;
+ bool is_sacch = false;
+
+ if (d_timeslot % 2 == 0 && fn_mod26 == 12)
+ {
+ index = (((frame_nr - 12) / 26) - (d_timeslot / 2)) % 4;
+ is_sacch = true;
+ }
+ else if (d_timeslot % 2 == 1 && fn_mod26 == 25)
+ {
+ index = (((frame_nr - 25) / 26) - ((d_timeslot - 1) / 2)) % 4;
+ is_sacch = true;
+ }
+
+ if (is_sacch)
+ {
+ d_bursts_sacch[index] = msg;
+ d_frame_numbers_sacch[index] = frame_nr;
+
+ if (index == 3)
+ {
+ //check for a situation where some bursts were lost
+ //in this situation frame numbers won't be consecutive
+ bool frames_are_consecutive = true;
+ for(int jj=1; jj<4; jj++)
+ {
+ if((d_frame_numbers_sacch[jj]-d_frame_numbers_sacch[jj-1]) != 26)
+ {
+ frames_are_consecutive = false;
+ }
+ }
+ if(frames_are_consecutive)
+ {
+ //send bursts to the output
+ for(int jj=0; jj<4; jj++)
+ {
+ message_port_pub(pmt::mp("acch_bursts"), d_bursts_sacch[jj]);
+ }
+ }
+ }
+ }
+ }
+ else
+ {
+ if(fn_mod26>=fn26_start && fn_mod26<=fn26_stop)
+ {
+ uint32_t ii = fn_mod26 - fn26_start;
+ d_frame_numbers[ii] = frame_nr;
+ d_bursts[ii] = msg;
+
+ // check if stealing bits are set
+ // see gsm 05.03
+ if (static_cast<int>(burst_bits[60]) == 1 && static_cast<int>(burst_bits[87]) == 1)
+ {
+ d_bursts_stolen = true;
+ }
+ }
+
+ if(fn_mod26==fn26_stop)
+ {
+ //check for a situation where some bursts were lost
+ //in this situation frame numbers won't be consecutive
+ bool frames_are_consecutive = true;
+
+ for(int jj=1; jj<4; jj++)
+ {
+ if((d_frame_numbers[jj]-d_frame_numbers[jj-1])!=1)
+ {
+ frames_are_consecutive = false;
+ }
+ }
+ if(frames_are_consecutive)
+ {
+ //send bursts to the output
+ for(int jj=0; jj<4; jj++)
+ {
+ if (d_bursts_stolen)
+ {
+ message_port_pub(pmt::mp("acch_bursts"), d_bursts[jj]);
+ }
+ else
+ {
+ message_port_pub(pmt::mp("tch_bursts"), d_bursts[jj]);
+ }
+ }
+ d_bursts_stolen = false;
+ }
+ }
+ }
+ }
+ }
+ } /* namespace gsm */
+} /* namespace gr */
+