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VK1ET : Fix AC12 Altitude decoding

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This commit is contained in:
Malcolm Robb 2013-05-08 19:34:47 +01:00
parent 71ace95fd4
commit fb5ef77cd1
1 changed files with 8 additions and 7 deletions
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15
dump1090.c
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@ -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 "1.04.0705.13"
#define MODES_DUMP1090_VERSION "1.04.0805.13"
#define MODES_DEFAULT_RATE 2000000
#define MODES_DEFAULT_FREQ 1090000000
@ -1213,9 +1213,9 @@ int decodeID13Field(int ID13Field) {
if (ID13Field & 0x0200) {hexGillham |= 0x2000;} // Bit 9 = A2
if (ID13Field & 0x0100) {hexGillham |= 0x0040;} // Bit 8 = C4
if (ID13Field & 0x0080) {hexGillham |= 0x4000;} // Bit 7 = A4
//if (ID13Field & 0x0040) {hexGillham |= 0x0800;} // Bit 6 = X or Q
//if (ID13Field & 0x0040) {hexGillham |= 0x0800;} // Bit 6 = X or M
if (ID13Field & 0x0020) {hexGillham |= 0x0100;} // Bit 5 = B1
if (ID13Field & 0x0010) {hexGillham |= 0x0001;} // Bit 4 = D1
if (ID13Field & 0x0010) {hexGillham |= 0x0001;} // Bit 4 = D1 or Q
if (ID13Field & 0x0008) {hexGillham |= 0x0200;} // Bit 3 = B2
if (ID13Field & 0x0004) {hexGillham |= 0x0002;} // Bit 2 = D2
if (ID13Field & 0x0002) {hexGillham |= 0x0400;} // Bit 1 = B4
@ -1259,18 +1259,19 @@ int decodeAC13Field(int AC13Field, int *unit) {
//
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
/// N is the 11 bit integer resulting from the removal of bit Q at bit 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 = n = ModeAToModeC(decodeID13Field(AC12Field));
// Make N a 13 bit Gillham coded altitude by inserting M=0 at bit 6
int n = ((AC12Field & 0x0FC0) << 1) |
(AC12Field & 0x003F);
n = ModeAToModeC(decodeID13Field(n));
if (n < -12) {n = 0;}
return (100 * n);