MAX-M10S - Integration manual
zero. Consequently, the information in GPS L1 message does not differentiate between, for example,
1980, 1999, or 2019. GPS L1 receivers must thus use additional methods to calculate the full week
number.
Although BeiDou and Galileo have similar representations of time, they still transmit sufficient
bits for the week number to be unambiguous for the foreseeable future (the first ambiguity will
be in 2078 for Galileo, and not until 2163 for BeiDou). GLONASS presents the time and date in
different way and transmits sufficient information to avoid any ambiguity during the expected
lifetime of the system (the first ambiguous date will be in 2124). Therefore, the receiver regards
the date information transmitted by GLONASS, BeiDou, and Galileo to be unambiguous and, where
necessary, uses this information to resolve any ambiguity in the GPS date.
If the receiver is connected to a simulator, be aware that GPS time is referenced to 6th
January 1980, GLONASS to 1st January 1996, Galileo to 22nd August 1999 and BeiDou to
1st January 2006; the receiver cannot be expected to work reliably with signals simulated
before these dates.
2.8.8.1 GPS-only date resolution
If only GPS L1C/A signals are available, the receiver establishes the date by assuming that all week
numbers must be at least as large as the reference rollover week number. The default value for
the reference rollover week number is selected at the compile time of the receiver firmware and is
normally set to a value of a few weeks before the software is completed. The value can be overridden
by CFG-NAVSPG-WKNROLLOVER configuration item.
The following example illustrates how this works:
Assume that the reference rollover week number set in the firmware at compile time is 2148 (which
corresponds to a week in calendar year 2021, but is transmitted by the satellites as 100). In this case,
if the receiver sees transmissions containing week numbers in the range of 100 ... 1023, they are
interpreted as week numbers 2148 ... 3071 (calendar years 2021 ... 2038), whereas transmissions
with week numbers from 0 to 99 are interpreted as week numbers 3072 ... 3171 (calendar years
2038 ... 2040).
It is important to set the reference rollover week number correctly when supplying the
receiver with simulated signals, especially when the scenarios are in the past.
2.9 Time mark
The receiver can be used to provide an accurate measurement of the time at which a pulse was
detected on the external interrupt pin. The reference time can be chosen by setting the time source
parameter to UTC, GPS, GLONASS, BeiDou, Galileo or local time in the CFG-TP-* configuration group.
The UTC standard can be set in the CFG-NAVSPG-* configuration group. The delay figures defined
with CFG-TP-* are also applied to the results output in the UBX-TIM-TM2 message.
A UBX-TIM-TM2 message is output at the next epoch if
• The UBX-TIM-TM2 message is enabled, and
• a rising or falling edge was triggered since last epoch on the EXTINT pin.
The UBX-TIM-TM2 messages includes the time of the last time mark, new rising/falling edge
indicator, time source, validity, number of marks and an accuracy estimate.
Only the last rising and falling edge detected between two epochs is reported since the
output rate of the UBX-TIM-TM2 message corresponds to the measurement rate configured
with CFG-RATE-MEAS (see
UBX-20053088 - R03
2 Receiver functionality
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