1. Integrated Zephyr Connectivity
Presentation abstract:
Connectivity is the ‘I’ in IOT.     This talk will provide an overview of Zephyr communications enablers, their current state and future plans.   Insight on best practices, development and verification methods will also be given.  

2. Zephyr Connectivity: Current status
CoAP
DTLS
Bluetooth Smart API
UDP
Intel® Curie™ Module
Bluetooth
Driver
HCI host stack
IPv6
6LoWPAN
3-wire UART HCI
driver
5-wire UART HCI
driver
MAC (cc2520)
802.3
(Intel® Galileo™ 2 Ethernet transceiver)
When we speak about Connectivity for Zephyr, we are talking specifically about  the support for remote communication, both wired and wireless that is built into Zephyr kernel and supplied with the OS.
When we started the project, our goal was to add Bluetooth and IEEE (low rate wireless personal area networks) / 6LoWPAN support .
We chosen to implement HCI Bluetooth from scratch.
We took 15.4, 6LoWPAN and IP from Contiki
After developing Bluetooth APIs we decided to provide implementation for nRF51 controller which is part of Curie
We decided to start with nanokernel support so that our stacks can be used in the most resource constrained/nanokernel configurations
On the roadmap:
Bluetooth
Classic HCI stack, key enablers
Persistent storage
Broader support for Curie
IP stack:
TCP
MAC driver abstraction
More MAC drivers
6LoWPAN
IPSP router

3. Buffers in Zephyr Comms Stacks
struct net_buf
Analogous to Linux kernel sk_buff
Static (build-time) allocation
Free buffers managed through a FIFO
buf = net_buf_get(fifo);
Helpers for encoding & decoding
Optional protocol specific user-data
Reference counting & minimizing data copies
Introduction of common design of a protocol buffer was a key change comparing to Contiki stacks.
Buffers are the most resource consuming parts of the networking stack . We modelled them after sk_buf of Linux kernel
Buffers are directly compatible with Zephyr nano-fifo (have header pre-allocated in structure).
Buffer pools are configured at compile-time using macros. Buffers can be of different sizes.
In our case, the single structure across all networking stacks allowed us adapting 6LoWPAN for Bluetooth without much trouble
In the coming iterations we plan to work more on optimizing buffer usage across the entire system.

4. 6LoWPAN Task FIFO pair IPv6 Fiber FIFO pair Fiber
6LoWPAN - IPv6 over Low power Wireless Personal Area Networks.
Defines way of sending IPv6 over networks and Bluetooth Smart Connection-oriented Channels
link-local IPv6 addresses and stateless IPv6 address auto-configuration
Neighbor Discovery (RFC 6775)
Header Compression
IPSP: 6LoWPAN for Bluetooth
Adopted late 2014
Requires L2CAP Connection oriented Channels
Uses RFC 7668: IPv6 over Bluetooth Low Energy
Two roles
Node
Router
Task
Application
FIFO pair
IPv6
6LoWPAN
Fiber
FIFO pair
Bluetooth Smart
MAC
Fiber
Original 6LoWPAN implementation is from contiki.
What we have added:
- Provided a possibility to use two bearers (added Bluetooth bearer support)
Adapted to our network buffers
Fragmentation/reassembly is done only for 15.4; BLE takes care of it iself.

5. IP stack Rx fiber Global Rx FIFO for receiving
Task A
Rx fiber
Global Rx FIFO for receiving
array of network contexts (“sockets”)
Look up Tasks’ Rx FIFOs
Task
read: net_receive()
write: net_buf_get(), net_send()
Tx fiber
Global Tx FIFO for sending
Write to “driver’s” Tx FIFO
Task B
RX FIFO
TX FIFO
RX fiber
TX fiber
IP stack
Global RX FIFO
MAC driver
Major changes to the original ConTiki uIP stack
Re-entrant. No more global data usage. ( contiki used global buffers)
Adapted to net_buffer
We have a single TX FIFO and per-application RX FIFO. Allows multiple applications wait for their data

6. UDP Hello World data[] = “Hello world!”;
net_init(); /* Initialize network subsystem */
context = allocate_network_context(); /* Populate data structures */
tx_buffer = ip_buf_get_tx(context, data_length); /* Allocate TX buffer */
memcpy(get_data_pointer(tx_buffer), data, data_length); /* Fill TX buffer */
net_send(tx_buffer); /* Actually send the data */ …
rx_buffer = net_receive(context, WAIT_TICKS); /* Wait to get data from net */
if (rx_buffer) {
use_data(get_data(rx_buffer)); /* Make some use of the data */
ip_buf_unref(rx_buffer); /* Recycle the buffer */ }
A small example of sending udp and waiting for some response

7. Developing IP Application in QEMU
Develop Zephyr IP applications using host network adapter
Connect two VMs together
Use tunslip tool from ConTiki
Trace network traffic
IP stack
SLIP driver
Application
Zephyr/QEMU
/dev/net/tun0
Linux/Host
UART
tunslip6
Convenient BKM if you want to check IP-related behavior of your app and can be otherwise made QEMU-compatible
Using SLIP driver coming from ConTiki and tunslip6 tool . Can either connect Qemu VM to the external network using tun interface or connect two VMs together
Linux side: slip-tun -> tool from contiki creates tun interface and pumps the data across -> we get IPv6 from TUN device.
To get IP address SLAAC ( Stateless Autoconfiguration) is used and IPv6 address is generated from MAC address
For Linux host we assign ipv6 address manually

8. Bluetooth Smart HCI Host Stack
Bluetooth 4.2 compliant
GAP (Generic Access Profile)
Peripheral & Central
Observer & Broadcaster
GATT (Generic Attribute Profile)
Server to be a sensor
Client to access sensors
IPSP for IPv6 over Bluetooth Smart
Clean HCI driver abstraction
3-Wire (H:5) & 5-Wire (H:4) drivers available
drivers/bluetooth/ for drivers, net/bluetooth/ for stack
Verified with multiple popular controllers
Supporting both nano- & micro kernels  
Highly configurable
Features, buffer sizes/counts, etc
Bluetooth Smart API
HCI Core
HCI Driver
L2CAP
L2CAP CoC
ATT
SMP
IPSP/6LoWPAN
GATT
GAP
In the beginning we analyzed the available options for Bluetooth stack, found none and started from scratch.
Minimal footprint is around 30K (with XIP) [ 20 K code + 10 K RAM] . Very much configurable

9. Configuring Bluetooth Features
Select HCI driver
Features
GAP/GATT roles
Security (pairing & signing)
Define buffer sizes & counts
Number of paired devices
Number of connections
Enable debug options
Every Bluetooth-enabled application starts with configuring relevant features of the Bluetooth stack

10. Creating Bluetooth Smart Service
Initialize the stack
bt_init()
Register GATT service database
bt_gatt_register(array of attributes)
Advertise your presence & let others connect
bt_le_adv_start(parameters)
Notify of value changes
bt_gatt_notify(params)
Samples found under samples/bluetooth/*
One of the important roles we see for our OS/Bluetooth stack is to allow creation of smart bluetooth smart-connected sensors. Hence, this example of the GATT service [ =code running on the sensor]
This simple example requires no pairing, just connecting
Sample services, we have and/or will be made available are
– heart rate
-cadence (bicycle)
-temperature/environment profile

11. Developing for Bluetooth in QEMU
Develop Zephyr Bluetooth Application using host HCI adapter
Trace HCI commands
Linux host + qemu
BlueZ btproxy tool to forward local (host) adapter to qemu
Any type of local adapter supported (transport gets converted to H:4)
Linux-side HCI tracing (with btmon or hcidump)
Just a matter of “btproxy -u” & “make qemu”
HCI Host Stack
5-wire UART HCI
driver
Application
Zephyr/QEMU
Host Bluetooth Driver
Linux/Host
UART
btproxy
Allows using Zephyr stack with the Bluetooth hardware attached to the external host.
Might help to identify and solve problems specific to the Bluetooth adapter without resorting to on-device debugging.
All powerful tools of BlueZ can be used, tracing and dumping

12. Intel® Curie™ Bluetooth Smart Driver
Custom RPC protocol exposed by Nordic Semiconductor nRF51822 chip on Arduino 101/Curie ™
Available as a dedicated driver (drivers/nble) that implements the same API (include/bluetooth/*.h) as the HCI based stack
Subset of HCI stack features (only Bluetooth 4.0)

13. Summary
Integrated Zephyr connectivity allows to create Bluetooth Smart and 15.4-conncted applications in an open-source way
In the coming months, we plan to add TCP, IPv4, Bluetooth BR EDR functionality and number of other enhancements including Smart Mesh support
We warmly welcome both users of and contributors to our software!

14. Find Out More at Embedded World
Explore the Booth
Attend Booth Sessions
Demos showcasing technology, tools and 3rd party integration
Speak with Zephyr Project representatives
Meet with Linux Foundation to learn more about membership
Tuesday, Feb 23
Wednesday, Feb 24
Thursday, Feb 25
10:00am – 10:45am
Project Overview
10:30am – 11:45am
9:30am – 10:15am
11:00am – 11:45am
Tech Overview
1:30pm – 2:15pm
10:30am – 11:15am
3:00pm – 3:45pm
UbiquiOS
2:30pm – 3:15pm
4:00pm – 4:45pm
Comms Overview
3:30pm – 4:15pm
5:00pm – 5:45pm
Security
4:30pm – 5:15pm
1/12/2019