nRF CircuitPython boards will now provide the file transfer
service defined here: https://github.com/adafruit/Adafruit_CircuitPython_BLE_File_Transfer
USB capable boards will only advertise if previously bonded to a
device or if the reset button is pressed during the fast blue
flashes on start up. When pressed, the board will restart again but
the blue period will not flash.
Boards without USB will always advertise.
When previously bonded, the advertisement is private so that no
other peers can connect. If advertising publicly, the tx power is
lowered to reduce the likelihood of bonding from a distance.
This PR also fixes issues with loading identities of bonded peers
so that our address can now be resolved and we can resolve others'
addresses when scanning.
This is handy for remote characteristics because it allows for
the PacketBuffer binding code to have the correct max size. This
PR also adds checks so we don't write outside the outgoing buffer.
PacketBuffer facilitates packet oriented BLE protocols such as BLE
MIDI and the Apple Media Service.
This also adds PHY, MTU and connection event extension negotiation
to speed up data transfer when possible.
This PR refines the _bleio API. It was originally motivated by
the addition of a new CircuitPython service that enables reading
and modifying files on the device. Moving the BLE lifecycle outside
of the VM motivated a number of changes to remove heap allocations
in some APIs.
It also motivated unifying connection initiation to the Adapter class
rather than the Central and Peripheral classes which have been removed.
Adapter now handles the GAP portion of BLE including advertising, which
has moved but is largely unchanged, and scanning, which has been enhanced
to return an iterator of filtered results.
Once a connection is created (either by us (aka Central) or a remote
device (aka Peripheral)) it is represented by a new Connection class.
This class knows the current connection state and can discover and
instantiate remote Services along with their Characteristics and
Descriptors.
Relates to #586
