Kernel configuration

The Ubuntu Core officially supports Linux kernel version 4.4 therefore any new IoT device that is Ubuntu Core based should consider using it if possible. Moreover this is a long term supported kernel by the Linux kernel community.

Also, you could use an older version of the Linux kernel. Keep in mind however that some features might not be available. For example you need at least Linux kernel v3.13 to have the Bluetooth Low Energy functioning.

Using an older kernel yet having good interoperability will most probably require you to backport the Bluetooth part of the kernel from the newer release. This can be easily done using Kernel Backports Project

In short:

KERNEL VERSION	SUPPORT STATUS
>= 4.4	Will work out of the box
>= 3.13	Ok for Bluetooth Classic and LE however consider backporting
>= 3.10	Ok for Bluetooth Classic however consider backporting

The heart of Ubuntu Core is snapd which has some constraints on the kernel version used. In particular it requires the newest AppArmor patches. Therefore, when choosing a kernel please take a look at sample kernels that have all the bits necessary for snapd to run included. Also make sure to read the Board enablement overview.

Configuration

Note that the default Linux kernel for Ubuntu Core has al the necessary bits enabled by default.

Most of the Bluetooth systems will support Classic mode therefore you need to make sure that the following options are selected.

  [*] Networking support
      <M> Bluetooth subsystem support
        [*]   Bluetooth Classic (BR/EDR) features
    <M>     RFCOMM protocol support
    [*]       RFCOMM TTY support
    <M>     BNEP protocol support
    [*]       Multicast filter
    [*]       Protocol filter support
    <M>     CMTP protocol support
    <M>     HIDP protocol support
    [*]     Bluetooth High Speed (HS) features
    [*]   Bluetooth Low Energy (LE) features
    <M>     Bluetooth 6LoWPAN support
    [ ]   Bluetooth self testing support
    [*]   Export Bluetooth internals in debugf

Note that this is a general set and it might be further tweaked to match your device use-cases and capabilities. For example, on devices that will not offer networking over Bluetooth, a BNEP can be disabled.

Note that if your Bluetooth controller (chip) supports Bluetooth Low Energy, then leave the BLE related options selected or disable otherwise:

  [*] Networking support
      <M> Bluetooth subsystem support
    [*]   Bluetooth Low Energy (LE) features
    <M>     Bluetooth 6LoWPAN support

It is also important to remember about the UHID driver. It is needed for Bluetooth Low Energy (a.k.a. Smart) keyboards and mice.

Device Drivers
  HID support
    {M} HID bus support
    [*]   Battery level reporting for HID devices
    [*]   /dev/hidraw raw HID device support
    <M>   User-space I/O driver support for HID subsystem
    <M>   Generic HID driver 

Below are the Linux kernel config options for reference. They are based on the Linux core16 4.4.0-1040-raspi2 kernel which is the official Ubuntu Core Linux kernel for Raspberry Pi 2/3.

CONFIG_NET=y
CONFIG_BT=m
CONFIG_BT_BREDR=y
CONFIG_BT_RFCOMM=m
CONFIG_BT_RFCOMM_TTY=y
CONFIG_BT_BNEP=m
CONFIG_BT_BNEP_MC_FILTER=y
CONFIG_BT_BNEP_PROTO_FILTER=y
CONFIG_BT_CMTP=m
CONFIG_BT_HIDP=m
CONFIG_BT_HS=y
CONFIG_BT_LE=y
CONFIG_BT_6LOWPAN=m
CONFIG_BT_DEBUGFS=y

CONFIG_BT_HCIBCM203X=m
CONFIG_BT_HCIBFUSB=m
CONFIG_BT_HCIBPA10X=m
CONFIG_BT_HCIBTSDIO=m
CONFIG_BT_HCIBTUSB=m
CONFIG_BT_HCIBTUSB_BCM=y
CONFIG_BT_HCIBTUSB_RTL=y
CONFIG_BT_HCIUART=m
CONFIG_BT_HCIUART_3WIRE=y
CONFIG_BT_HCIUART_ATH3K=y
CONFIG_BT_HCIUART_BCM=y
CONFIG_BT_HCIUART_BCSP=y
CONFIG_BT_HCIUART_H4=y
CONFIG_BT_HCIUART_INTEL=y
CONFIG_BT_HCIUART_LL=y
CONFIG_BT_HCIUART_QCA=y
CONFIG_BT_HCIVHCI=m

CONFIG_BT_ATH3K=m
CONFIG_BT_BCM=m
CONFIG_BT_INTEL=m
CONFIG_BT_MRVL=m
CONFIG_BT_MRVL_SDIO=m
CONFIG_BT_QCA=m
CONFIG_BT_RTL=m
CONFIG_BT_WILINK=m