nRF9160: GNSS

This sample demonstrates how to use the GNSS interface to control the GNSS module. It also shows how to improve fix speed and accuracy with the nRF Cloud A-GPS library and how to use the nRF Cloud P-GPS library. Assistance data is downloaded from nRF Cloud using nRF Cloud’s REST-based device API.

Requirements

The sample supports the following development kit:

Hardware platforms

PCA

Board name

Build target

nRF9160 DK

PCA10090

nrf9160dk_nrf9160

nrf9160dk_nrf9160_ns

The sample is configured to compile and run as a non-secure application on nRF91’s Cortex-M33. Therefore, it automatically includes the Secure Partition Manager that prepares the required peripherals to be available for the application.

You can also configure it to use TF-M instead of Secure Partition Manager.

Overview

The sample first initializes the GNSS module. Then it handles events from the interface, reads the associated data and outputs information to the console. Because NMEA data needs to be read as soon as an NMEA event is received, a Zephyr message queue is used for buffering the NMEA strings. The event handler function reads the received NMEA strings and puts those into the message queue. The consumer loop reads from the queue and outputs the strings to the console.

Operation modes

The sample supports different operation modes:

  • Continuous

  • Periodic

  • Time-to-first-fix (TTFF) test

By default, the sample runs in continuous tracking mode. In continuous mode, GNSS tries to acquire a fix once a second.

In periodic mode, fixes are acquired periodically with the set interval.

In TTFF test mode, the sample acquires fixes periodically and calculates the TTFF for each fix. You can use the TTFF test mode without assistance or with any supported assistance method. You can also configure it to perform cold starts, where the stored data is deleted from GNSS before each start. If you enable assistance with cold starts, new assistance data is also downloaded and injected to GNSS before each start.

Output modes

The sample supports two output modes:

  • Position, Velocity, and Time (PVT) and NMEA

  • NMEA-only

By default, the sample displays information from both PVT and NMEA strings. You can also configure the sample to run in NMEA-only output mode, where only the NMEA strings are displayed in the console. In the NMEA-only output mode, you can visualize the data from the GNSS using a third-party tool.

A-GPS and P-GPS

When support for A-GPS or P-GPS, or both, is enabled, a Zephyr workqueue is used for downloading the assistance data. Downloading the data can take some time. The workqueue ensures that the main thread is not blocked during the operation.

When assistance support is enabled, the sample receives an A-GPS data request notification from the GNSS module, and it starts downloading the assistance data requested by the GNSS module. The sample then displays the information in the terminal about the download process. Finally, after the download completes, the sample switches back to the previous display mode.

Minimal assistance

GNSS satellite acquisition can also be assisted by providing factory almanac, GPS time, and coarse location to the GNSS module. Using this information, GNSS can calculate which satellites it should search for and what are the expected Doppler frequencies.

The sample includes a factory almanac that is written to the file system when the sample starts. The date for the factory almanac generation is in the factory_almanac.h file. The almanac gets inaccurate with time and should be updated occasionally. GNSS can use an almanac until it is two years old, but generally it should be updated every few months.

Configuration

See Configuring your application for information about how to permanently or temporarily change the configuration.

Configuration options

Check and configure the following Kconfig options for the sample:

CONFIG_GNSS_SAMPLE_NMEA_ONLY - To enable NMEA-only output mode

The NMEA-only output mode can be used for example with 3rd party tools to visualize the GNSS output.

CONFIG_GNSS_SAMPLE_ANTENNA_EXTERNAL - To use an external GNSS antenna

This configuration option should be enabled if an external GNSS antenna is used, so that the Low Noise Amplifier (LNA) can be configured accordingly.

CONFIG_GNSS_SAMPLE_ASSISTANCE_NRF_CLOUD - To use nRF Cloud A-GPS

This configuration option enables A-GPS usage.

CONFIG_GNSS_SAMPLE_ASSISTANCE_MINIMAL - To use minimal assistance

This configuration option enables assistance with factory almanac, time and location.

CONFIG_GNSS_SAMPLE_MODE_PERIODIC - To enable periodic fixes

This configuration option enables periodic fixes instead of continuous tracking.

CONFIG_GNSS_SAMPLE_PERIODIC_INTERVAL - To set interval (in seconds) for periodic fixes

This configuration option sets the desired fix interval.

CONFIG_GNSS_SAMPLE_PERIODIC_TIMEOUT - To set desired timeout (in seconds) for periodic fixes

This configuration option sets the desired timeout for periodic fixes.

CONFIG_GNSS_SAMPLE_MODE_TTFF_TEST - To enable time-to-first-fix (TTFF) test mode

This configuration enables the TTFF test mode instead of continuous tracking. When TTFF test mode is enabled, the CONFIG_GNSS_SAMPLE_NMEA_ONLY option is automatically selected.

CONFIG_GNSS_SAMPLE_MODE_TTFF_TEST_INTERVAL - To set the time between fixes in TTFF test mode

This configuration option sets the time between fixes in TTFF test mode.

CONFIG_GNSS_SAMPLE_MODE_TTFF_TEST_COLD_START - To perform cold starts in TTFF test mode

This configuration option makes the sample perform GNSS cold starts instead of hot starts in TTFF test mode. When assistance is used, LTE may block the GNSS operation and increase the time needed to get a fix.

CONFIG_GNSS_SAMPLE_LTE_ON_DEMAND - To disable LTE after assistance download

When using assistance, LTE may block the GNSS operation and increase the time needed to get a fix. This configuration option disables LTE after the assistance data has been downloaded, so that GNSS can run without interruptions.

Building and running

This sample can be found under samples/nrf9160/gnss in the nRF Connect SDK folder structure.

The sample is built as a non-secure firmware image for the nrf9160dk_nrf9160_ns build target. Because of this, it automatically includes the Secure Partition Manager. You can also configure it to use TF-M instead of SPM.

See Building and programming an application for information about how to build and program the application.

If the sample is to be used with the SUPL client library, the library must be downloaded and enabled in the sample configuration. You can download it from the Nordic Semiconductor website. See SUPL client and SUPL client OS integration for information on installing and enabling the SUPL client library.

Testing

After programming the sample and all the prerequisites to the development kit, test it by performing the following steps:

  1. Connect your nRF9160 DK to the PC using a USB cable and power on or reset your nRF9160 DK.

  2. Open a terminal emulator.

  3. Test the sample by performing the following steps:

    If the default output mode is enabled:

    1. Observe that the following information is displayed in the terminal emulator:

      Tracking:  0 Using:  0 Unhealthy: 0
-----------------------------------
Seconds since last fix: 1
Searching [-]

NMEA strings:

$GPGGA,000000.00,,,,,0,,99.99,,M,0,,*37
$GPGLL,,,,,000000.00,V,A*45
$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99,1*2D
$GPGSV,1,1,0,,,,,,,,,,,,,,,,,1*54
$GPRMC,000000.00,V,,,,,,,060180,,,N,V*08
---------------------------------

    2. Observe that the numbers associated with the displayed parameters Tracking and Using change.

    3. Observe that the sample displays the following information upon acquiring a fix:

      Tracking:  7 Using:  5 Unhealthy: 0
-----------------------------------
Latitude:       61.491275
Longitude:      23.771611
Altitude:       116.3 m
Accuracy:       4.2 m
Speed:          0.0 m/s
Speed accuracy: 0.8 m/s
Heading:        0.0 deg
Date:           2020-03-06
Time (UTC):     05:48:24
PDOP:           3.1
HDOP:           2.1
VDOP:           2.3
TDOP:           1.8

NMEA strings:

$GPGGA,054824.58,6129.28608,N,02346.17887,E,1,07,2.05,116.27,M,0,,*22
$GPGLL,6129.28608,N,02346.17887,E,054824.58,A,A*6B
$GPGSA,A,3,10,12,17,24,28,,,,,,,,3.05,2.05,2.25,1*13
$GPGSV,2,1,7,17,50,083,41,24,68,250,38,10,14,294,46,28,23,071,38,1*56
$GPGSV,2,2,7,12,29,240,36,19,00,000,32,1,00,000,33,1*50
$GPRMC,054824.58,A,6129.28608,N,02346.17887,E,0.08,0.00,030620,,,A,V*29
---------------------------------

    If NMEA-only output mode is enabled:

    1. Observe that the following information is displayed in the terminal emulator:

      $GPGGA,000000.00,,,,,0,,99.99,,M,0,,*37
$GPGLL,,,,,000000.00,V,A*45
$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99,1*2D
$GPGSV,1,1,0,,,,,,,,,,,,,,,,,1*54
$GPRMC,000000.00,V,,,,,,,060180,,,N,V*08
$GPGGA,000001.00,,,,,0,02,99.99,,M,0,,*34
$GPGLL,,,,,000001.00,V,A*44
$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99,1*2D
$GPGSV,1,1,2,17,,,24,1,,,28,1*6D
$GPRMC,000001.00,V,,,,,,,060180,,,N,V*09
$GPGGA,000002.00,,,,,0,02,99.99,,M,0,,*37
$GPGLL,,,,,000002.00,V,A*47
$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99,1*2D
$GPGSV,1,1,2,17,,,24,1,,,28,1*6D
$GPRMC,000002.00,V,,,,,,,060180,,,N,V*0A

    If TTFF test mode is enabled:

    1. Observe that the following information is displayed in the terminal emulator:

      $GPGGA,000033.00,,,,,0,,99.99,,M,,M,,*66
$GPGLL,,,,,000033.00,V,N*4A
$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99,1*2D
$GPGSV,3,1,10,1,,,36,5,,,26,7,,,25,10,,,44,1*53
$GPGSV,3,2,10,14,,,43,17,,,37,21,,,41,23,,,43,1*64
$GPGSV,3,3,10,24,,,31,28,,,39,1*61
$GPRMC,000033.00,V,,,,,,,060180,,,N,V*08
$GPGGA,121300.68,6129.28608,N,02346.17887,E,1,05,2.41,123.44,M,,M,,*7A
$GPGLL,6129.28608,N,02346.17887,E,121300.68,A,A*63
$GPGSA,A,3,01,10,17,21,23,,,,,,,,6.32,2.41,5.84,1*12
$GPGSV,4,1,14,1,17,047,37,7,-22,107,25,10,22,314,44,12,09,232,,1*41
$GPGSV,4,2,14,13,29,173,,14,38,072,44,15,40,211,,17,46,106,37,1*65
$GPGSV,4,3,14,19,35,139,,21,15,019,41,23,19,279,42,24,51,273,32,1*6F
$GPGSV,4,4,14,28,,,39,30,00,110,,1*52
$GPRMC,121300.68,A,6129.28608,N,02346.17887,E,0.10,0.00,200122,,,A,V*2C
[00:00:34.790,649] <inf> gnss_sample: Time to fix: 34
[00:00:34.796,447] <inf> gnss_sample: Sleeping for 120 seconds
[00:02:34.699,493] <inf> gnss_sample: Starting GNSS
$GPGGA,121500.82,,,,,0,,99.99,,M,,M,,*6B
$GPGLL,,,,,121500.82,V,N*47
$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99,1*2D
$GPGSV,1,1,0,,,,,,,,,,,,,,,,,1*54
$GPRMC,121500.82,V,,,,,,,200122,,,N,V*09
$GPGGA,121501.82,6129.28608,N,02346.17887,E,1,04,2.73,118.22,M,,M,,*78
$GPGLL,6129.28608,N,02346.17887,E,121501.82,A,A*69
$GPGSA,A,3,10,17,21,23,,,,,,,,,7.59,2.73,7.08,1*18
$GPGSV,4,1,13,1,18,046,28,10,22,313,49,12,10,232,26,13,28,173,25,1*51
$GPGSV,4,2,13,14,37,072,50,15,40,211,25,17,46,105,45,19,35,138,31,1*63
$GPGSV,4,3,13,21,15,018,45,23,18,278,45,24,52,273,,28,,,44,1*57
$GPGSV,4,4,13,30,00,110,,1*55
$GPRMC,121501.82,A,6129.28608,N,02346.17887,E,0.16,0.00,200122,,,A,V*20
[00:02:35.940,582] <inf> gnss_sample: Time to fix: 1
[00:02:35.946,319] <inf> gnss_sample: Sleeping for 120 seconds

    2. Observe that the samples displays the time to fix for each fix.

    If A-GPS and/or P-GPS support is enabled:

    1. Observe that the following message is displayed in the terminal emulator immediately after the device boots:

      [00:00:04.488,494] <inf> gnss_sample: Assistance data needed, ephe 0xffffffff, alm 0xffffffff, flags 0x3b

    2. Observe the following actions in the terminal emulator:

      1. The sample downloads the requested assistance data if needed (with P-GPS, the data may already be available in the flash memory).

      2. The sample continues after the download has completed.

Dependencies

This sample uses the following nRF Connect SDK libraries:

It uses the following sdk-nrfxlib library:

It uses the following Zephyr library: