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Improvements to the main decoder

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* change symbol memory down to 60 (more is not needed)
 * change sample buffer to 40 seconds (improves decode accuracy)
 * Improve missed/extra seconds problem as ToS changes
 * Get rid of check_minute, decode_minute can do it
 * Check for BCD coding errors
 * Add conversion into UNIX time & local time
This commit is contained in:
Jeff Epler 2021-10-24 19:57:42 -05:00
parent ff3bd84c06
commit d5b4e2e2e0
1 changed files with 125 additions and 28 deletions
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153
decoder.cc
View file

@ -2,9 +2,17 @@
//
// SPDX-License-Identifier: GPL-3.0-only
#ifndef MAIN
#define NDEBUG
#endif
#define _DEFAULT_SOURCE
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <ctime>
// An efficient circular buffer of N bits. This is used to store the sampled
// WWVB signal for statistical purposes. It's also used as the basis of the
@ -54,9 +62,8 @@ template <int N, int M> struct circular_symbol_array {
return result;
}
bool put(int v0) {
bool put(int v) {
int result = 0;
int v = v0;
for (int j = 0; j < M; j++) {
result = (result << 1) | data.put(v & (1 << (M - 1)));
v <<= 1;
@ -70,12 +77,13 @@ template <int N, int M> struct circular_symbol_array {
// The second is divided into units of SUBSEC
constexpr size_t SUBSEC = 50;
// This many WWVB symbols are accumulated
constexpr size_t SYMBOLS = 125;
constexpr size_t SYMBOLS = 60;
// This many raw samples are accumulated. A slight code-size-savings is had
// if it is 2*SYMBOLS. But, it must also be a multiple of SUBSEC, so that the
// sample that 'falls out' of the buffer each time is the correct one to
// subtract from the 'counts array!
constexpr size_t BUFFER = 2 * SYMBOLS;
// subtract from the 'counts array! However, only ~5 seconds is too little
// history and it makes SoS wander too much, so go for 60 seconds instead.
constexpr size_t BUFFER = SUBSEC * 40;
static_assert(BUFFER % SUBSEC == 0);
// Raw samples from the receiver
@ -88,6 +96,7 @@ int16_t subsec = 0, sos = 0;
// Decoded symbols
circular_symbol_array<SYMBOLS, 2> symbols;
size_t tss; // time since second
// Receive a sample `b` from the receiver and process:
// * update statistics (counts and edges) incrementally
// * check all edges values to update the start-of-second value
@ -120,7 +129,22 @@ bool update(bool b) {
subsec = subsec1;
return subsec == sos;
bool result = false;
// If it's been a long time since the last second, fake one.
if (tss > SUBSEC + 2) {
result = true;
} else if (tss > SUBSEC / 2) {
// Otherwise, sos may be wandering, so don't repeat a second too soon
result = subsec == sos;
}
// either reset or increment time-since-second
if (result)
tss = 0;
else
tss++;
return result;
}
// Return how many items from i..j in the raw data array are true
@ -148,30 +172,24 @@ int decode_symbol() {
return 0;
}
// We know that the symbol just seen is a 2, which is a minute-terminating
// symbol. Check if all 2-markers of a minute are present.
bool check_minute() {
return symbols.at(SYMBOLS - 60 + 0) == 2 &&
symbols.at(SYMBOLS - 60 + 9) == 2 &&
symbols.at(SYMBOLS - 60 + 19) == 2 &&
symbols.at(SYMBOLS - 60 + 29) == 2 &&
symbols.at(SYMBOLS - 60 + 39) == 2 &&
symbols.at(SYMBOLS - 60 + 49) == 2;
}
// I guess we need to represent time...
struct wwvb_minute {
int16_t yday;
int8_t year, hour, minute;
int8_t ly, dst;
int8_t month, mday;
};
// Simple BCD-decoder
bool bcderr;
int decode_bcd(int d, int c = -1, int b = -1, int a = -1) {
return (a >= 0 ? (symbols.at(SYMBOLS - 60 + a) * 8) : 0) +
(b >= 0 ? (symbols.at(SYMBOLS - 60 + b) * 4) : 0) +
(c >= 0 ? (symbols.at(SYMBOLS - 60 + c) * 2) : 0) +
symbols.at(SYMBOLS - 60 + d) * 1;
int r = (a >= 0 ? (symbols.at(SYMBOLS - 60 + a) * 8) : 0) +
(b >= 0 ? (symbols.at(SYMBOLS - 60 + b) * 4) : 0) +
(c >= 0 ? (symbols.at(SYMBOLS - 60 + c) * 2) : 0) +
symbols.at(SYMBOLS - 60 + d) * 1;
if (r > 9)
bcderr = true;
return r;
}
template <class... Ints>
@ -179,22 +197,77 @@ int decode_bcd(int d, int c, int b, int a, Ints... rest) {
return decode_bcd(d, c, b, a) + 10 * decode_bcd(rest...);
}
// barebones decoding of some minute-fields, doesn't track bad BCD codes
// barebones decoding of some minute-fields
bool decode_minute(wwvb_minute &m) {
for (int i = 0; i < 60; i++) {
int sym = symbols.at(SYMBOLS - 60 + i);
bool is_mark = (i == 0) || (i % 10 == 9);
if (is_mark != (sym == 2))
return false;
bool is_zero = (i % 10 == 4) || i == 10 || i == 11 || i == 20 ||
i == 21 || i == 35;
if (is_zero && sym != 0)
return false;
}
bcderr = false;
m.year = decode_bcd(53, 52, 51, 50, 48, 47, 46, 45);
m.yday = decode_bcd(33, 32, 31, 30, 28, 27, 26, 25, 23, 22);
m.hour = decode_bcd(18, 17, 16, 15, 13, 12);
m.minute = decode_bcd(8, 7, 6, 5, 3, 2, 1);
m.ly = decode_bcd(55);
m.dst = decode_bcd(58, 57);
return true;
return !bcderr;
}
time_t wwvb_to_utc(const wwvb_minute &m) {
struct tm tm = {};
tm.tm_year = 2000 + m.year;
tm.tm_mday = 1;
time_t t = mktime(&tm);
t += (m.yday - 1) * 86400 + m.hour * 3600 + m.minute * 60;
return t;
}
struct tm apply_zone_and_dst(const wwvb_minute &m, int zone_offset,
bool observe_dst) {
auto t = wwvb_to_utc(m);
t -= zone_offset * 3600;
struct tm tm;
gmtime_r(&t, &tm);
switch (m.dst) {
case 0: // Standard time in effect
observe_dst = false;
break;
case 1: // DST ending at
{
struct tm tt = tm;
tt.tm_hour = 1; // DST ends at 2AM *DST* which is 1AM *standard*
auto u = mktime(&tt);
if (t >= u)
observe_dst = false;
}
break;
case 2: // DST starting at 2AM local time this day
{
struct tm tt = tm;
tt.tm_hour = 2;
auto u = mktime(&tt);
if (t < u)
observe_dst = false;
}
}
if (observe_dst)
t += 3600;
gmtime_r(&t, &tm);
return tm;
}
#if MAIN
@ -203,19 +276,43 @@ using namespace std;
int main() {
for (int c, i = -1; (c = cin.get()) != EOF; i++) {
static char zone[] = "TZ=UTC";
putenv(zone);
tzset();
int i = 0, si = 0, d = 0;
for (int c; (c = cin.get()) != EOF;) {
if (c != '_' && c != '#') {
continue;
}
if (update(c == '_')) {
int sym = decode_symbol();
symbols.put(sym);
if (sym == 2 && check_minute()) {
si++;
// std::cout << sym;
// if(si % 60 == 0) std::cout << "\n";
if (sym == 2) {
// This mark could be the minute-ending mark, so try to
// decode a minute
wwvb_minute m;
if (decode_minute(m)) {
std::cerr << "[" << i / 50. << "] " << (2000 + m.year)
<< " " << m.yday << " " << +m.hour << ":"
<< +m.minute << " " << +m.ly << +m.dst << "\n";
d++;
time_t t = wwvb_to_utc(m);
struct tm tt;
gmtime_r(&t, &tt);
printf("[%7.2f] %4d-%02d-%02d %2d:%02d %d %d\n", i / 50.,
tt.tm_year, tt.tm_mon + 1, tt.tm_mday, tt.tm_hour,
tt.tm_min, m.ly, m.dst);
tt = apply_zone_and_dst(m, 6, true);
printf(" %4d-%02d-%02d %2d:%02d\n", tt.tm_year,
tt.tm_mon + 1, tt.tm_mday, tt.tm_hour, tt.tm_min);
printf(" %4d-%03d %2d:%02d\n", m.year + 2000,
m.yday, m.hour, m.minute);
}
}
}
i++;
}
printf("Samples: %8d Symbols: %7d Minutes: %6d\n", i, si, d);
}
#endif