Clock synchronisation in systems communication

Motive

in systems communications, timing is very important
just like when two people talk!
time synchronisation is the key when it comes to nodes in a network
how do we perceive/sense time naturally?

— Aswin (@akrv1) July 21, 2018

Starting with that, Guide to implementing a Clock synchronisation algorithm on low power wireless sensor networks.

following will be some pointers and papers to read before wandering in the wild to get things done and reinventing the wheel.

Literature survey

Message Time-stamping in Sensor Networks
Flooding time synchronisation protocol [1]
- this protocol is very good in terms of single of time synchronisation
- it uses linear regression, get ready to do some compute on your MCU
- very good numbers and explanation in those slides [2]
for multi-hop networks, this one is a good paper to read
- Optimal Clock Synchronization in Networks [3]
- Send fast synchronization pulses through the network to sync clock in networks
- pulseSync is the algorithm
Temperature Compensated Time Sync [4]
- The only requirement on that time synchronization protocol is that it can calculate the current frequency error with respect to the reference node’s clock. Unlike other time synchronization protocols, TCTS also records the current temperature during a synchronization exchange. Both the temperature and frequency error at the end of the synchronization exchange is cached in a frequency vs. temperature table in memory. [5]
- Before attempting subsequent resynchronization, TCTS will measure the current temperature and consults its internal calibration table. If the current frequency error for the measured temperature is cached, TCTS will not attempt to resynchronize with the reference node since a new time estimate is not required. Eventually, when all of the operating temperatures have been observed, TCTS will have auto-calibrated the low-stability clock, essentially providing a TCXO timebase. [5]
- In addition, since we know that the curve should fit a quadratic function of the form
  
  fe(T) = −A · (T − T₀)2 + B,
  
  where A is the temperature coefficient, T0 = 20◦C represents room temperature, and B is a frequency error offset, we can fit the measured calibration points to this curve and obtain frequency error estimates for previously unobserved temperatures, thus drastically improving the range and accuracy while eliminating a factory calibration step and allowing on-demand calibration. [5]
Virtual High-Resolution Time (VHT) [5]
- basic idea behind VHT
  - - During active periods, the high-frequency clock is turned on, and a hardware counter counts the number of high-frequency clock ticks that occur during each low-frequency clock interval, i.e., there are high-frequency clock ticks during each low-frequency one.
      
      φ₀ = f_L / f_H
    - At the time of the event, the system records not only the value of the counter sourced by the low-frequency clock but also the value of the counter sourced by the high-frequency clock which was reset at the end of the most recent clock tick of the low-frequency clock. Thus, this second timer will indicate the phase φ within a low-frequency clock tick, allowing an effective resolution to be up-sampled to the high-frequency clock (modulo one cycle of jitter). The event time is sampled as
      
      t_event=C_L ·φ₀ +φ.
    - While the high-frequency clock is not phase-locked with the low-frequency clock, the phase error is limited to < 1/f_H, and thus is of the same order as the quantization error.

Implementation of VHT in microcontrollers

The requirement is quite simple and the target chipset used in this project has additional two timers.

2 clocks driven by two oscillators
2 timers with capture and compare modes.

The Capture mode which will retrieve a timer value based on a signal event.

The Compare mode which will constantly monitor a timer counter value and compare it to a value set in the application. When they match, it will trigger an event.

Microchip developer help

The target implementation is on CC1350 chipset [6]. They have Four General-Purpose Timer Modules (Eight 16-Bit or Four 32-Bit Timers). With newest hardware revision CC1352r, almost same chip can be used to run Bluetooth 5.0. This has a M4 instead of a ARM M3 processor. This optimization with the increase in the memory footprint can be attributed to the new Bluetooth 5.0 standard.

The application framework used will be Contiki-OS [7]. I will use the latest version that is on development which also supports the SensorTag board and the launchpad [8]. A toolchain setup and compilation of the Contiki-OS is done in this post.

Illustration of the Virtual High-resolution Time event time-stamping mechanism on a micro- controller [5].

The two capture are connected to the event. The paper expects to make the interrupt for start of the frame delimited (SFD) which is previously justified for better resolution on clock synchronisation in figure 2 [5].

An additional capture unit on the fast timer captures the counter on every low frequency rising edge. As the Sync event, where the value of h₀ is stored in one of the capture units. Later, when the SFD line rises, the two capture units on the two timers store l₀ (the value of the low-frequency counter) and wh₁ (the value of the high frequency counter), respectively. Using these three captured values, the event time can be calculated as

t_event=l₀·φ₀+(h₁−h₀) modφ₀.

Counter overflows are an issue to be tackled. Overflows of the high-frequency counter are not a problem since they run only on a short burst when the system is synchronising / listening for packet. The low-frequency clock must have a counter width of 64-bit since 32-bit counters will overflow by 5 minutes since the low-frequency counters are used for long intervals.

As per the suggestion on [5] a 32KHz and 8MHz clocks are used for the timers. The MCU has Clock Speed up to 48-MHz.

References:

[1] http://www.isis.vanderbilt.edu/sites/default/files/Maroti_M_11_3_2004_The_Floodi.pdf

[2] https://www.tik.ee.ethz.ch/file/5562ed988ca095af8331114dd81c6c70/sensys09_slides.pdf

[3] https://people.mpi-inf.mpg.de/~clenzen/pubs/LSW09optimal.pdf

[4] https://ieeexplore.ieee.org/document/5170185/

[5] https://web.eecs.umich.edu/~prabal/pubs/papers/schmid10vht.pdf

[6] http://www.ti.com/lit/ds/symlink/cc1350.pdf

[7] http://contiki-ng.org/

[8] https://github.com/contiki-ng/contiki-ng/wiki/Platform-srf06-cc26xx

Compiling Contiki for CC1350

Setup:

macOS 10.13.5
VM – VirtualBox
Guest OS: Ubuntu 16.04

Setup Contiki on the local machine:

Install the following packages. you might need sudo right.

# sudo apt-get remove gcc-arm-none-eabi gdb-arm-none-eabi binutils-arm-none-eabi
# sudo add-apt-repository http://ppa:team-gcc-arm-embedded/ppa
# sudo apt-get update

Compile Contiki hello-world for Native:

Native means that your code will compile and run directly on your host PC.
for me, it will run on the Ubuntu 16.04 OS on the VM.

cd into your development folder.

# git clone https://github.com/contiki-os/contiki
# cd contiki/examples/hello-world
# make TARGET=native

mkdir obj_native
  CC        ../../core/ctk/ctk-conio.c
  CC        ../../platform/native/./contiki-main.c
  CC        ../../platform/native/./clock.c
  CC        ../../core/dev/leds.c
### output truncated ###
  AR        contiki-native.a
  CC        hello-world.c
  LD        hello-world.native
rm hello-world.co

The target command tells the compiler to compile for the current system.
This is what is later changed for cross compiling to our target platform.

Type the following command to run the hello-world program.

# ./hello-world.native
Contiki-3.x-3343-gbc2e445 started with IPV6, RPL
Rime started with address 1.2.3.4.5.6.7.8
MAC nullmac RDC nullrdc NETWORK sicslowpan
Tentative link-local IPv6 address fe80:0000:0000:0000:0302:0304:0506:0708
Hello, world

if this is how it worked! your compilation worked!

Compiling Contiki-OS for CC13xx

The only thing to be changed is the target. make clean is an important step.

make clean
make TARGET=srf06-cc26xx BOARD=sensortag/cc1350

this says the compilation works if you see the following:

CC ../../cpu/cc26xx-cc13xx/lib/cc13xxware/startup_files/ccfg.c
CC ../../cpu/cc26xx-cc13xx/./ieee-addr.c
AR contiki-srf06-cc26xx.a
CC ../../cpu/cc26xx-cc13xx/./fault-handlers.c
CC ../../cpu/cc26xx-cc13xx/lib/cc13xxware/startup_files/startup_gcc.c
CC hello-world.c
LD hello-world.elf
arm-none-eabi-objcopy -O ihex hello-world.elf hello-world.i16hex
srec_cat hello-world.i16hex -intel -o hello-world.hex -intel
arm-none-eabi-objcopy -O binary --gap-fill 0xff hello-world.elf hello-world.bin
cp hello-world.elf hello-world.srf06-cc26xx
rm hello-world.i16hex hello-world.co obj_srf06-cc26xx/fault-handlers.o obj_srf06-cc26xx/startup_gcc.o

This error absolutely means that the installation of the compiler for cross-compilation wasn’t successful.

/bin/sh: 1: arm-none-eabi-gcc: not found

Next step would be to compile with contiki-ng since, there is active development is happening there and to base all developments to that repo.

# git clone https://github.com/contiki-ng/contiki-ng
# cd contiki-ng
# git submodule update --init --recursive

navigate to the hello-world example and hit the following

# make clean make TARGET=srf06-cc26xx BOARD=sensortag/cc1350

References:

[1] https://sunmaysky.blogspot.com/2015/08/setup-6lbr-to-run-6lowpan-with-cc2531.html

[2]https://sunmaysky.blogspot.com/2015/09/contiki-subg-hz-6lowpan-on-cc1350.html

DNSed: A simple useable internet name for large scale IoT

Intent

When there is a city wide Wireless Sensor Network (WSN), this has to be resolved with anything meaningful, say name of where it is located. then this has to be the name that it should be resolved to.

to creat DNSed, as in past tense in English for DNS. To DNS the shit out of the IoT. To create an amazing network and to overload the DNS servers. To create everything out in the open, so everything in the Hollywood movies can come true.

Scenario

When a water tank level indicator at place called “Meereen”.
There is a number for the water tank which is 256.

then, this can be described in the internet nomenclature as

domain name: meereen.got
object: water tank
number: 256
sensor type: level indicator

this would translate to an internet name of “level.256.water.meereen.got”

usually, there is only a sensor in a an area and they are organised in cluster.

in that case, Meereen’s water tank is being referenced, and the sensor 256 is being addressed where the level is being asked for, https://256.water.meereen.got/level where level is a service provided by the sensor

Possibility:

It is possible to use BIND9 to build a DNS server, then create the zone records to point to the different sensors. the tutorial gives a good insight on deploying a BIND9 DNS server [3]. There are very good python libraries available in such an instance to build an DNS server and then work with their API. The following are some interesting DNS APIs for python to process DNS records on server.

[1] http://www.dnspython.org

[2] https://pypi.python.org/pypi/easyzone/1.2.1

Implementation:

In this effort, the implementation takes advantage of the REST API provided by DigitalOcean to make the DNS. as the idea is to create a very dynamic name resolution for IoT devices and this does not involve building a DNS server from scratch. The DNSed will be a library that will used in the IoT devices as well to communicate to the central server which will be further proxied to the DNS Server of DigitalOcean. This architecture would provide a method to have a better security by not distributing the API keys throughout the network on every device.

The functional block diagram below tries to describes this exact architecture

References:

[1] http://www.dnspython.org

[2] https://pypi.python.org/pypi/easyzone/1.2.1

[3] https://www.digitalocean.com/community/tutorials/how-to-configure-bind-as-a-private-network-dns-server-on-ubuntu-14-04

[4] https://developers.digitalocean.com/documentation/v2/#domain-records

[5]

SensyLight: sensible atmosphere using Internet of Things

The above video is from a research lab at the MIT Media Lab called Responsive Environments. They have a really interesting article [1] about a multimodal mediated work environment.

Internet of Things has been of great buzz these days. It is interesting, but why is it interesting? Just made a project/home lighting on this project.

So, here is the scenario for the internet of things. The thing in the Internet of Things is the web controlled lights – LED strip. The “control” part of the lights is managed by the Arduino. The task of Arduino would be to “GET” data that matters and send that info to the light strip. The ways in which the LED strip can be manipulated from the Arduino can be listed as

1 LED can have 3 inputs, R G B.
Each R G B can value from 0 – 255 which is 256 values.
There are 32 LEDs in the strip.

Which makes a lot of math and logical decisions for the Arduino to handle. That is the whole point of networking these devices, now they have access to on-demand computing resources. This means we need the medium to connect the Arduino to the internet. That is done using the WiFi module which communicates with the Arduino using USART communication.

There are two ways to handle the information flow:

To directly to give out RGB information an hour
- A lot of data transfer between the devices, but all of the computing, the decision is taken care of by the remote server
- the device is highly dependent on the connection for operation
To query the server for Sunlight information (sunrise and sunset) and compute the colour information.
- Having an update system to change the “compute” algorithm makes it highly robust.
- Gets information for a day / a week and then “compute” with the algorithm. Also, listen for any settings like
  - Party lights
  - Work lights
  - get back to sunlight operation

Tools used:

Hardware
- Arduino ATMega 2560
- WiFi module – ESP8266
  - Since the module isn’t compatible with the voltage operation, logic level shift adapter is added and interfaced with Arduino USART
- LED strip
Software
- Arduino IDE
  - Proposed library for ESP8266 – <https://github.com/itead/ITEADLIB_Arduino_ESP8266>
  - Library for the LED Strip <https://learn.adafruit.com/adafruit-neopixel-uberguide/arduino-library>
- Pycharm
  - for implementation of the web service using Flask
- API for sunrise/set cycle – openstreetmaps.org

Low cost, easy implementation of mediated atmospheres, to make your apartment to provide sensible lighting that can help harmonize the body and mind with the circadian rhythm.

[1] 17161.JosephA.Paradiso.Preprint1.pdf

[2] 192196471

Developing for ESP8266 using Arduino IDE

Cut to action steps:

Install Arduino IDE
Install board support packages to compile for ESP8266
1. ```
http://arduino.esp8266.com/stable/package_esp8266com_index.json
```
2. How and where to do it!
  1. first add that URL in the additional board managers URL
  2. now goto the board manager and look for ESP8266 and install the package
  3. compile your first program, don’t upload yet
  4. To upload, if you have NodeMCU, Arduino takes care of turning the boot-loader mode. if any other, then better to put it yourself into boot-loader mode.

Enjoy ESP8266 development!

Raspberry Pi NFC reader driver installation ACR122u

First add the following dependencies for the NFC driver and other modules

sudo apt-get install pcscd libusb-dev libpcsclite1 libpcsclite-dev dh-autoreconf

I also installed the drivers from the official website for my device.

it can be found here (disclaimer: I do not still not know if this step is required)

then install the python package with pip

sudo pip install nfcpy

now use the documentation http://nfcpy.readthedocs.io for using the nfc card with python. The python interface doesn’t use the LED notifications on the device, I have to find out how it works with the lights!

3 step procedure for installing raspian SD card image on Mac osX : CLI based

Yup, just like always open the terminal and put in the following to find the dev path of the SD card.

diskutil list

NO NAME with ID disk5 is what we will have to unmount

diskutil unmountDisk /dev/disk5

Now, copy the data to the SD card using the dd command on the terminal after to cd into the folder where you have downloaded the image. Usually its in the downloads folder when you do it with safari.
sudo dd bs=1m if=2015-05-05-raspbian-wheezy.img of=/dev/rdisk5

After sometime the terminal cursor blinks, it will look like the following image when it is successful. I didn’t come across the error from the actual source page, but when it does, look it up here -> Official Documentation (which is also my source)

as the title says, lets hit the raspberryPi with the new card and kick on with some electrons!

Testing Contiki-os with the first program using CC2530 / CC2531

This is not going to take too long for you to test your first Contiki program which will enable you to test your environment setup and also to understand the procedure of development using Contiki-os for the target chips CC2530 and CC2531. Continue reading “Testing Contiki-os with the first program using CC2530 / CC2531” →

TI CC2530DK – Contiki OS – Internet of Things

This blog post is an effort to create a one stop information for starting off your Contiki project with cc2530DK.

There is enough information already available on Github wiki. This post is more than an extension to have all information under one place and as usual my way of documenting my projects!

Continue reading “TI CC2530DK – Contiki OS – Internet of Things” →

All about Google WiFi Positioning System

WiFi Positioning system is a new way to get precise localisation. It is used in conjunction with GPS to achieve better accuracy. Read through to know how there is a slight privacy intrusion and how you can take care of your privacy issues. I am also sharing some interesting things about this WiFi Positioning System (WPS) that Google offers through its developer API.

It is interesting that Google asks for you to sign up for logging the access point (AP) information in your android phone. Well if you knew when and where it is asked, you will surely hit NO!

They collect your AP information mostly without clear notice and then you have to pay to use the API to access this information. Atleast this is what Google does.

Well some digging says it is just done periodically. My conclusions of how AP information tagged with location is logged are as follows

It is somewhere connected to location reporting from Google Location Services.
It could be just the localisation data that is sent to Google to while you are using your apps that require location.

So Google actually logs all the Access Point (AP) a device connects to and with the help of GPS it is geolocated and the info is tagged and sent to Google servers!

How to opt out of this WPS?