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BUGFIX : Missed data causes timestamp slip

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The Mutex on the RTL data reader thread does not "force" the data
processing thread to execute. Therefore, if the processor is busy, it is
possible for a second RTL callback to occur before the data from the
first has been processed. This will cause the loss of the first data,
but worse, it will cause a slip in the timestamp. This upsets Beamfinder
and MLAT operation in PlanePlotter.

To solve this, keep a Fifo buffer which is filled by the callback
thread, and emptied by the data processing thread. The fifo is the same
size as the number of buffers requested in the call to
rtlsdr_read_async().

Note - we only put the value of the pointer supplied in the callback
into the fifo. We do not attempt to cache the data in the buffer pointed
to by the pointer.  This would require us to memcopy() 2Mbytes per
second, which we don't want to do if we don't have to because it will
only make the processor loading worse. Instead, we assume that the data
in the buffer will remain valid after the callback returns, at least
until it is overwritten by new data.

It is still possible for us to lose data if we can't process it quickly
enough. However, we can now detect this loss of data when the fifo is
almost full, and correct the timestamp for the lost block/blocks.
This commit is contained in:
Malcolm Robb 2014-02-22 23:11:13 +00:00
parent 24080a22b1
commit 75a4c6ee21
4 changed files with 108 additions and 48 deletions

135
dump1090.c
View file

@ -92,7 +92,7 @@ void modesInit(void) {
// Allocate the various buffers used by Modes
if ( ((Modes.icao_cache = (uint32_t *) malloc(sizeof(uint32_t) * MODES_ICAO_CACHE_LEN * 2) ) == NULL) ||
((Modes.data = (uint16_t *) malloc(MODES_ASYNC_BUF_SIZE) ) == NULL) ||
((Modes.pFileData = (uint16_t *) malloc(MODES_ASYNC_BUF_SIZE) ) == NULL) ||
((Modes.magnitude = (uint16_t *) malloc(MODES_ASYNC_BUF_SIZE+MODES_PREAMBLE_SIZE+MODES_LONG_MSG_SIZE) ) == NULL) ||
((Modes.maglut = (uint16_t *) malloc(sizeof(uint16_t) * 256 * 256) ) == NULL) ||
((Modes.beastOut = (char *) malloc(MODES_RAWOUT_BUF_SIZE) ) == NULL) ||
@ -104,7 +104,7 @@ void modesInit(void) {
// Clear the buffers that have just been allocated, just in-case
memset(Modes.icao_cache, 0, sizeof(uint32_t) * MODES_ICAO_CACHE_LEN * 2);
memset(Modes.data, 127, MODES_ASYNC_BUF_SIZE);
memset(Modes.pFileData,127, MODES_ASYNC_BUF_SIZE);
memset(Modes.magnitude, 0, MODES_ASYNC_BUF_SIZE+MODES_PREAMBLE_SIZE+MODES_LONG_MSG_SIZE);
// Validate the users Lat/Lon home location inputs
@ -133,8 +133,9 @@ void modesInit(void) {
{Modes.net_output_raw_rate = MODES_RAWOUT_BUF_RATE;}
// Initialise the Block Timers to something half sensible
ftime(&Modes.stSystemTimeRTL);
Modes.stSystemTimeBlk = Modes.stSystemTimeRTL;
ftime(&Modes.stSystemTimeBlk);
for (i = 0; i < MODES_ASYNC_BUF_NUMBER; i++)
{Modes.stSystemTimeRTL[i] = Modes.stSystemTimeBlk;}
// Each I and Q value varies from 0 to 255, which represents a range from -1 to +1. To get from the
// unsigned (0-255) range you therefore subtract 127 (or 128 or 127.5) from each I and Q, giving you
@ -250,13 +251,35 @@ void rtlsdrCallback(unsigned char *buf, uint32_t len, void *ctx) {
MODES_NOTUSED(ctx);
// Lock the data buffer variables before accessing them
pthread_mutex_lock(&Modes.data_mutex);
ftime(&Modes.stSystemTimeRTL);
if (len > MODES_ASYNC_BUF_SIZE) len = MODES_ASYNC_BUF_SIZE;
// Read the new data
memcpy(Modes.data, buf, len);
Modes.data_ready = 1;
// Signal to the other thread that new data is ready
rtlsdrStats(buf);
Modes.iDataIn &= (MODES_ASYNC_BUF_NUMBER-1); // Just incase!!!
// Get the system time for this block
ftime(&Modes.stSystemTimeRTL[Modes.iDataIn]);
if (len > MODES_ASYNC_BUF_SIZE) {len = MODES_ASYNC_BUF_SIZE;}
// Queue the new data
Modes.pData[Modes.iDataIn] = (uint16_t *) buf;
Modes.iDataIn = (MODES_ASYNC_BUF_NUMBER-1) & (Modes.iDataIn + 1);
Modes.iDataReady = (MODES_ASYNC_BUF_NUMBER-1) & (Modes.iDataIn - Modes.iDataOut);
if (Modes.iDataReady == 0) {
// Ooooops. We've just received the MODES_ASYNC_BUF_NUMBER'th outstanding buffer
// This means that RTLSDR is currently overwriting the MODES_ASYNC_BUF_NUMBER+1
// buffer, but we havent yet processed it, so we're going to lose it. There
// isn't much we can do to recover the lost data, but we can correct things to
// avoid any additional problems.
Modes.iDataOut = (MODES_ASYNC_BUF_NUMBER-1) & (Modes.iDataOut+1);
Modes.iDataReady = (MODES_ASYNC_BUF_NUMBER-1);
Modes.iDataLost++;
}
// Signal to the other thread that new data is ready, and unlock
pthread_cond_signal(&Modes.data_cond);
pthread_mutex_unlock(&Modes.data_mutex);
}
@ -268,13 +291,12 @@ void rtlsdrCallback(unsigned char *buf, uint32_t len, void *ctx) {
//
void readDataFromFile(void) {
pthread_mutex_lock(&Modes.data_mutex);
while(1) {
while(Modes.exit == 0) {
ssize_t nread, toread;
unsigned char *p;
if (Modes.exit == 1) break;
if (Modes.data_ready) {
pthread_cond_wait(&Modes.data_cond,&Modes.data_mutex);
if (Modes.iDataReady) {
pthread_cond_wait(&Modes.data_cond, &Modes.data_mutex);
continue;
}
@ -287,7 +309,7 @@ void readDataFromFile(void) {
}
toread = MODES_ASYNC_BUF_SIZE;
p = (unsigned char *) Modes.data;
p = (unsigned char *) Modes.pFileData;
while(toread) {
nread = read(Modes.fd, p, toread);
if (nread <= 0) {
@ -301,7 +323,17 @@ void readDataFromFile(void) {
// Not enough data on file to fill the buffer? Pad with no signal.
memset(p,127,toread);
}
Modes.data_ready = 1;
Modes.iDataIn &= (MODES_ASYNC_BUF_NUMBER-1); // Just incase!!!
// Get the system time for this block
ftime(&Modes.stSystemTimeRTL[Modes.iDataIn]);
// Queue the new data
Modes.pData[Modes.iDataIn] = Modes.pFileData;
Modes.iDataIn = (MODES_ASYNC_BUF_NUMBER-1) & (Modes.iDataIn + 1);
Modes.iDataReady = (MODES_ASYNC_BUF_NUMBER-1) & (Modes.iDataIn - Modes.iDataOut);
// Signal to the other thread that new data is ready
pthread_cond_signal(&Modes.data_cond);
}
@ -323,7 +355,6 @@ void *readerThreadEntryPoint(void *arg) {
readDataFromFile();
}
// Signal to the other thread that new data is ready - dummy really so threads don't mutually lock
Modes.data_ready = 1;
pthread_cond_signal(&Modes.data_cond);
pthread_mutex_unlock(&Modes.data_mutex);
#ifndef _WIN32
@ -561,10 +592,6 @@ int main(int argc, char **argv) {
// Initialization
modesInit();
//if (Modes.debug & MODES_DEBUG_BADCRC) {
// testAndTimeBitCorrection();
//}
if (Modes.net_only) {
fprintf(stderr,"Net-only mode, no RTL device or file open.\n");
} else if (Modes.filename == NULL) {
@ -589,31 +616,55 @@ int main(int argc, char **argv) {
// Create the thread that will read the data from the device.
pthread_create(&Modes.reader_thread, NULL, readerThreadEntryPoint, NULL);
pthread_mutex_lock(&Modes.data_mutex);
while(1) {
if (!Modes.data_ready) {
pthread_cond_wait(&Modes.data_cond,&Modes.data_mutex);
continue;
while (Modes.exit == 0) {
if (Modes.iDataReady == 0) {
pthread_cond_wait(&Modes.data_cond,&Modes.data_mutex); // This unlocks Modes.data_mutex, and waits for Modes.data_cond
continue; // Once (Modes.data_cond) occurs, it locks Modes.data_mutex
}
computeMagnitudeVector();
Modes.stSystemTimeBlk = Modes.stSystemTimeRTL;
// Signal to the other thread that we processed the available data
// and we want more (useful for --ifile)
Modes.data_ready = 0;
pthread_cond_signal(&Modes.data_cond);
// Modes.data_mutex is Locked, and (Modes.iDataReady != 0)
if (Modes.iDataReady) { // Check we have new data, just in case!!
Modes.iDataOut &= (MODES_ASYNC_BUF_NUMBER-1); // Just incase
// Translate the next lot of I/Q samples into Modes.magnitude
computeMagnitudeVector(Modes.pData[Modes.iDataOut]);
Modes.stSystemTimeBlk = Modes.stSystemTimeRTL[Modes.iDataOut];
// Update the input buffer pointer queue
Modes.iDataOut = (MODES_ASYNC_BUF_NUMBER-1) & (Modes.iDataOut + 1);
Modes.iDataReady = (MODES_ASYNC_BUF_NUMBER-1) & (Modes.iDataIn - Modes.iDataOut);
// If we lost some blocks, correct the timestamp
if (Modes.iDataLost) {
Modes.timestampBlk += (MODES_ASYNC_BUF_SAMPLES * 6 * Modes.iDataLost);
uRtlLost+= Modes.iDataLost;
Modes.iDataLost = 0;
}
// It's safe to release the lock now
pthread_cond_signal (&Modes.data_cond);
pthread_mutex_unlock(&Modes.data_mutex);
// Process data after releasing the lock, so that the capturing
// thread can read data while we perform computationally expensive
// stuff at the same time.
detectModeS(Modes.magnitude, MODES_ASYNC_BUF_SAMPLES);
// Update the timestamp ready for the next block
Modes.timestampBlk += (MODES_ASYNC_BUF_SAMPLES*6);
} else {
pthread_cond_signal (&Modes.data_cond);
pthread_mutex_unlock(&Modes.data_mutex);
}
// Process data after releasing the lock, so that the capturing
// thread can read data while we perform computationally expensive
// stuff * at the same time. (This should only be useful with very
// slow processors).
pthread_mutex_unlock(&Modes.data_mutex);
detectModeS(Modes.magnitude, MODES_ASYNC_BUF_SAMPLES);
Modes.timestampBlk += (MODES_ASYNC_BUF_SAMPLES*6);
backgroundTasks();
pthread_mutex_lock(&Modes.data_mutex);
if (Modes.exit) break;
}
// If --stats were given, print statistics
@ -658,7 +709,11 @@ int main(int argc, char **argv) {
pthread_cond_destroy(&Modes.data_cond); // Thread cleanup
pthread_mutex_destroy(&Modes.data_mutex);
pthread_join(Modes.reader_thread,NULL); // Wait on reader thread exit
#ifndef _WIN32
pthread_exit(0);
#else
return (0);
#endif
}
//
//=========================================================================