About extended advertising

Extended advertising allows for much more capability and flexibility.

Allows for 251 bytes of advertisement data and up to 1650 bytes when chained (configuration dependant) vs 31.
New PHY's (physical layers) that allow for faster data rate (2M PHY) or long range/slower data rates (CODED PHY) as well as the original 1M PHY.
New periodic advertising, allowing the scanning device to sync with the advertisements of a beacon. This allows for the scanning device to sleep or perform other tasks before the next expected advertisement is sent, preserving cpu cycles and power (To be implemented).

Enabling extended advertising

Extended advertising is supported when enabled with the config option CONFIG_BT_NIMBLE_EXT_ADV set to a value of 1. This is done in menuconfig under Component config > Bluetooth > NimBLE options > Enable extended advertising, or set in nimconfig.h for Arduino, or in build_flags in PlatformIO.

When enabled the following will occur:

NimBLEScan::start method will scan on both the 1M PHY and the coded PHY standards automatically.
NimBLEClient::connect will use the primary PHY the device is listening on, unless specified (see below).
NimBLEClient::setConnectPhy becomes available to specify the PHY's to connect with (default is all).
NimBLEAdvertising is no longer available for use and is replaced by NimBLEExtAdvertising. NimBLEDevice::getAdvertising will now return an instance of NimBLEExtAdvertising.
NimBLEAdvertisementData is no longer available for use and is replaced by NimBLEExtAdvertisement. This new class is where everything about the advertisement is configured, including the advertisement intervals and advertisement ended callback.