rtc_dcf77.c
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/* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
/* standard libraries */
#include <stdint.h> // standard integer types
#include <stdlib.h> // general utilities
/* STM32 (including CM3) libraries */
#include <libopencmsis/core_cm3.h> // Cortex M3 utilities
#include <libopencm3/cm3/nvic.h> // interrupt handler
#include <libopencm3/stm32/rcc.h> // real-time control clock library
#include <libopencm3/stm32/gpio.h> // general purpose input output library
#include <libopencm3/stm32/spi.h> // SPI library
#include <libopencm3/stm32/timer.h> // timer library
#include "rtc_dcf77.h" // RTC DCF77 library API
#include "global.h" // common methods
#define RTC_DCF77_ENABLE_PORT A
#define RTC_DCF77_ENABLE_PIN 2
#define RTC_DCF77_SIGNAL_PORT A
#define RTC_DCF77_SIGNAL_PIN 3
#define RTC_DCF77_TIMER 4
volatile bool rtc_dcf77_time_flag = false;
struct rtc_dcf77_time_t rtc_dcf77_time = {false, 0, 0, 0, 0, 0, 0, 0, 0};
static volatile uint64_t rtc_dcf77_frame = 0;
static uint8_t rtc_dcf77_bins[100] = {0};
static uint8_t rtc_dcf77_phase = 0;
static int16_t rtc_dcf77_phase_max = INT16_MIN;
static bool rtc_dcf77_phase_locked = false;
static uint8_t rtc_dcf77_invalid = 0;
#define RTC_DCF77_INVALID_MAX 5
void rtc_dcf77_setup(void)
{
// setup enable output
rcc_periph_clock_enable(RCC_GPIO(RTC_DCF77_ENABLE_PORT)); // enable clock GPIO peripheral
gpio_set_mode(GPIO(RTC_DCF77_ENABLE_PORT), GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO(RTC_DCF77_ENABLE_PIN)); // set pin to output push-pull to be able to enable the module
rtc_dcf77_off(); // disable module at start
// setup signal input
rcc_periph_clock_enable(RCC_GPIO(RTC_DCF77_SIGNAL_PORT)); // enable clock for signal input peripheral
gpio_set_mode(GPIO(RTC_DCF77_SIGNAL_PORT), GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, GPIO(RTC_DCF77_SIGNAL_PIN)); // set signal pin to input
// setup timer to sample signal at 1kHz
rcc_periph_clock_enable(RCC_TIM(RTC_DCF77_TIMER)); // enable clock for timer peripheral
timer_reset(TIM(RTC_DCF77_TIMER)); // reset timer state
timer_set_mode(TIM(RTC_DCF77_TIMER), TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP); // set timer mode, use undivided timer clock, edge alignment (simple count), and count up
timer_set_prescaler(TIM(RTC_DCF77_TIMER), 1); // set prescaler to divide frequency by two, to be able to have a period of 1 kHz (72MHz/2/2^16=549Hz<1kHz)
timer_set_period(TIM(RTC_DCF77_TIMER), rcc_ahb_frequency/2/1000-1); // set period to 1kHz (plus hand tuning)
timer_clear_flag(TIM(RTC_DCF77_TIMER), TIM_SR_UIF); // clear update event flag
timer_update_on_overflow(TIM(RTC_DCF77_TIMER)); // only use counter overflow as UEV source
timer_enable_irq(TIM(RTC_DCF77_TIMER), TIM_DIER_UIE); // enable update interrupt for timer
nvic_enable_irq(NVIC_TIM_IRQ(RTC_DCF77_TIMER)); // catch interrupt in service routine
}
void rtc_dcf77_on(void)
{
if (!gpio_get(GPIO(RTC_DCF77_ENABLE_PORT), GPIO(RTC_DCF77_ENABLE_PIN))) { // receiver is already turned on
return; // do nothing
}
rtc_dcf77_frame = 0; // reset frame
rtc_dcf77_phase_locked = false; // reset phase lock
rtc_dcf77_phase_max = INT16_MIN; // restart searching for phase
rtc_dcf77_invalid = 0; // reset invalid count
gpio_clear(GPIO(RTC_DCF77_ENABLE_PORT), GPIO(RTC_DCF77_ENABLE_PIN)); // enable module by pulling pin low
timer_set_counter(TIM(RTC_DCF77_TIMER), 0); // reset timer counter
timer_enable_counter(TIM(RTC_DCF77_TIMER)); // start timer to sample signal
}
void rtc_dcf77_off(void)
{
gpio_set(GPIO(RTC_DCF77_ENABLE_PORT), GPIO(RTC_DCF77_ENABLE_PIN)); // disable module by pull pin high
timer_disable_counter(TIM(RTC_DCF77_TIMER)); // stop timer since we don't need to sample anymore
}
static void rtc_dcf77_decode(void)
{
rtc_dcf77_time.valid = false; // reset validity
if (rtc_dcf77_frame==0) { // no time received yet
return;
}
if (!(rtc_dcf77_frame&((uint64_t)1<<20))) { // start of encoded time should always be 1
return;
}
// check minute parity
uint8_t parity = 0; // to check parity
for (uint8_t bit=21; bit<=28; bit++) {
if (rtc_dcf77_frame&((uint64_t)1<<bit)) {
parity++; // count the set bits
}
}
if (parity%2) { // parity should be even
return;
}
rtc_dcf77_time.minutes = 1*((rtc_dcf77_frame>>21)&(0x1))+2*((rtc_dcf77_frame>>22)&(0x1))+4*((rtc_dcf77_frame>>23)&(0x1))+8*((rtc_dcf77_frame>>24)&(0x1))+10*((rtc_dcf77_frame>>25)&(0x1))+20*((rtc_dcf77_frame>>26)&(0x1))+40*((rtc_dcf77_frame>>27)&(0x1)); // read minute (00-59)
if (rtc_dcf77_time.minutes>59) { // minutes should not be more than 59
return;
}
// check hour parity
parity = 0;
for (uint8_t bit=29; bit<=35; bit++) {
if (rtc_dcf77_frame&((uint64_t)1<<bit)) {
parity++; // count the set bits
}
}
if (parity%2) { // parity should be even
return;
}
rtc_dcf77_time.hours = 1*((rtc_dcf77_frame>>29)&(0x1))+2*((rtc_dcf77_frame>>30)&(0x1))+4*((rtc_dcf77_frame>>31)&(0x1))+8*((rtc_dcf77_frame>>32)&(0x1))+10*((rtc_dcf77_frame>>33)&(0x1))+20*((rtc_dcf77_frame>>34)&(0x1)); // read hour (00-23)
if (rtc_dcf77_time.hours>23) { // hours should not be more than 23
return;
}
// check date parity
parity = 0;
for (uint8_t bit=36; bit<=58; bit++) {
if (rtc_dcf77_frame&((uint64_t)1<<bit)) {
parity++; // count the set bits
}
}
if (parity%2) { // parity should be even
return;
}
rtc_dcf77_time.day = 1*((rtc_dcf77_frame>>36)&(0x1))+2*((rtc_dcf77_frame>>37)&(0x1))+4*((rtc_dcf77_frame>>38)&(0x1))+8*((rtc_dcf77_frame>>39)&(0x1))+10*((rtc_dcf77_frame>>40)&(0x1))+20*((rtc_dcf77_frame>>41)&(0x1)); // read day of the month (01-31)
if (rtc_dcf77_time.day==0 || rtc_dcf77_time.day>31) { // day of the month should be 1-31
return;
}
rtc_dcf77_time.weekday = 1*((rtc_dcf77_frame>>42)&(0x1))+2*((rtc_dcf77_frame>>43)&(0x1))+4*((rtc_dcf77_frame>>44)&(0x1)); // read day of the week (1=Monday - 7=Sunday)
if (rtc_dcf77_time.weekday==0 || rtc_dcf77_time.weekday>7) { // day of the week should be 1-7
return;
}
rtc_dcf77_time.month = 1*((rtc_dcf77_frame>>45)&(0x1))+2*((rtc_dcf77_frame>>46)&(0x1))+4*((rtc_dcf77_frame>>47)&(0x1))+8*((rtc_dcf77_frame>>48)&(0x1))+10*((rtc_dcf77_frame>>49)&(0x1)); // read month of the year (01-12)
if (rtc_dcf77_time.month==0 || rtc_dcf77_time.month>12) { // month of the year should be 1-12
return;
}
rtc_dcf77_time.year = 1*((rtc_dcf77_frame>>50)&(0x1))+2*((rtc_dcf77_frame>>51)&(0x1))+4*((rtc_dcf77_frame>>52)&(0x1))+8*((rtc_dcf77_frame>>53)&(0x1))+10*((rtc_dcf77_frame>>54)&(0x1))+20*((rtc_dcf77_frame>>55)&(0x1))+40*((rtc_dcf77_frame>>56)&(0x1))+80*((rtc_dcf77_frame>>57)&(0x1)); // read year of the century (00-99)
if (rtc_dcf77_time.year>99) { // year should be <100
return;
}
rtc_dcf77_time.valid = true; // if we managed it until here the decoding is successful
}
static void rtc_dcf77_phase_detector(void) {
uint8_t integral_i = 0; // which bin has the highest integral/correlation
int16_t integral_max = 0; // maximum integral value found
for (uint8_t start=0; start<(rtc_dcf77_phase_locked ? 10 : LENGTH(rtc_dcf77_bins)); start++) { // which bin has been used to start the convolution (only use +/- 15 bits of previous phase if locked)
int16_t integral = 0; // value of the integral
for (uint8_t bin=0; bin<LENGTH(rtc_dcf77_bins); bin++) { // go through bins to calculate correlation
int8_t dfc77_signal = -1; // the signal of the reference DCF77 signal
if (bin<10) { // the signal is always high for the first 100 ms
dfc77_signal = 1; // use highest values
} else if (bin<20) { // the signal has 50% chance of being high for the next 100 ms (encoding the bit)
dfc77_signal = 0; // use middle value
}
// the rest of the time the signal is low (keep lowest value)
integral += rtc_dcf77_bins[(start+bin+rtc_dcf77_phase+LENGTH(rtc_dcf77_bins)-5)%LENGTH(rtc_dcf77_bins)]*dfc77_signal; // calculate the correlation at this point and integrate it (start with previous phase - 15 bins)
}
if (integral>integral_max) { // we found a better correlation result
integral_max = integral; // save new best result
integral_i = (start+rtc_dcf77_phase+LENGTH(rtc_dcf77_bins)-5)%LENGTH(rtc_dcf77_bins); // start new best phase start
}
}
if ((int16_t)(integral_max+40)>rtc_dcf77_phase_max) { // only save new phase if it is better than the last one, with some margin to compensate for the drift (perfect correlation = 100, worst correlation = -800)
rtc_dcf77_phase_max = integral_max; // save best phase value
rtc_dcf77_phase = integral_i; // save bin index corresponding to start of the phase
}
}
void TIM_ISR(RTC_DCF77_TIMER)(void)
{
static uint8_t bin_state = 0; // how many samples have been stored in the bin
static uint8_t bin_i = 0; // current bin filled
static uint8_t bit_i = 0; // current bit in the DCF77 minute frame
if (timer_get_flag(TIM(RTC_DCF77_TIMER), TIM_SR_UIF)) { // overflow update event happened
timer_clear_flag(TIM(RTC_DCF77_TIMER), TIM_SR_UIF); // clear flag
// fill bin with current sample state
if (gpio_get(GPIO(RTC_DCF77_SIGNAL_PORT), GPIO(RTC_DCF77_SIGNAL_PIN))) {
rtc_dcf77_bins[bin_i]++; // only need to increase if the signal is high
}
bin_state++; // remember we filled the bin
if (bin_state>=10) { // bin has 10x1 ms samples, it is now full
bin_i = (bin_i+1)%LENGTH(rtc_dcf77_bins); // go to next bin
rtc_dcf77_bins[bin_i] = 0; // restart bin
bin_state = 0; // restart collecting
}
if (0==bin_i && 0==bin_state) { // we have 1 s of samples
if (bit_i<59) {
rtc_dcf77_phase_detector(); // detect phase in signal
// check modulation of first 100 ms
uint16_t modulation = 0;
for (uint8_t bin=0; bin<10; bin++) {
modulation += rtc_dcf77_bins[(rtc_dcf77_phase+bin)%LENGTH(rtc_dcf77_bins)];
}
if (modulation<50) { // signal is not modulated, it might be the 60th pause bit
bit_i = 0; // restart frame
rtc_dcf77_frame = 0; // restart frame
rtc_dcf77_phase_max = INT16_MIN; // restart searching for phase
rtc_dcf77_phase_locked = false; // unlock phase since the decoding seems wrong
} else { // modulation detected
// check modulation of next 100 ms
modulation = 0;
for (uint8_t bin=10; bin<20; bin++) {
modulation += rtc_dcf77_bins[(rtc_dcf77_phase+bin)%LENGTH(rtc_dcf77_bins)];
}
if (modulation<50) { // it's a 0
// bit is already cleared
} else { // it's a 1
rtc_dcf77_frame |= (1ULL<<bit_i); // set bit
}
bit_i++; // go to next bit
}
} else { // complete DCF77 frame received
rtc_dcf77_decode(); // decode frame
if (rtc_dcf77_time.valid) { // decoded time is valid
rtc_dcf77_time.milliseconds = rtc_dcf77_phase*10; // save milliseconds corresponding to phase
rtc_dcf77_phase_locked = true; // lock phase since decoding succeeded
rtc_dcf77_invalid = 0; // remember we had an valid decoding
rtc_dcf77_time_flag = true; // notify user we have time
} else {
rtc_dcf77_invalid++; // remember we had an invalid decoding
}
if (rtc_dcf77_invalid>=RTC_DCF77_INVALID_MAX) { // too many invalid decoding
rtc_dcf77_off(); // switch off receiver so it can re-tune
}
bit_i = 0; // restart frame
rtc_dcf77_frame = 0; // restart frame
}
}
} else { // no other interrupt should occur
while (true); // unhandled exception: wait for the watchdog to bite
}
}
RTC_DCF77_ENABLE_PIN
#define RTC_DCF77_ENABLE_PIN
GPIO pinto enable the module.
Definition: rtc_dcf77.c:41
rtc_dcf77_phase_detector
static void rtc_dcf77_phase_detector(void)
find phase of 1 seconds DCF77 signal in the bins searches the complete second for the highest correla...
Definition: rtc_dcf77.c:192
TIM_ISR
#define TIM_ISR(x)
get interrupt service routine for timer base on TIM identifier
Definition: global.h:113
RCC_GPIO
#define RCC_GPIO(x)
get RCC for GPIO based on GPIO identifier
Definition: global.h:105
rtc_dcf77_phase_locked
static bool rtc_dcf77_phase_locked
if the current phase has been verified
Definition: rtc_dcf77.c:64
NVIC_TIM_IRQ
#define NVIC_TIM_IRQ(x)
get NVIC IRQ for timer base on TIM identifier
Definition: global.h:111
rtc_dcf77_time_t::minutes
uint8_t minutes
minutes (00-49)
Definition: rtc_dcf77.h:31
rtc_dcf77_setup
void rtc_dcf77_setup(void)
setup DCF77 time receiver module
Definition: rtc_dcf77.c:70
RTC_DCF77_SIGNAL_PORT
#define RTC_DCF77_SIGNAL_PORT
GPIO port to capture the DCF signal.
Definition: rtc_dcf77.c:42
global.h
global definitions and methods (API)
GPIO
#define GPIO(x)
get GPIO based on GPIO identifier
Definition: global.h:103
rtc_dcf77_off
void rtc_dcf77_off(void)
switch off DCF77 time receiver module
Definition: rtc_dcf77.c:107
rtc_dcf77_phase_max
static int16_t rtc_dcf77_phase_max
the maximum phase value
Definition: rtc_dcf77.c:62
RCC_TIM
#define RCC_TIM(x)
get RCC for timer based on TIM identifier
Definition: global.h:109
rtc_dcf77_time_t::month
uint8_t month
month (01-12)
Definition: rtc_dcf77.h:35
rtc_dcf77_time_t
decoded DCF77 time received
Definition: rtc_dcf77.h:27
RTC_DCF77_ENABLE_PORT
#define RTC_DCF77_ENABLE_PORT
GPIO port to enable the module.
Definition: rtc_dcf77.c:40
rtc_dcf77_phase
static uint8_t rtc_dcf77_phase
the bin shift for the bit phase
Definition: rtc_dcf77.c:60
RTC_DCF77_INVALID_MAX
#define RTC_DCF77_INVALID_MAX
maximum number of invalid decoding before switching off
Definition: rtc_dcf77.c:68
rtc_dcf77_time_flag
volatile bool rtc_dcf77_time_flag
set when time information has been received
Definition: rtc_dcf77.c:52
rtc_dcf77_time
struct rtc_dcf77_time_t rtc_dcf77_time
the received DCF77 frame bits
Definition: rtc_dcf77.c:53
RTC_DCF77_SIGNAL_PIN
#define RTC_DCF77_SIGNAL_PIN
GPIO pin to capture the DCF signal.
Definition: rtc_dcf77.c:43
rtc_dcf77_time_t::hours
uint8_t hours
hours (00-23)
Definition: rtc_dcf77.h:32
rtc_dcf77_time_t::weekday
uint8_t weekday
day of the week (1-7=Monday-Sunday)
Definition: rtc_dcf77.h:34
rtc_dcf77_time_t::valid
bool valid
if the time is valid
Definition: rtc_dcf77.h:28
rtc_dcf77_time_t::year
uint8_t year
year within century (00-99)
Definition: rtc_dcf77.h:36
LENGTH
#define LENGTH(x)
get the length of an array
Definition: global.h:26
RTC_DCF77_TIMER
#define RTC_DCF77_TIMER
timer peripheral
Definition: rtc_dcf77.c:49
rtc_dcf77_time_t::day
uint8_t day
day of the month (01-31)
Definition: rtc_dcf77.h:33
TIM
#define TIM(x)
get TIM based on TIM identifier
Definition: global.h:107
rtc_dcf77.h
library to get time from a DCF77 module (API)
rtc_dcf77_decode
static void rtc_dcf77_decode(void)
decode rtc_dcf77_frame DCF77 frame into rtc_dcf77_time DCF77 time
Definition: rtc_dcf77.c:116
rtc_dcf77_bins
static uint8_t rtc_dcf77_bins[100]
values of the DCF77 signal over 10 ms for 1 s (how many times it is high)
Definition: rtc_dcf77.c:58
rtc_dcf77_time_t::milliseconds
uint8_t milliseconds
milliseconds (00-99)
Definition: rtc_dcf77.h:29
rtc_dcf77_invalid
static uint8_t rtc_dcf77_invalid
number of invalid decoding
Definition: rtc_dcf77.c:66
rtc_dcf77_on
void rtc_dcf77_on(void)
switch on DCF77 time receiver module
Definition: rtc_dcf77.c:93