More framework.

src/CMakeLists.txt

@@ -85,6 +85,7 @@ list(APPEND direwolf_SOURCES
   dwgpsnmea.c
   dwgpsd.c
   mheard.c
+  eotd.c
   )
 
 if(LINUX)
@@ -317,6 +318,7 @@ list(APPEND atest_SOURCES
   symbols.c
   tt_text.c
   textcolor.c
+  eotd.c
   )
 
 if(WIN32 OR CYGWIN)

src/eotd.c

@@ -0,0 +1,69 @@
+
+//    This file is part of Dire Wolf, an amateur radio packet TNC.
+//
+//    Copyright (C) 2022  David Tiller, K4DET
+//
+//    This program 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 2 of the License, or
+//    (at your option) any later version.
+//
+//    This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+
+/********************************************************************************
+ *
+ * File:	eotd.c
+ *
+ * Purpose:	Functions for processing received EOTD transmissions and
+ *		converting to NMEA sentence representation.
+ *
+ * References:	AIVDM/AIVDO protocol decoding by Eric S. Raymond
+ *		https://gpsd.gitlab.io/gpsd/AIVDM.html
+ *
+ *		Sample recording with about 100 messages.  Test with "atest -B AIS xxx.wav"
+ *		https://github.com/freerange/ais-on-sdr/wiki/example-data/long-beach-160-messages.wav
+ *
+ *		Useful on-line decoder for AIS NMEA sentences.
+ *		https://www.aggsoft.com/ais-decoder.htm
+ *
+ * Future?	Add an interface to feed AIS data into aprs.fi.
+ *		https://aprs.fi/page/ais_feeding
+ *		
+ *******************************************************************************/
+
+#include "direwolf.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <ctype.h>
+#include <string.h>
+
+#include "textcolor.h"
+#include "eotd.h"
+
+/*-------------------------------------------------------------------
+ *
+ * Convert EOTD binary block (from HDLC frame) to NMEA sentence. 
+ *
+ * In:	Pointer to EOTD binary block and number of bytes.
+ * Out:	NMEA sentence.  Provide size to avoid string overflow.
+ *
+ *--------------------------------------------------------------------*/
+
+void eotd_to_nmea (unsigned char *eotd, int eotd_len, char *nmea, int nmea_size)
+{
+	for (int i = 0; i < eotd_len; i++) {
+		char temp[32];
+		snprintf(temp, sizeof(temp), "%d=%02x ", i, eotd[i]);
+		strlcpy(nmea, temp, nmea_size);
+	}
+}

src/eotd.h

@@ -0,0 +1 @@
+void eotd_to_nmea (unsigned char *ais, int ais_len, char *nema, int nema_size);

src/hdlc_rec.c

@@ -1,5 +1,5 @@
-//
-//    This file is part of Dire Wolf, an amateur radio packet TNC.
+////
+////    This file is part of Dire Wolf, an amateur radio packet TNC.
 //
 //    Copyright (C) 2011, 2012, 2013, 2014, 2015  John Langner, WB2OSZ
 //
@@ -111,6 +111,10 @@ struct hdlc_state_s {
 	int eas_plus_found;		/* "+" seen, indicating end of geographical area list. */
 
 	int eas_fields_after_plus;	/* Number of "-" characters after the "+". */
+
+	uint32_t eotd_acc;		/* Accumulate last recent 32 bits for EOTD. */
+
+	int eotd_gathering;		/* Decoding in progress - valid frame. */
 };
 
 static struct hdlc_state_s hdlc_state[MAX_CHANS][MAX_SUBCHANS][MAX_SLICERS];
@@ -423,6 +427,8 @@ a good modem here and providing a result when it is received.
  *
  ***********************************************************************************/
 
+#define PREAMBLE_AND_BARKER_CODE	0x55555712
+#define EOTD_MAX_LEN			8
 
 static void eotd_rec_bit (int chan, int subchan, int slice, int raw, int future_use)
 {
@@ -432,7 +438,59 @@ static void eotd_rec_bit (int chan, int subchan, int slice, int raw, int future_
  * Different state information for each channel / subchannel / slice.
  */
 	H = &hdlc_state[chan][subchan][slice];
+
 fprintf(stderr, "chan=%d subchan=%d slice=%d raw=%d\n", chan, subchan, slice, raw);
+	  //dw_printf ("slice %d = %d\n", slice, raw);
+
+// Accumulate most recent 32 bits in MSB-first order.
+
+	H->eotd_acc <<= 1;
+	H->eotd_acc |= raw;
+
+	int done = 0;
+
+	if (!H->eotd_gathering && H->eotd_acc == PREAMBLE_AND_BARKER_CODE) {
+	  dw_printf ("Barker Code Found\n");
+	  H->olen = 0;
+	  H->eotd_gathering = 1;
+	  H->frame_len = 0;
+	}
+	else if (H->eotd_gathering) {
+	  H->olen++;
+	
+	/* Hack to skip 'dummy' 64th bit */
+	  if (H->olen == 7 && H->frame_len == 7) {
+fprintf(stderr, "Special case!\n");
+		H->eotd_acc <<= 1;
+		H->olen++;
+	  }
+
+	  if (H->olen == 8) {
+	    H->olen = 0;
+	    char ch = H->eotd_acc & 0xff;
+	    H->frame_buf[H->frame_len++] = ch;
+	    H->frame_buf[H->frame_len] = '\0';
+	    //dw_printf ("frame_buf = %s\n", H->frame_buf);
+
+	    if (H->frame_len == EOTD_MAX_LEN) {		// FIXME: look for other places with max length
+	      done = 1;
+for (int ii=0; ii < EOTD_MAX_LEN; ii++) {fprintf(stderr, "%02x ", H->frame_buf[ii]); } fprintf(stderr, "\n");
+	    }
+	  }
+	}
+
+	if (done) {
+#ifdef DEBUG_E
+	  dw_printf ("frame_buf %d = %s\n", slice, H->frame_buf);
+#endif
+	  alevel_t alevel = demod_get_audio_level (chan, subchan);
+	  multi_modem_process_rec_frame (chan, subchan, slice, H->frame_buf, H->frame_len, alevel, 0, 0);
+
+	  H->eotd_acc = 0;
+	  H->eotd_gathering = 0;
+	  H->olen = 0;
+	  H->frame_len = 0;
+	}
 	return;
 } // end eotd_rec_bit
 

src/multi_modem.c

@@ -103,6 +103,7 @@
 #include "fx25.h"
 #include "version.h"
 #include "ais.h"
+#include "eotd.h"
 
 
 
@@ -342,6 +343,13 @@ void multi_modem_process_rec_frame (int chan, int subchan, int slice, unsigned c
 
 	  // alevel gets in there somehow making me question why it is passed thru here.
 	}
+	else if (save_audio_config_p->achan[chan].modem_type == MODEM_EOTD) {
+	  char nmea[300];
+          eotd_to_nmea (fbuf, flen, nmea, sizeof(nmea));
+	  char monfmt[276];
+	  snprintf (monfmt, sizeof(monfmt), "EOTD>%s%1d%1d:{%c%c%s", APP_TOCALL, MAJOR_VERSION, MINOR_VERSION, USER_DEF_USER_ID, USER_DEF_TYPE_AIS, nmea);
+	  pp = ax25_from_text (monfmt, 1);
+	}
 	else {
 	  pp = ax25_from_frame (fbuf, flen, alevel);
 	}