CN110908272A - 1pps pulse signal timing method - Google Patents
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Abstract
The invention relates to a 1pps pulse signal timing method, belonging to the technical field of wireless communication networks. The invention mainly realizes the high-precision timing function of NMEA-0183+1pps on an STM32F407 platform. In synchronous systems, a 1pps PULSE (1PULSE PER SECOND PULSE output) is primarily used, which is a standard TTL logic output form, whose rising edge corresponds to time when the navigation output is active. The effect of the 1pps pulse is to use its rising edge as a time tick signal of the UTC time, and then to implement time synchronization by parsing the NMEA-0183 protocol.
Description
Technical Field
The invention relates to a 1pps pulse signal timing method, belonging to the technical field of wireless communication networks.
Background
Clocks are usually designed for low cost, but keeping accurate time is of secondary importance, even fairly accurate computer clocks can vary due to manufacturing defects, temperature variations, electromagnetic interference, age of the quartz crystal, and even system load variations. Furthermore, even with a time system where the error is small, the error may increase significantly over a long period of time.
In the early stage of the twentieth century, the short-wave radio broadcasting is implemented in the United states for the first time, under continuous tests, the time synchronization problem in most regions is finally solved, the precision is continuously broken through, and the millisecond level is achieved at present. In the next decades, the main means of time synchronization has been that short-wave radio broadcasting has not changed. Within decades of time synchronization technology evolution, the nature of clocks has evolved by orders of magnitude. Obviously, short-wave timing cannot meet the requirements of clock development. In the middle of the twentieth century, with the continuous improvement of the time synchronization technology, a navigation system named as-c long wave gradually went to the historical stage. The accuracy achieved by using such long waves as time synchronization techniques has entered the microsecond range, but this is far from sufficient for further development of production and research, since the accuracy of the system and the range it can cover is very limited. In the eighties of the twentieth century, the united states first established a global positioning system, followed by the former soviet union established a glonass global navigation satellite system. The satellite two-way comparison results formally entered international atomic Time (TAI) calculations at the end of the last century, which solved the path delay problem in order to improve the accuracy of time synchronization.
In the eighties of the twentieth century, the united states first established a global positioning system, followed by the former soviet union established a glonass global navigation satellite system. The satellite bidirectional comparison result formally enters international atomic Time (TAI) calculation at the end of the last century, which introduces a new idea for improving the precision of time synchronization and solving the problem of path delay.
Disclosure of Invention
The invention aims to provide a 1pps pulse signal timing method, which is used for solving the phenomena of travel time errors and the like of an STM32 internal clock and increasing the high-efficiency accuracy of the internal clock.
The technical scheme of the invention is as follows: a1 pps pulse signal timing method comprises the following specific steps:
step1, firstly, judging whether the GPS data reception is valid: judging whether the GPS data positioning is successful or not through a special statement in the NMEA-0183 protocol;
step2, judging whether a 1pps pulse exists: observing whether the 1pps pulse is input and effective through oscilloscope display, if so, indicating that the 1pps pulse exists, otherwise, indicating that the 1pps pulse does not exist;
step3, synchronizing RTC time in millisecond level: when the rising edge of the 1pps pulse comes, the pulse is considered to be UTC time, timing is started at the rising edge moment of the 1pps pulse, and the rising edge of the 1pps pulse is used for carrying out millisecond zero clearing on the system clock time at the moment, so that millisecond synchronization of the system clock is realized;
step4, keeping the RTC time at millisecond level: the specific time keeping method is mainly divided into two cases, and the detailed description is as follows:
(1) when the 1pps pulse signal never synchronizes the STM32, if the count value of the counter is greater than or equal to 1000, the counter is cleared, so that the time keeping is realized;
(2) when the GPS is synchronized with the STM32, but the signal is lost at the moment, no pulse signal of 1pps exists, and the counter is cleared when the value of the counter at the moment is greater than or equal to the value synchronized with the counter before;
step5, judging that the GPS data reception is finished: GPS data is received through a serial port, in the process of serial port data receiving, the data is received one by one in the form of bytes, when a byte is received, the global time carries out assignment once on the last data receiving time, namely the global time and the data receiving time are considered to be synchronous in the process of the assignment, when the serial port has no data to receive or the data receiving is stopped, the global time is accumulated all the time, at a certain moment, the global time is certainly greater than the value of the last data receiving time, if the global time is greater than the last data receiving time, the data is no longer received at the moment, and the data receiving at the moment is considered to be finished;
step6, synchronizing RTC time in second level: therefore, the time gap is visually observed to be between 220ms and 230ms on an oscilloscope according to a time sequence diagram of data receiving displayed by the oscilloscope through experiments, if the time gap is subtracted from the last data receiving time by the global time and is smaller than 225ms at the moment and a pulse signal of 1pps exists at the current moment, the system time is rounded, so that the time correction is realized, and if the time gap is subtracted from the last data receiving time by the global time and is larger than or equal to 225ms, the next data receiving gap is waited.
The specific steps of Step1 are as follows: and searching a character corresponding to the next designated position by using a character string search function and a protocol $ GPGSA, A, checking the positioning condition for judging the positioning effect, if the corresponding character is less than 3, considering that the positioning precision is insufficient or the positioning is not successful, namely the GPS data is invalid, and if the corresponding character is more than or equal to 3, considering that the positioning is successful, namely the GPS data is valid.
The invention has the beneficial effects that: the invention uses the rising edge of 1pps pulse as the time tick signal of UTC time, and then realizes time synchronization by analyzing the NMEA-0183 protocol. Compared with the prior art, the method mainly solves the problem of travel time error of the STM32 internal clock, increases the time accuracy of the internal clock, achieves millisecond synchronization of time, and eliminates travel time error.
Drawings
FIG. 1 is a general flow chart of the present invention;
FIG. 2 is a timing diagram of the GPS pulse-per-second synchronous timing principle;
FIG. 3 is a timing diagram of a second-level synchronous timekeeping sequence 1;
FIG. 4 is a timing diagram of a second-level synchronous timekeeping sequence 2;
fig. 5 is an overall flow chart of synchronization and timekeeping.
Detailed Description
The invention is further described with reference to the following drawings and detailed description.
Example 1: as shown in fig. 1-5, a timing method for a 1pps pulse signal includes the following steps:
step1, firstly, judging whether the GPS data reception is valid: judging whether the GPS data positioning is successful or not through a special statement in the NMEA-0183 protocol;
step2, judging whether a 1pps pulse exists: observing whether the 1pps pulse is input and effective through oscilloscope display, if so, indicating that the 1pps pulse exists, otherwise, indicating that the 1pps pulse does not exist;
step3, synchronizing RTC time in millisecond level: when the rising edge of the 1pps pulse comes, the pulse is considered to be UTC time, timing is started at the rising edge moment of the 1pps pulse, and the rising edge of the 1pps pulse is used for carrying out millisecond zero clearing on the system clock time at the moment, so that millisecond synchronization of the system clock is realized;
step4, keeping the RTC time at millisecond level: the specific time keeping method is mainly divided into two cases, and the detailed description is as follows:
(1) when the 1pps pulse signal never synchronizes the STM32, if the count value of the counter is greater than or equal to 1000, the counter is cleared, so that the time keeping is realized;
(2) when the GPS is synchronized with the STM32, but the signal is lost at the moment, no pulse signal of 1pps exists, and the counter is cleared when the value of the counter at the moment is greater than or equal to the value synchronized with the counter before;
step5, judging that the GPS data reception is finished: GPS data is received through a serial port, in the process of serial port data receiving, the data is received one by one in the form of bytes, when a byte is received, the global time carries out assignment once on the last data receiving time, namely the global time and the data receiving time are considered to be synchronous in the process of the assignment, when the serial port has no data to receive or the data receiving is stopped, the global time is accumulated all the time, at a certain moment, the global time is certainly greater than the value of the last data receiving time, if the global time is greater than the last data receiving time, the data is no longer received at the moment, and the data receiving at the moment is considered to be finished;
step6, synchronizing RTC time in second level: therefore, the time gap is visually observed to be between 220ms and 230ms on an oscilloscope according to a time sequence diagram of data receiving displayed by the oscilloscope through experiments, if the time gap is subtracted from the last data receiving time by the global time and is smaller than 225ms at the moment and a pulse signal of 1pps exists at the current moment, the system time is rounded, so that the time correction is realized, and if the time gap is subtracted from the last data receiving time by the global time and is larger than or equal to 225ms, the next data receiving gap is waited.
Further, the specific steps of Step1 are as follows: and searching a character corresponding to the next designated position by using a character string search function and a protocol $ GPGSA, A, checking the positioning condition for judging the positioning effect, if the corresponding character is less than 3, considering that the positioning precision is insufficient or the positioning is not successful, namely the GPS data is invalid, and if the corresponding character is more than or equal to 3, considering that the positioning is successful, namely the GPS data is valid.
Further, the millisecond timekeeping in Step4 is due to:
in practical application, the GPS synchronization timing function is affected by many external unavoidable factors to generate time errors, and these external factors causing the time errors are many, for example, the GPS satellite signal orientation changes, the GPS signal receiving antenna is interfered, the GPS receiving system is aged or fails due to year-round operation, and the like, which results in that the GPS receiver cannot receive signals and loses time synchronization in a short time. Therefore, in this case, it is necessary to establish a GPS time service system based on a GPS receiver with high stability and high accuracy
Further, the timing of the GPS data reception gap in Step6 is due to:
the RTC time is STM32 internal clock time, and the UTC time is standard time carried in GPS data. In the process of synchronizing RTC second-level time, particularly in the process of timing GPS data transmission gaps, the action of timing is not instantly realized in the process of data processing, a process is also needed, even the process time is hardly perceived by human eyes, but the time is actually existed, generally, the process of synchronizing also needs a certain time, in the GPS data receiving engineering, the system mainly works in the process of receiving GPS data, more time areas are reserved for timing, and if the timing work is needed, the timing work can only be started in the GPS data receiving gaps, so that the whole timing work can be finished at the next rising edge moment of 1pps pulse, and the accuracy of the timing time is ensured.
With specific reference to fig. 3, the timing diagram operation of fig. 4 is explained as follows:
1. the steps performed at time T1 are:
and the time value of the Globaltimer timer at the moment is recorded at the time T1, and the GPS data receiving serial port is cleared to prevent aliasing. The millisecond counter is cleared. And then waits for the end of data reception.
2. If the reception of the present piece of GPS data is just finished at time m1, the GPS data reception gap in this case encompasses the rising edge of the next pps pulse, i.e., time T2. The 8563 clock time is synchronized in seconds with the rising edge. Previously, the time for GPS data analysis and the time required for synchronization timing were measured. Suppose that the data analysis time is k, the time required by time correction is s, and the specific time needs to be measured. The timing operation is started s seconds before T3, and is completed at time T3.
3. The first condition is as follows: just after GPS data resolution, a 1pps pulse rising edge is encountered. As shown in timing diagram 3.
The timing operation is started s seconds before T3. The specific method is as follows:
after the GPS data is received, the time of the Globaimer timer is read again at the moment and compared with the time of the Globaimer extracted before, and whether the time difference between the two is within 1 second or not is judged. And whether the time left by the analyzed data in the gap is enough to carry out time correction work of the 8563 clock is checked.
i. If the remaining time is enough, the timing operation is carried out s seconds before the rising edge of the following pulse.
if the remaining time is not enough, the rising edge of the pulse is missed, and the timing operation is carried out at the rising edge moment of the next pulse
Directly assigning the GPS time plus one to the 8563 clock time if the two global time differences are within 1 second.
if the two global time differences are greater than 1 second, then the time difference is rounded down and then added with GPS time and then assigned with an assigned value of 8563 clock times.
Case two: if 1pps pulse is missed in the process of analyzing the GPS data. As shown in timing diagram 4, then: after the data analysis is finished, the difference between the time of the Globatimer timer extracted again and the time of the Globatimer extracted before is rounded, and the obtained number is the number of pps pulses missed. The timing begins s seconds between the rising edges of the pulses T3 by assigning the 8563 clock time at the next rising edge of the pulse after the GPS time plus the number of missed pps pulses plus 1. Thereby completing all timing work
4. After one data synchronization is performed, verification is required to determine whether the second-level synchronization of the 8563 clock is successful, and then a time comparison is required in the next GPS data reception slot. As shown in the timing chart of fig. 4, the next data reception is completed at time m3, that is, the next data reception slot is started. The 8563 clock time is read again at time m3 with the GPS clock time, after which a second order comparison is made. If the comparison results are the same, marking is finished at the time T4, and if the comparison results are not the same, the synchronous timing operation is repeated.
The invention mainly realizes the high-precision timing function of NMEA-0183+1pps on an STM32F407 platform. In synchronous systems, a 1pps PULSE (1PULSE PER SECOND PULSE output) is primarily used, which is a standard TTL logic output form, whose rising edge corresponds to time when the navigation output is active. The effect of the 1pps pulse is to use its rising edge as a time tick signal of the UTC time, and then to implement time synchronization by parsing the NMEA-0183 protocol.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit and scope of the present invention.
Claims (2)
1. A1 pps pulse signal timing method is characterized in that: the method comprises the following steps:
step1, firstly, judging whether the GPS data reception is valid: judging whether the GPS data positioning is successful or not through a special statement in the NMEA-0183 protocol;
step2, judging whether a 1pps pulse exists: observing whether the 1pps pulse is input and effective through oscilloscope display, if so, indicating that the 1pps pulse exists, otherwise, indicating that the 1pps pulse does not exist;
step3, synchronizing RTC time in millisecond level: when the rising edge of the 1pps pulse comes, the pulse is considered to be UTC time, timing is started at the rising edge moment of the 1pps pulse, and the rising edge of the 1pps pulse is used for carrying out millisecond zero clearing on the system clock time at the moment, so that millisecond synchronization of the system clock is realized;
step4, keeping the RTC time at millisecond level: the specific time keeping method is mainly divided into two cases, and the detailed description is as follows:
(1) when the 1pps pulse signal never synchronizes the STM32, if the count value of the counter is greater than or equal to 1000, the counter is cleared, so that the time keeping is realized;
(2) when the GPS is synchronized with the STM32, but the signal is lost at the moment, no pulse signal of 1pps exists, and the counter is cleared when the value of the counter at the moment is greater than or equal to the value synchronized with the counter before;
step5, judging that the GPS data reception is finished: GPS data is received through a serial port, in the process of serial port data receiving, the data is received one by one in the form of bytes, when a byte is received, the global time carries out assignment once on the last data receiving time, namely the global time and the data receiving time are considered to be synchronous in the process of the assignment, when the serial port has no data to receive or the data receiving is stopped, the global time is accumulated all the time, at a certain moment, the global time is certainly greater than the value of the last data receiving time, if the global time is greater than the last data receiving time, the data is no longer received at the moment, and the data receiving at the moment is considered to be finished;
step6, synchronizing RTC time in second level: therefore, the time gap is visually observed to be between 220ms and 230ms on an oscilloscope according to a time sequence diagram of data receiving displayed by the oscilloscope through experiments, if the time gap is subtracted from the last data receiving time by the global time and is smaller than 225ms at the moment and a pulse signal of 1pps exists at the current moment, the system time is rounded, so that the time correction is realized, and if the time gap is subtracted from the last data receiving time by the global time and is larger than or equal to 225ms, the next data receiving gap is waited.
2. The timing method for a 1pps pulse signal according to claim 1, wherein: the specific steps of Step1 are as follows: and searching a character corresponding to the next designated position by using a character string search function and a protocol $ GPGSA, A, checking the positioning condition for judging the positioning effect, if the corresponding character is less than 3, considering that the positioning precision is insufficient or the positioning is not successful, namely the GPS data is invalid, and if the corresponding character is more than or equal to 3, considering that the positioning is successful, namely the GPS data is valid.
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