FGFS-4.1/gr-air-modes
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Split the int timestamp from frac timestamp so you don't lose precision when using, say, UTC time. Cleaned up some cruft while I was at it. This also allows devices which don't have timestamps to tag based on samples elapsed since the flowgraph started.

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This commit is contained in:
Nick Foster
2012-12-12 17:40:01 -08:00
parent 3be6e9fd6e
commit 1e2b8a4f46
9 changed files with 68 additions and 76 deletions
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45
lib/air_modes_preamble.cc
View File

@@ -78,20 +78,31 @@ static double correlate_preamble(const float *in, int samples_per_chip) {
return corr;
}
//todo: make it return a pair of some kind, otherwise you can lose precision
static double tag_to_timestamp(gr_tag_t tstamp, uint64_t abs_sample_cnt, double secs_per_sample) {
//takes an rx tag and issues a tag offset appropriately for the preamble
static const pmt::pmt_t offset_stamp(const gr_tag_t &tstamp, const uint64_t abs_sample_cnt, const double secs_per_sample) {
uint64_t ts_sample, last_whole_stamp;
double last_frac_stamp;
if(tstamp.key == NULL || pmt::pmt_symbol_to_string(tstamp.key) != "rx_time") return 0;
last_whole_stamp = pmt::pmt_to_uint64(pmt::pmt_tuple_ref(tstamp.value, 0));
last_frac_stamp = pmt::pmt_to_double(pmt::pmt_tuple_ref(tstamp.value, 1));
ts_sample = tstamp.offset;
if(tstamp.key == NULL || pmt::pmt_symbol_to_string(tstamp.key) != "rx_time") {
last_whole_stamp = 0;
last_frac_stamp = 0;
ts_sample = 0;
} else {
last_whole_stamp = pmt::pmt_to_uint64(pmt::pmt_tuple_ref(tstamp.value, 0));
last_frac_stamp = pmt::pmt_to_double(pmt::pmt_tuple_ref(tstamp.value, 1));
ts_sample = tstamp.offset;
}
double tstime = double(abs_sample_cnt * secs_per_sample) + last_whole_stamp + last_frac_stamp;
if(0) std::cout << "HEY WE GOT A STAMP AT " << tstime << " TICKS AT SAMPLE " << ts_sample << " ABS SAMPLE CNT IS " << abs_sample_cnt << std::endl;
return tstime;
double fractime = double(abs_sample_cnt * secs_per_sample) + last_frac_stamp;
last_whole_stamp += int(fractime);
fractime -= int(fractime);
const pmt::pmt_t newval = pmt::pmt_make_tuple(
pmt::pmt_from_uint64(last_whole_stamp),
pmt::pmt_from_double(fractime)
);
return newval;
}
int air_modes_preamble::general_work(int noutput_items,
@@ -186,16 +197,14 @@ int air_modes_preamble::general_work(int noutput_items,
integrate_and_dump(out, &in[i], 240, d_samples_per_chip);
}
//get the timestamp of the preamble
double tstamp = tag_to_timestamp(d_timestamp, abs_sample_cnt + i, d_secs_per_sample);
const pmt::pmt_t new_pmt = offset_stamp(d_timestamp, abs_sample_cnt + i, d_secs_per_sample);
//now tag the preamble
add_item_tag(0, //stream ID
nitems_written(0), //sample
d_key, //frame_info
pmt::pmt_from_double(tstamp),
d_me //block src id
);
nitems_written(0), //sample
d_key, //frame_info
new_pmt,
d_me //block src id
);
//std::cout << "PREAMBLE" << std::endl;

66
lib/air_modes_slicer.cc
View File

@@ -112,84 +112,80 @@ int air_modes_slicer::work(int noutput_items,
for(tag_iter = tags.begin(); tag_iter != tags.end(); tag_iter++) {
uint64_t i = tag_iter->offset - abs_sample_cnt;
modes_packet rx_packet;
memset(&rx_packet.data, 0x00, 14 * sizeof(unsigned char));
memset(&rx_packet.lowconfbits, 0x00, 24 * sizeof(unsigned char));
rx_packet.numlowconf = 0;
memset(&d_data, 0x00, 14 * sizeof(unsigned char));
memset(&d_lowconfbits, 0x00, 24 * sizeof(unsigned char));
unsigned int numlowconf = 0;
//let's use the preamble to get a reference level for the packet
//fixme: a better thing to do is create a bi-level avg 1 and avg 0
//through simple statistics, then take the median for your slice level
//this won't improve decoding but will improve confidence
rx_packet.reference_level = (in[i]
+ in[i+2]
+ in[i+7]
+ in[i+9]) / 4.0;
double reference_level = (in[i]
+ in[i+2]
+ in[i+7]
+ in[i+9]) / 4.0;
i += 16; //move on up to the first bit of the packet data
//now let's slice the header so we can determine if it's a short pkt or a long pkt
unsigned char pkt_hdr = 0;
for(int j=0; j < 5; j++) {
slice_result_t slice_result = slicer(in[i+j*2], in[i+j*2+1], rx_packet.reference_level);
slice_result_t slice_result = slicer(in[i+j*2], in[i+j*2+1], reference_level);
if(slice_result.decision) pkt_hdr += 1 << (4-j);
}
if(pkt_hdr == 16 or pkt_hdr == 17 or pkt_hdr == 20 or pkt_hdr == 21) rx_packet.type = Long_Packet;
else rx_packet.type = Short_Packet;
int packet_length = (rx_packet.type == framer_packet_type(Short_Packet)) ? 56 : 112;
framer_packet_type type;
if(pkt_hdr == 16 or pkt_hdr == 17 or pkt_hdr == 20 or pkt_hdr == 21) type = Long_Packet;
else type = Short_Packet;
int packet_length = (type == Short_Packet) ? 56 : 112;
//it's slice time!
//TODO: don't repeat your work here, you already have the first 5 bits
slice_result_t slice_result;
for(int j = 0; j < packet_length; j++) {
slice_result_t slice_result = slicer(in[i+j*2], in[i+j*2+1], rx_packet.reference_level);
slice_result = slicer(in[i+j*2], in[i+j*2+1], reference_level);
//put the data into the packet
if(slice_result.decision) {
rx_packet.data[j/8] += 1 << (7-(j%8));
d_data[j/8] += 1 << (7-(j%8));
}
//put the confidence decision into the packet
if(slice_result.confidence) {
//rx_packet.confidence[j/8] += 1 << (7-(j%8));
//d_confidence[j/8] += 1 << (7-(j%8));
} else {
if(rx_packet.numlowconf < 24) rx_packet.lowconfbits[rx_packet.numlowconf++] = j;
if(numlowconf < 24) d_lowconfbits[numlowconf++] = j;
}
}
/******************** BEGIN TIMESTAMP BS ******************/
rx_packet.timestamp = pmt_to_double(tag_iter->value);
/******************* END TIMESTAMP BS *********************/
//increment for the next round
uint64_t timestamp_secs = pmt::pmt_to_uint64(pmt::pmt_tuple_ref(tag_iter->value, 0));
double timestamp_frac = pmt::pmt_to_double(pmt::pmt_tuple_ref(tag_iter->value, 1));
//here you might want to traverse the whole packet and if you find all 0's, just toss it. don't know why these packets turn up, but they pass ECC.
bool zeroes = 1;
for(int m = 0; m < 14; m++) {
if(rx_packet.data[m]) zeroes = 0;
if(d_data[m]) zeroes = 0;
}
if(zeroes) {continue;} //toss it
rx_packet.message_type = (rx_packet.data[0] >> 3) & 0x1F; //get the message type to make decisions on ECC methods
unsigned int message_type = (d_data[0] >> 3) & 0x1F; //get the message type to make decisions on ECC methods
if(rx_packet.type == Short_Packet && rx_packet.message_type != 11 && rx_packet.numlowconf > 0) {continue;}
if(rx_packet.message_type == 11 && rx_packet.numlowconf >= 10) {continue;}
if(type == Short_Packet && message_type != 11 && numlowconf > 0) {continue;}
if(message_type == 11 && numlowconf >= 10) {continue;}
rx_packet.crc = modes_check_crc(rx_packet.data, packet_length);
unsigned long crc = modes_check_crc(d_data, packet_length);
//crc for packets that aren't type 11 or type 17 is encoded with the transponder ID, which we don't know
//therefore we toss 'em if there's syndrome
//crc for the other short packets is usually nonzero, so they can't really be trusted that far
if(rx_packet.crc && (rx_packet.message_type == 11 || rx_packet.message_type == 17)) {continue;}
d_payload.str("");
if(crc && (message_type == 11 || message_type == 17)) {continue;}
std::ostringstream payload;
for(int m = 0; m < packet_length/8; m++) {
d_payload << std::hex << std::setw(2) << std::setfill('0') << unsigned(rx_packet.data[m]);
payload << std::hex << std::setw(2) << std::setfill('0') << unsigned(d_data[m]);
}
d_payload << " " << std::setw(6) << rx_packet.crc << " " << std::dec << rx_packet.reference_level
<< " " << std::setprecision(10) << std::setw(10) << rx_packet.timestamp;
gr_message_sptr msg = gr_make_message_from_string(std::string(d_payload.str()));
payload << " " << std::setw(6) << crc << " " << std::dec << reference_level
<< " " << timestamp_secs << " " << std::setprecision(20) << timestamp_frac;
gr_message_sptr msg = gr_make_message_from_string(std::string(payload.str()));
d_queue->handle(msg);
}
if(0) std::cout << "Slicer consumed " << size << ", returned " << size << std::endl;
return size;
}