AFG/dump1090
3
0
Fork 0
Code Issues Pull requests Packages Projects Releases Wiki Activity

Create a preamble pointer in the message detector loop

Browse source 
Create a preamble pointer in the message detector loop

Create a pointer, pPreamble, which points to the start of the preamble
in the analogue sample buffer m[]. So pPreamble = &m[p] Then use this
pointer to perform the preamble detection tests.  It should save a few
cpu cycles per test because accessing pPointer[2] should be quicker than
m[p+2].

Also move the decision on whether to try OutOfPhase correction to the
end of the first pass, rather than automatically going into phase
correction if the first pass fails. This saves two memcpy's if the
decision in the second pass is to not do phase correction.
This commit is contained in:
Malcolm Robb 2013-04-10 01:12:50 +01:00
parent 316b456835 70031e1234
commit 09af545933
1 changed files with 35 additions and 41 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

74
dump1090.c
View file

@ -1258,13 +1258,13 @@ void computeMagnitudeVector(void) {
* Return 1 if the message is out of fase right-size
* Return 0 if the message is not particularly out of phase.
*
* Note: this function will access m[-1], so the caller should make sure to
* Note: this function will access pPreamble[-1], so the caller should make sure to
* call it only if we are not at the start of the current buffer. */
int detectOutOfPhase(uint16_t *m) {
if (m[3] > m[2]/3) return 1;
if (m[10] > m[9]/3) return 1;
if (m[6] > m[7]/3) return -1;
if (m[-1] > m[1]/3) return -1;
int detectOutOfPhase(uint16_t *pPreamble) {
if (pPreamble[ 3] > pPreamble[2]/3) return 1;
if (pPreamble[10] > pPreamble[9]/3) return 1;
if (pPreamble[ 6] > pPreamble[7]/3) return -1;
if (pPreamble[-1] > pPreamble[1]/3) return -1;
return 0;
}
@ -1298,8 +1298,6 @@ int detectOutOfPhase(uint16_t *m) {
* correct way. */
void applyPhaseCorrection(uint16_t *m) {
int j;
m += MODES_PREAMBLE_SAMPLES; /* Skip preamble. */
for (j = 0; j < MODES_LONG_MSG_SAMPLES; j += 2) {
if (m[j] > m[j+1]) {
/* One */
@ -1347,28 +1345,29 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
for (j = 0; j < mlen; j++) {
int low, high, delta, i, errors;
int good_message = 0;
uint16_t *pPreamble;
int msglen;
pPreamble = &m[j];
if (use_correction) goto good_preamble; /* We already checked it. */
/* First check of relations between the first 10 samples
* representing a valid preamble. We don't even investigate further
* if this simple test is not passed. */
if (!(m[j] > m[j+1] &&
m[j+1] < m[j+2] &&
m[j+2] > m[j+3] &&
m[j+3] < m[j] &&
m[j+4] < m[j] &&
m[j+5] < m[j] &&
m[j+6] < m[j] &&
m[j+7] > m[j+8] &&
m[j+8] < m[j+9] &&
m[j+9] > m[j+6]))
if (!(pPreamble[0] > pPreamble[1] &&
pPreamble[1] < pPreamble[2] &&
pPreamble[2] > pPreamble[3] &&
pPreamble[3] < pPreamble[0] &&
pPreamble[4] < pPreamble[0] &&
pPreamble[5] < pPreamble[0] &&
pPreamble[6] < pPreamble[0] &&
pPreamble[7] > pPreamble[8] &&
pPreamble[8] < pPreamble[9] &&
pPreamble[9] > pPreamble[6]))
{
if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Unexpected ratio among first 10 samples",
msg, m, j);
*pPreamble > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Unexpected ratio among first 10 samples", msg, m, j);
continue;
}
@ -1376,31 +1375,27 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
* of the high spikes level. We don't test bits too near to
* the high levels as signals can be out of phase so part of the
* energy can be in the near samples. */
high = (m[j]+m[j+2]+m[j+7]+m[j+9])/6;
if (m[j+4] >= high ||
m[j+5] >= high)
high = (pPreamble[0]+pPreamble[2]+pPreamble[7]+pPreamble[9])/6;
if (pPreamble[4] >= high ||
pPreamble[5] >= high)
{
if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage(
"Too high level in samples between 3 and 6",
msg, m, j);
*pPreamble > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Too high level in samples between 3 and 6", msg, m, j);
continue;
}
/* Similarly samples in the range 11-14 must be low, as it is the
* space between the preamble and real data. Again we don't test
* bits too near to high levels, see above. */
if (m[j+11] >= high ||
m[j+12] >= high ||
m[j+13] >= high ||
m[j+14] >= high)
if (pPreamble[11] >= high ||
pPreamble[12] >= high ||
pPreamble[13] >= high ||
pPreamble[14] >= high)
{
if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
m[j] > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage(
"Too high level in samples between 10 and 15",
msg, m, j);
*pPreamble > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Too high level in samples between 10 and 15", msg, m, j);
continue;
}
Modes.stat_valid_preamble++;
@ -1410,10 +1405,9 @@ good_preamble:
* magnitude correction. */
if (use_correction) {
memcpy(aux,m+j+MODES_PREAMBLE_SAMPLES,sizeof(aux));
if (j && detectOutOfPhase(m+j)) {
applyPhaseCorrection(m+j);
applyPhaseCorrection(m+j+MODES_PREAMBLE_SAMPLES);
Modes.stat_out_of_phase++;
}
/* TODO ... apply other kind of corrections. */
}
@ -1537,7 +1531,7 @@ good_preamble:
}
/* Retry with phase correction if possible. */
if (!good_message && !use_correction) {
if (!good_message && !use_correction && j && detectOutOfPhase(pPreamble)) {
j--;
use_correction = 1;
} else {