.. _nrf-clock-skew-sample:
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
******************************
.. zephyr-app-commands::
:zephyr-app: samples/boards/nrf/clock_skew
:board: nrf52dk_nrf52840
:goals: build flash
:compact:
Running:
Sample Output
=============
.. code-block:: console
*** 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
08f4ce4efb