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Overhaul mode A/C matching to be much cheaper.

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The old matching process which tracked mode A values as pseudo-aircraft
got very, very expensive with a large number of mode A/C messages (and
with lots of single-bit errors, which seems common with a Beast doing
the reception)

Instead just count A/C messages directly into a 4096-entry array (which
is very fast) and periodically scan the mode S aircraft list to see if
we can match anything up (which is fixed overhead + cost proportional
to the number of mode S aircraft)
This commit is contained in:
Oliver Jowett 2016-10-11 18:00:11 +01:00
parent 60f1f3bcb6
commit 25ea6d398b
6 changed files with 111 additions and 140 deletions
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18
track.h
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@ -59,6 +59,11 @@
/* Maximum validity of an aircraft position */
#define TRACK_AIRCRAFT_POSITION_TTL 60000
/* Minimum number of repeated Mode A/C replies with a particular Mode A code needed in a
* 1 second period before accepting that code.
*/
#define TRACK_MODEAC_MIN_MESSAGES 3
typedef struct {
datasource_t source; /* where the data came from */
uint64_t updated; /* when it arrived */
@ -82,7 +87,6 @@ struct aircraft {
data_validity altitude_valid;
int altitude; // Altitude (Baro)
unsigned altitude_modeC; // (as a Mode C value)
data_validity altitude_gnss_valid;
int altitude_gnss; // Altitude (GNSS)
@ -134,9 +138,8 @@ struct aircraft {
double lat, lon; // Coordinated obtained from CPR encoded data
unsigned pos_nuc; // NUCp of last computed position
long modeAcount; // Mode A Squawk hit Count
long modeCcount; // Mode C Altitude hit Count
int modeACflags; // Flags for mode A/C recognition
int modeA_hit; // did our squawk match a possible mode A reply in the last check period?
int modeC_hit; // did our altitude match a possible mode C reply in the last check period?
int fatsv_emitted_altitude; // last FA emitted altitude
int fatsv_emitted_altitude_gnss; // -"- GNSS altitude
@ -159,6 +162,13 @@ struct aircraft {
struct modesMessage first_message; // A copy of the first message we received for this aircraft.
};
/* Mode A/C tracking is done separately, not via the aircraft list,
* and via a flat array rather than a list since there are only 4k possible values
* (nb: we ignore the ident/SPI bit when tracking)
*/
extern uint32_t modeAC_count[4096];
extern uint32_t modeAC_match[4096];
/* is this bit of data valid? */
static inline int trackDataValid(const data_validity *v)
{