Backport Flightgear server from private tx branch, collapse commits.

* Added Flightgear multiplayer output interface to uhd_modes.py. This allows flight with live traffic in fgfs.
* Quaternion library borrowed from PyPi and modified to generate angle/axis representation and construct rotation quat from lat/lon to ECEF.
* Miscellaneous enhancements and cleanup to fix timestamps, add aircraft type field (seems to be unused anyway), turnrate info

lib/CMakeLists.txt

@@ -25,7 +25,7 @@ include(GrPlatform) #define LIB_SUFFIX
 add_library(air_modes SHARED
     air_modes_preamble.cc
     air_modes_slicer.cc
-    modes_parity.cc
+    modes_crc.cc
 )
 target_link_libraries(air_modes ${Boost_LIBRARIES} ${GRUEL_LIBRARIES} ${GNURADIO_CORE_LIBRARIES})
 set_target_properties(air_modes PROPERTIES DEFINE_SYMBOL "AIR_MODES_EXPORTS")

lib/air_modes_preamble.cc

@@ -84,13 +84,15 @@ static double tag_to_timestamp(gr_tag_t tstamp, uint64_t abs_sample_cnt, double
 	uint64_t ts_sample, last_whole_stamp;
 	double last_frac_stamp;
 
-	if(tstamp.key == NULL || pmt::pmt_symbol_to_string(tstamp.key) != "timestamp") return 0;
+	if(tstamp.key == NULL || pmt::pmt_symbol_to_string(tstamp.key) != "rx_time") return 0;
 
 	last_whole_stamp = pmt::pmt_to_uint64(pmt::pmt_tuple_ref(tstamp.value, 0));
 	last_frac_stamp = pmt::pmt_to_double(pmt::pmt_tuple_ref(tstamp.value, 1));
 	ts_sample = tstamp.offset;
-	//std::cout << "HEY WE GOT A STAMP AT " << ticks << " TICKS AT SAMPLE " << ts_sample << " ABS SAMPLE CNT IS " << abs_sample_cnt << std::endl;
-	return double(abs_sample_cnt * secs_per_sample) + last_whole_stamp + last_frac_stamp;
+	
+	double tstime = double(abs_sample_cnt * secs_per_sample) + last_whole_stamp + last_frac_stamp;
+	//std::cout << "HEY WE GOT A STAMP AT " << tstime << " TICKS AT SAMPLE " << ts_sample << " ABS SAMPLE CNT IS " << abs_sample_cnt << std::endl;
+	return tstime;
 }
 
 int air_modes_preamble::general_work(int noutput_items,
@@ -112,7 +114,7 @@ int air_modes_preamble::general_work(int noutput_items,
 
 	uint64_t abs_sample_cnt = nitems_read(0);
 	std::vector<gr_tag_t> tstamp_tags;
-	get_tags_in_range(tstamp_tags, 0, abs_sample_cnt, abs_sample_cnt + ninputs, pmt::pmt_string_to_symbol("timestamp"));
+	get_tags_in_range(tstamp_tags, 0, abs_sample_cnt, abs_sample_cnt + ninputs, pmt::pmt_string_to_symbol("rx_time"));
 	//tags.back() is the most recent timestamp, then.
 	if(tstamp_tags.size() > 0) {
 		d_timestamp = tstamp_tags.back();
@@ -174,11 +176,7 @@ int air_modes_preamble::general_work(int noutput_items,
 			}
 
 			//get the timestamp of the preamble
-			double tstamp = 0;
-
-			if(d_timestamp.offset != 0) {
-				tstamp = tag_to_timestamp(d_timestamp, abs_sample_cnt + i, d_secs_per_sample);
-			}
+			double tstamp = tag_to_timestamp(d_timestamp, abs_sample_cnt + i, d_secs_per_sample);
 
 			//now tag the preamble
 			add_item_tag(0, //stream ID

lib/air_modes_slicer.cc

@@ -29,7 +29,7 @@
 #include <air_modes_types.h>
 #include <sstream>
 #include <iomanip>
-#include <modes_parity.h>
+#include <modes_crc.h>
 #include <iostream>
 #include <gr_tags.h>
 #include <air_modes_api.h>
@@ -172,18 +172,18 @@ int air_modes_slicer::work(int noutput_items,
 		if(rx_packet.type == Short_Packet && rx_packet.message_type != 11 && rx_packet.numlowconf > 0) {continue;}
 		if(rx_packet.message_type == 11 && rx_packet.numlowconf >= 10) {continue;}
 			
-		rx_packet.parity = modes_check_parity(rx_packet.data, packet_length);
+		rx_packet.crc = modes_check_crc(rx_packet.data, packet_length);
 
-		//parity for packets that aren't type 11 or type 17 is encoded with the transponder ID, which we don't know
+		//crc for packets that aren't type 11 or type 17 is encoded with the transponder ID, which we don't know
 		//therefore we toss 'em if there's syndrome
-		//parity for the other short packets is usually nonzero, so they can't really be trusted that far
-		if(rx_packet.parity && (rx_packet.message_type == 11 || rx_packet.message_type == 17)) {continue;}
+		//crc for the other short packets is usually nonzero, so they can't really be trusted that far
+		if(rx_packet.crc && (rx_packet.message_type == 11 || rx_packet.message_type == 17)) {continue;}
 
 		//we no longer attempt to brute force error correct via syndrome. it really only gets you 1% additional returns,
 		//at the expense of a lot of CPU time and complexity
 
 		//we'll replicate some data by sending the message type as the first field, followed by the first 8+24=32 bits of the packet, followed by
-		//56 long packet data bits if applicable (zero-padded if not), followed by parity
+		//56 long packet data bits if applicable (zero-padded if not), followed by crc
 
 		d_payload.str("");
 		d_payload << std::dec << std::setw(2) << std::setfill('0') << rx_packet.message_type << std::hex << " ";
@@ -209,7 +209,7 @@ int air_modes_slicer::work(int noutput_items,
 			}
 		}
 			
-		d_payload << " " << std::setw(6) << rx_packet.parity << " " << std::dec << rx_packet.reference_level
+		d_payload << " " << std::setw(6) << rx_packet.crc << " " << std::dec << rx_packet.reference_level
 		          << " " << std::setprecision(10) << std::setw(10) << rx_packet.timestamp;
 			gr_message_sptr msg = gr_make_message_from_string(std::string(d_payload.str()));
 		d_queue->handle(msg);

lib/modes_crc.cc

@@ -27,7 +27,7 @@
 
 #include <stdio.h>
 #include <air_modes_types.h>
-#include <modes_parity.h>
+#include <modes_crc.h>
 #include <math.h>
 #include <stdlib.h>
 
@@ -35,7 +35,7 @@
  *   Index is bit position with bit 0 being the first bit after preamble
  *   On short frames an offset of 56 is used.
 */
-const unsigned int modes_parity_table[112] =
+const unsigned int modes_crc_table[112] =
 {
     0x3935ea,  // Start of Long Frame CRC
     0x1c9af5,
@@ -150,29 +150,16 @@ const unsigned int modes_parity_table[112] =
     0x000002,
     0x000001,
 };
-int modes_check_parity(unsigned char data[], int length)
+
+int modes_check_crc(unsigned char data[], int length)
 {
-	int short_crc, long_crc, i;
-	// Check both long and short
-	short_crc = 0;
-	long_crc = 0;
-	for(i = 0; i < 56; i++)
+	int crc, i;
+	for(i = 0; i < length; i++)
 	{
 		if(data[i/8] & (1 << (7-(i%8))))
 		{
-			short_crc ^= modes_parity_table[i+56];
-			long_crc ^= modes_parity_table[i];
-
+			crc ^= modes_crc_table[i+(112-length)];
 		}
 	}
-	for( ; i < length; i++)
-	{
-		if(data[i/8] & (1 << (7-(i%8))))
-		{
-			long_crc ^= modes_parity_table[i];
-		}
-	}
-	if(length == 112) return long_crc;
-	else return short_crc;
+    return crc;
 }
-