[hamradio-commits] [dump1090] 119/373: Mode S Gillham altitude changes
Matthew Ernisse
mernisse-guest at moszumanska.debian.org
Thu Oct 23 14:58:11 UTC 2014
This is an automated email from the git hooks/post-receive script.
mernisse-guest pushed a commit to branch backport
in repository dump1090.
commit 19c11509e79b106cb4dbb8fe54186ce84881a4fb
Author: Malcolm Robb <Support at ATTAvionics.com>
Date: Mon Apr 29 18:33:59 2013 +0100
Mode S Gillham altitude changes
Modify all the Mode=S Gillham altitude decoding to use a new function
decodeGillhamField()
Change the Mode-S signal strength so that it rounds to the nearest
integer
---
dump1090.c | 139 ++++++++++++++++++++++++-------------------------------------
1 file changed, 55 insertions(+), 84 deletions(-)
diff --git a/dump1090.c b/dump1090.c
index c0c966d..92a9a68 100644
--- a/dump1090.c
+++ b/dump1090.c
@@ -56,7 +56,7 @@
// MinorVer changes when additional features are added, but not for bug fixes (range 00-99)
// DayDate & Year changes for all changes, including for bug fixes. It represent the release date of the update
//
-#define MODES_DUMP1090_VERSION "1.04.2804.13"
+#define MODES_DUMP1090_VERSION "1.04.2904.13"
#define MODES_DEFAULT_RATE 2000000
#define MODES_DEFAULT_FREQ 1090000000
@@ -1316,41 +1316,58 @@ int bruteForceAP(unsigned char *msg, struct modesMessage *mm) {
return (0);
}
//
+// In the squawk (identity) field bits are interleaved as follows in
+// (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 hex
+// number tha happens to represent the four octal numbers.
+//
+// For more info: http://en.wikipedia.org/wiki/Gillham_code
+//
+int decodeGillhamField(int rawGillham) {
+ int hexGillham = 0;
+
+ if (rawGillham & 0x1000) {hexGillham |= 0x0010;} // Bit 12 = C1
+ if (rawGillham & 0x0800) {hexGillham |= 0x1000;} // Bit 11 = A1
+ if (rawGillham & 0x0400) {hexGillham |= 0x0020;} // Bit 10 = C2
+ if (rawGillham & 0x0200) {hexGillham |= 0x2000;} // Bit 9 = A2
+ if (rawGillham & 0x0100) {hexGillham |= 0x0040;} // Bit 8 = C4
+ if (rawGillham & 0x0080) {hexGillham |= 0x4000;} // Bit 7 = A4
+ //if (rawGillham & 0x0040) {hexGillham |= 0x0800;} // Bit 6 = X or Q
+ if (rawGillham & 0x0020) {hexGillham |= 0x0100;} // Bit 5 = B1
+ if (rawGillham & 0x0010) {hexGillham |= 0x0001;} // Bit 4 = D1
+ if (rawGillham & 0x0008) {hexGillham |= 0x0200;} // Bit 3 = B2
+ if (rawGillham & 0x0004) {hexGillham |= 0x0002;} // Bit 2 = D2
+ if (rawGillham & 0x0002) {hexGillham |= 0x0400;} // Bit 1 = B4
+ if (rawGillham & 0x0001) {hexGillham |= 0x0004;} // Bit 0 = D4
+
+ return (hexGillham);
+ }
+//
// Decode the 13 bit AC altitude field (in DF 20 and others).
// Returns the altitude, and set 'unit' to either MODES_UNIT_METERS or MDOES_UNIT_FEETS.
//
-int decodeAC13Field(unsigned char *msg, int *unit) {
- int msg2 = msg[2];
- int msg3 = msg[3];
- int m_bit = msg3 & 0x40; // set = meters, clear = feet
- int q_bit = msg3 & 0x10; // set = 25 ft encoding, clear = Gillham Mode C encoding
+int decodeAC13Field(int AC13Field, int *unit) {
+ int m_bit = AC13Field & 0x0040; // set = meters, clear = feet
+ int q_bit = AC13Field & 0x0010; // set = 25 ft encoding, clear = Gillham Mode C encoding
+ AC13Field &= 0x1FFF; // limit the field to 13 bits
if (!m_bit) {
*unit = MODES_UNIT_FEET;
if (q_bit) {
// N is the 11 bit integer resulting from the removal of bit Q and M
- int n = ((msg2 & 0x1F) << 6) |
- ((msg3 & 0x80) >> 2) |
- ((msg3 & 0x20) >> 1) |
- (msg3 & 0x0F);
+ int n = ((AC13Field & 0x1F80) >> 2) |
+ ((AC13Field & 0x0020) >> 1) |
+ (AC13Field & 0x000F);
// The final altitude is resulting number multiplied by 25, minus 1000.
return ((n * 25) - 1000);
} else {
// N is an 11 bit Gillham coded altitude
- int n = 0;
- if (msg2 & 0x10) {n |= 0x0010;} // Bit 20 = C1;
- if (msg2 & 0x08) {n |= 0x1000;} // Bit 21 = A1;
- if (msg2 & 0x04) {n |= 0x0020;} // Bit 22 = C2;
- if (msg2 & 0x02) {n |= 0x2000;} // Bit 23 = A2;
- if (msg2 & 0x01) {n |= 0x0040;} // Bit 24 = C4;
- if (msg3 & 0x80) {n |= 0x4000;} // Bit 25 = A4;
- if (msg3 & 0x20) {n |= 0x0100;} // Bit 27 = B1;
- if (msg3 & 0x08) {n |= 0x0200;} // Bit 29 = B2;
- if (msg3 & 0x04) {n |= 0x0002;} // Bit 30 = D2;
- if (msg3 & 0x02) {n |= 0x0400;} // Bit 31 = B4;
- if (msg3 & 0x01) {n |= 0x0004;} // Bit 32 = D4;
-
- n = ModeAToModeC(n);
+ int n = ModeAToModeC(decodeGillhamField(AC13Field));
if (n < -12) {n = 0;}
return (100 * n);
@@ -1364,33 +1381,20 @@ int decodeAC13Field(unsigned char *msg, int *unit) {
//
// Decode the 12 bit AC altitude field (in DF 17 and others).
//
-int decodeAC12Field(unsigned char *msg, int *unit) {
- int msg5 = msg[5];
- int msg6 = msg[6];
- int q_bit = msg5 & 1; // Bit 48 = Q
+int decodeAC12Field(int AC12Field, int *unit) {
+ int q_bit = AC12Field & 0x10; // Bit 48 = Q
+ AC12Field &= 0x0FFF; // limit the field to 12 bits
*unit = MODES_UNIT_FEET;
if (q_bit) {
/// N is the 11 bit integer resulting from the removal of bit Q
- int n = ((msg5 & 0xFE) << 3) | ((msg6 & 0xF0) >> 4);
+ int n = ((AC12Field & 0x0FE0) >> 1) |
+ (AC12Field & 0x000F);
// The final altitude is the resulting number multiplied by 25, minus 1000.
return ((n * 25) - 1000);
} else {
// N is an 11 bit Gillham coded altitude
- int n = 0;
- if (msg5 & 0x80) {n |= 0x0010;} // Bit 41 = C1;
- if (msg5 & 0x40) {n |= 0x1000;} // Bit 42 = A1;
- if (msg5 & 0x20) {n |= 0x0020;} // Bit 43 = C2;
- if (msg5 & 0x10) {n |= 0x2000;} // Bit 44 = A2;
- if (msg5 & 0x08) {n |= 0x0040;} // Bit 45 = C4;
- if (msg5 & 0x04) {n |= 0x4000;} // Bit 46 = A4;
- if (msg5 & 0x02) {n |= 0x0100;} // Bit 47 = B1;
- if (msg6 & 0x80) {n |= 0x0200;} // Bit 49 = B2;
- if (msg6 & 0x40) {n |= 0x0002;} // Bit 50 = D2;
- if (msg6 & 0x20) {n |= 0x0400;} // Bit 51 = B4;
- if (msg6 & 0x10) {n |= 0x0004;} // Bit 52 = D4;
-
- n = ModeAToModeC(n);
+ int n = n = ModeAToModeC(decodeGillhamField(AC12Field));
if (n < -12) {n = 0;}
return (100 * n);
@@ -1515,41 +1519,7 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
mm->um = ((msg[1] & 7)<<3)| /* Request extraction of downlink request. */
msg[2]>>5;
- /* 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 hex number tha happens to represent the four
- * octal numbers.
- *
- * For more info: http://en.wikipedia.org/wiki/Gillham_code */
- {
- int hexSquawk = 0;
- unsigned char rawSquawk;
-
- rawSquawk = msg[2];
- if (rawSquawk & 0x01) {hexSquawk |= 0x0040;} // C4
- if (rawSquawk & 0x02) {hexSquawk |= 0x2000;} // A2
- if (rawSquawk & 0x04) {hexSquawk |= 0x0020;} // C2
- if (rawSquawk & 0x08) {hexSquawk |= 0x1000;} // A1
- if (rawSquawk & 0x10) {hexSquawk |= 0x0010;} // C1
-
- rawSquawk = msg[3];
- if (rawSquawk & 0x01) {hexSquawk |= 0x0004;} // D4
- if (rawSquawk & 0x02) {hexSquawk |= 0x0400;} // B4
- if (rawSquawk & 0x04) {hexSquawk |= 0x0002;} // D2
- if (rawSquawk & 0x08) {hexSquawk |= 0x0200;} // B2
- if (rawSquawk & 0x10) {hexSquawk |= 0x0001;} // D1
- if (rawSquawk & 0x20) {hexSquawk |= 0x0100;} // B1
- if (rawSquawk & 0x80) {hexSquawk |= 0x4000;} // A4
-
- mm->modeA = hexSquawk;
- }
+ mm->modeA = decodeGillhamField((msg[2] << 8) | msg[3]);
/* DF 11 & 17: try to populate our ICAO addresses whitelist.
* DFs with an AP field (xored addr and crc), try to decode it. */
@@ -1572,10 +1542,10 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
}
}
- /* Decode 13 bit altitude for DF0, DF4, DF16, DF20 */
- if (mm->msgtype == 0 || mm->msgtype == 4 ||
+ // Fields for DF0, DF4, DF16, DF20 13 bit altitude
+ if (mm->msgtype == 0 || mm->msgtype == 4 ||
mm->msgtype == 16 || mm->msgtype == 20) {
- mm->altitude = decodeAC13Field(msg, &mm->unit);
+ mm->altitude = decodeAC13Field(((msg[2] << 8) | msg[3]), &mm->unit);
}
/* Decode extended squitter specific stuff. */
@@ -1598,7 +1568,7 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
/* Airborne position Message */
mm->fflag = msg[6] & (1<<2);
mm->tflag = msg[6] & (1<<3);
- mm->altitude = decodeAC12Field(msg,&mm->unit);
+ mm->altitude = decodeAC12Field(((msg[5] << 4) | (msg[6] >> 4)), &mm->unit);
mm->raw_latitude = ((msg[6] & 3) << 15) |
(msg[7] << 7) |
(msg[8] >> 1);
@@ -2083,8 +2053,9 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
}
}
- // Don't forget to add 4 for the preamble samples. This also removes any risk of dividing by zero.
- sigStrength /= 60;
+ // We measured signal strength over the first 56 bits. Don't forget to add 4
+ // for the preamble samples, so round up and divide by 60.
+ sigStrength = (sigStrength + 29) / 60;
/* If we reached this point, and error is zero, we are very likely
* with a Mode S message in our hands, but it may still be broken
--
Alioth's /usr/local/bin/git-commit-notice on /srv/git.debian.org/git/pkg-hamradio/dump1090.git
More information about the pkg-hamradio-commits
mailing list