ANT: Background Scanning

The ANT Background Scanning Example shows how to implement a background scanning channel in combination with a master channel on a single device. It also demonstrates how to use extended messages to obtain Received Signal Strength Indication (RSSI) and channel ID information from received packets.

Overview

On dual core, this sample uses sysbuild to add a network core image to the build by defining the ‘’NRF_DEFAULT_ANT_ONLY’’ with a default value of ‘’y’’ in Kconfig.sysbuild.

Description

Background scanning channels in ANT are searching channels that never synchronize with a master. Instead of acquiring a master, ANT will pass the data to the master and continue searching. These channels allow for asynchronous topologies with other channels running independently on the same device.

This example uses two channels: one background scanning channel that can receive data from multiple devices and one master channel. The master channel in this example copies the received RSSI and channel ID information and mirrors these parameters back to the transmitting devices.

After startup or reset, the ANT node opens one background scanning channel and one master channel. The background scanning channel is configured similar to a regular slave channel, but with a special flag set to denote its function. The search time-out is set to infinity to ensure that the background scanning channel continues searching for other channels.

Channel configuration

This example uses the following channel configurations:

Parameter

Beacon Channel

Background Scanning Channel

Channel type

Master (0x10)

Slave (0x00)

Extended assignment

N/A

EXT_PARAM_ALWAYS_SEARCH (0x01)

Network key

Public

Public

RF channel

77 (2477 MHz)

77 (2477 MHz)

Device number

0x02

0x00 (wild card)

Device type

0x01

0x01

Transmission type

0x05

0x05

Channel period

2048 (16 Hz)

N/A

Search time-out (high priority)

N/A

0x00 (No HP search)

Search time-out (low priority

N/A

0xFF (Infinite)

Message format

The master channel on each device sends a single payload of data. This payload indicates the signal strength and the channel ID of the last message that was received on the background scanning channel.

The following table shows the message format of the default master message:

Byte

Description

0

Page number = 1 (ANT_BEACON_PAGE)

1

RSSI value (signed dBm value, corresponding to the device number)

2-3

Device number of the last message that was received on the background scanning channel (little endian, corresponding to the RSSI value)

4-5

Reserved

6

Counter that increases with each channel period

7

Number of messages that were received on the background scanning channel

Requirements

Hardware platforms

PCA

Board name

Build target

nRF5340 DK

PCA10095

nrf5340dk/nrf5340

nrf5340dk/nrf5340/cpuapp

nRF52840 DK

PCA10056

nrf52840dk/nrf52840

nrf52840dk/nrf52840

Configuration

This sample configuration is split into the following two files:

  • generic configuration is available in the prj.conf file (single core, or dual core cpuapp)

  • configuration for the ant_rpc network core image is stored in the sysbuild/ant_rpc subdirectory (dual core cpunet)

Building and running

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

Testing using two boards

  1. Connect to the application core virtual COM port of both of the nRF DK for logging output using a serial terminal (PuTTy, Tera Term).

  2. Compile and program atleast 2 boards.

  3. Observe that the boards occasionally print basic information about the sender of the message.

Testing using ANTware II

After programming the sample to your development kit, you can test the Background Scanner using ANTware II:

  1. Compile and program the Background Scanner.

  2. Run ANTware II. Select your ANT PC dongle (for example, ANTUSB-m) from the available devices.

  3. Configure the device by loading the device profile configuration from the following file:

    ant\samples\ant_broadcast_rx\ant_background_scanning_test.xml

    Alternatively, you can configure the device channels manually:

    Channel 0: Set the channel assignment to Master. Set the channel ID to “1, 1, 5”. Set the channel period to 2048. Set the RF frequency to 77.

    Channel 1: Set the channel assignment to Slave. Set the channel ID to “0, 1, 5”. Set the channel period to 2048. Set the RF frequency to 77.

  4. Click the Auto-Open button on both channels. Check the application core virtual COM port of the nRF DK for logging output.

    [00:00:02.459,930] <inf> ant_background_scanning: ANT Background Scanning example started.
[00:00:15.726,043] <inf> ant_background_scanning: =============================================================
[00:00:15.726,074] <inf> ant_background_scanning: Message number 0
[00:00:15.726,074] <inf> ant_background_scanning: Device ID:     1
[00:00:15.726,104] <inf> ant_background_scanning: RSSI:          196
[00:00:15.851,043] <inf> ant_background_scanning: =============================================================
[00:00:15.851,074] <inf> ant_background_scanning: Message number 1
[00:00:15.851,074] <inf> ant_background_scanning: Device ID:     1
[00:00:15.851,104] <inf> ant_background_scanning: RSSI:          195
[00:00:17.288,574] <inf> ant_background_scanning: =============================================================
[00:00:17.288,604] <inf> ant_background_scanning: Message number 2
[00:00:17.288,604] <inf> ant_background_scanning: Device ID:     1
[00:00:17.288,604] <inf> ant_background_scanning: RSSI:          196
[00:00:17.413,574] <inf> ant_background_scanning: =============================================================
[00:00:17.413,574] <inf> ant_background_scanning: Message number 3
[00:00:17.413,604] <inf> ant_background_scanning: Device ID:     1
[00:00:17.413,604] <inf> ant_background_scanning: RSSI:          197

  5. You can also check the message payload that is received on the slave channel. The reported device number (byte 2 and 3) is the channel ID that you configured for the master channel. The reported RSSI value (byte 1) changes when the board is moved closer or further away from the ANT USB dongle. For example

    Payload

    Description

    Received BROADCAST_DATA_0x4E :: 4e, 00-01-B6-32-00-00-00-8D-74

    Device number = 50

    Received BROADCAST_DATA_0x4E :: 4e, 00-01-B6-32-00-00-00-8E-74

    RSSI = -74 dBm (further away)

    Received BROADCAST_DATA_0x4E :: 4e, 00-01-CB-32-00-00-00-8A-0

    RSSI = -53 dBm (closer)