AFG/dump1090
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Squawk extraction fixed.

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This commit is contained in:
antirez 2013-01-19 16:10:30 +01:00
parent b4805ea7d4
commit c9bb48675c
1 changed files with 34 additions and 3 deletions
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37
dump1090.c
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@ -705,7 +705,7 @@ int ICAOAddressWasRecentlySeen(uint32_t addr) {
* If the function successfully recovers a message with a correct checksum * If the function successfully recovers a message with a correct checksum
* it returns 1. Otherwise 0 is returned. */ * it returns 1. Otherwise 0 is returned. */
int bruteForceAP(unsigned char *msg, int msgbits) { int bruteForceAP(unsigned char *msg, int msgbits) {
unsigned char aux[MODES_LONG_MSG_BITS/8]; unsigned char aux[MODES_LONG_MSG_BYTES];
int msgtype = msg[0]>>3; int msgtype = msg[0]>>3;
if (msgtype == 0 || /* Short air surveillance */ if (msgtype == 0 || /* Short air surveillance */
@ -907,7 +907,37 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
mm->dr = msg[1] >> 3 & 31; /* Request extraction of downlink request. */ mm->dr = msg[1] >> 3 & 31; /* Request extraction of downlink request. */
mm->um = ((msg[1] & 7)<<3)| /* Request extraction of downlink request. */ mm->um = ((msg[1] & 7)<<3)| /* Request extraction of downlink request. */
msg[2]>>5; msg[2]>>5;
mm->identity = (msg[2]&31 << 8) | msg[3]; /* 13 bits identity. */
/* In the squawk (identity) field bits are interleaved like that
* (message bit 20 to bit 32):
*
* C1-A1-C2-A2-C4-A4-ZERO-B1-D1-B2-D2-B4-D4
*
* So every group of three bits A, B, C, D represent an integer
* from 0 to 7.
*
* The actual meaning is just 4 octal numbers, but we convert it
* into a base ten number tha happens to represent the four
* octal numbers.
*
* For more info: http://en.wikipedia.org/wiki/Gillham_code */
{
int a,b,c,d;
a = ((msg[3] & 0x80) >> 5) |
((msg[2] & 0x02) >> 0) |
((msg[2] & 0x08) >> 3);
b = ((msg[3] & 0x02) << 1) |
((msg[3] & 0x08) >> 2) |
((msg[3] & 0x20) >> 5);
c = ((msg[2] & 0x01) << 2) |
((msg[2] & 0x04) >> 1) |
((msg[2] & 0x10) >> 4);
d = ((msg[3] & 0x01) << 2) |
((msg[3] & 0x04) >> 1) |
((msg[3] & 0x10) >> 4);
mm->identity = a*1000 + b*100 + c*10 + d;
}
/* Check if we can check the checksum for the Downlink Formats where /* Check if we can check the checksum for the Downlink Formats where
* the checksum is xored with the aircraft ICAO address. We try to * the checksum is xored with the aircraft ICAO address. We try to
@ -926,6 +956,7 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
mm->crcok = 0; mm->crcok = 0;
} }
} }
/* If this is DF 11 or DF 17 and the checksum was ok, /* If this is DF 11 or DF 17 and the checksum was ok,
* we can add this address to the list of recently seen * we can add this address to the list of recently seen
* addresses. */ * addresses. */
@ -1056,7 +1087,7 @@ void displayModesMessage(struct modesMessage *mm) {
printf(" Flight Status : %s\n", fs_str[mm->fs]); printf(" Flight Status : %s\n", fs_str[mm->fs]);
printf(" DR : %d\n", mm->dr); printf(" DR : %d\n", mm->dr);
printf(" UM : %d\n", mm->um); printf(" UM : %d\n", mm->um);
printf(" Squawk : %o (octal)\n", mm->identity); printf(" Squawk : %d\n", mm->identity);
printf(" ICAO Address : %02x%02x%02x\n", mm->aa1, mm->aa2, mm->aa3); printf(" ICAO Address : %02x%02x%02x\n", mm->aa1, mm->aa2, mm->aa3);
if (mm->msgtype == 21) { if (mm->msgtype == 21) {