nRF5x Clock Skew Demo¶
Overview¶
This sample uses the API for correlating time sources to measure the skew between HFCLK (used for the CPU) and LFCLK (used for system time).
The CONFIG_APP_ENABLE_HFXO Kconfig option can be select to configure
the high frequency clock to use a crystal oscillator rather than the
default RC oscillator. (Capabilities like Bluetooth that require an
accurate high-frequency clock generally enable this source
automatically.) The relative error is significantly lower when HFXO is
enabled.
Requirements¶
This application uses any nRF51 DK or nRF52 DK board for the demo.
Building, Flashing and Running¶
west build -b nrf52dk_nrf52840 samples/boards/nrf/clock_skew
west flash
Running:
Sample Output¶
*** Booting Zephyr OS build zephyr-v2.4.0-693-g4a3275faf567 ***
Power-up clocks: LFCLK[ON]: Running LFXO ; HFCLK[OFF]: Running HFINT
Start TIMER_0: 0
Timer-running clocks: LFCLK[ON]: Running LFXO ; HFCLK[OFF]: Running HFINT
Checking TIMER_0 at 16000000 Hz against ticks at 32768 Hz
Timer wraps every 268 s
Ty Latest Base Span Err
HF 00:00:00.015667
LF 00:00:00.404296
Started sync: 0
Ty Latest Base Span Err
HF 00:00:10.001151 00:00:00.015667 00:00:09.985483
LF 00:00:10.413818 00:00:00.404296 00:00:10.009521 00:00:00.024038
Skew 0.997599 ; err 2401411 ppb
Ty Latest Base Span Err
HF 00:00:19.997456 00:00:00.015667 00:00:19.981788
LF 00:00:20.434265 00:00:00.404296 00:00:20.029968 00:00:00.048180
Skew 0.997595 ; err 2405464 ppb
Ty Latest Base Span Err
HF 00:00:29.993845 00:00:00.015667 00:00:29.978178
LF 00:00:30.454650 00:00:00.404296 00:00:30.050354 00:00:00.072176
Skew 0.997598 ; err 2401828 ppb
Ty Latest Base Span Err
HF 00:00:39.986181 00:00:00.015667 00:00:39.970514
LF 00:00:40.475036 00:00:00.404296 00:00:40.070739 00:00:00.100225
Skew 0.997499 ; err 2501189 ppb
Ty Latest Base Span Err
HF 00:00:49.981516 00:00:00.015667 00:00:49.965848
LF 00:00:50.495422 00:00:00.404296 00:00:50.091125 00:00:00.125277
Skew 0.997499 ; err 2501010 ppb
Ty Latest Base Span Err
HF 00:00:59.976042 00:00:00.015667 00:00:59.960375
LF 00:01:00.515808 00:00:00.404296 00:01:00.111511 00:00:00.151136
Skew 0.997486 ; err 2514243 ppb
...
Ty Latest Base Span Err
HF 00:01:59.935661 00:00:00.015667 00:01:59.919994
LF 00:02:00.638153 00:00:00.404296 00:02:00.233856 00:00:00.313862
Skew 0.997390 ; err 2610445 ppb
...
Ty Latest Base Span Err
HF 00:04:59.769166 00:00:00.015667 00:04:59.753498
LF 00:05:01.005279 00:00:00.404296 00:05:00.600982 00:00:00.847484
Skew 0.997181 ; err 2819240 ppb
...
Ty Latest Base Span Err
HF 00:09:59.513787 00:00:00.015667 00:09:59.498119
LF 00:10:01.617156 00:00:00.404296 00:10:01.212860 00:00:01.714741
Skew 0.997148 ; err 2852201 ppb
...
Ty Latest Base Span Err
HF 00:30:08.384536 00:00:00.015667 00:30:08.368868
LF 00:30:14.084594 00:00:00.404296 00:30:13.680297 00:00:05.311429
Skew 0.997072 ; err 2928495 ppb
...
Ty Latest Base Span Err
HF 00:59:57.353602 00:00:00.015667 00:59:57.337934
LF 01:00:07.734375 00:00:00.404296 01:00:07.330078 00:00:09.992144
Skew 0.997230 ; err 2770006 ppb
...
Ty Latest Base Span Err
HF 02:59:33.181323 00:00:00.015667 02:59:33.165656
LF 03:00:03.434265 00:00:00.404296 03:00:03.029968 00:00:29.864312
Skew 0.997236 ; err 2764463 ppb
...
Ty Latest Base Span Err
HF 05:59:55.031709 00:00:00.015667 05:59:55.016042
LF 06:00:57.120941 00:00:00.404296 06:00:56.716644 00:01:01.700602
Skew 0.997151 ; err 2849042 ppb