GD32W51x User Manual
408
Verifying the RTC calibration
Calibration 1Hz output is provided to assist software to measure and verify the RTC precision.
Up to 2 RTC clock cycles measurement error may occur when measuring the RTC frequency
over a limited measurement period. To eliminate this measurement error the measurement
period should be the same as the calibration period.
When the calibration period is 32 seconds(this is default configuration)
Using exactly 32s period to measure the accuracy of the calibration 1Hz output can guarantee
the measure is within 0.477PPM (0.5 RTCCLK cycles over 32s)
When the calibration period is 16 seconds(by setting CWND16 bit)
In this configuration, CMSK[0] is fixed to 0 by hardware. Using exactly 16s period to measure
the accuracy of the calibration 1Hz output can guarantee the measure is within 0.954PPM
(0.5 RTCCLK cycles over 16s)
When the calibration period is 8 seconds(by setting CWND8 bit)
In this configuration, CMSK[1:0] is fixed to 0 by hardware. Using exactly 8s period to measure
the accuracy of the calibration 1Hz output can guarantee the measure is within 1.907PPM
(0.5 RTCCLK cycles over 8s)
Re-calibration on-the-fly
When the INITF bit is 0, software can update the value of RTC_HRFC using following steps:
1)
Wait the SCPF=0
2)
Write the new value into RTC_HRFC register
3)
After 3 ck_apre clocks, the new calibration settings take effect
16.3.13.
Time-stamp function
Time-stamp function is performed on RTC_TS pin and is enabled by control bit TSEN.
When a time-stamp event occurs on RTC_TS pin, the calendar value will be saved in time-
stamp registers (RTC_DTS/RTC_TTS/RTC_SSTS) and the time-stamp flag (TSF) is set to 1
by hardware. Time-stamp event can generate an interrupt if time-stamp interrupt enable (TSIE)
is set.
Time-stamp registers only record the calendar at the first time time-stamp event occurs which
means that time-stamp registers will not change when TSF=1.
To extend the time-stamp event source, one optional feature is provided: tamper function can
also be considered as time-stamp function if TPTS is set.
Note:
When the time-stamp event occurs, TSF is set 2 ck_apre cycles delay because of
synchronization mechanism.
Содержание GD32W515 Series
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Страница 389: ...GD32W51x User Manual 389 The FWDGT timeout can be more accurate by calibrating the IRC32K ...
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