A talk about Lora

Lora & LoraWan: 

Lora is actually a unique proprietary modulation format (phi layer). Semtech is the owner of the Lora RF technology and they give licenses to others.

LoraWan (MAC layer ) is an open standard maintained by Lora Alliance

RF basics of Lora : 

• A Lora Signal starts with a preamble signal & has a constant ramp chirp inside.
• The number symbols in a preamble signal = number of chirps/number of peaks of the ramp signal. 
• Lora has the ability to demodulate several orthogonal/simultaneous signals at the same time. this function is implemented in the gateway chips like SX1301 where all the nodes connect.
• LoRa RF physical layer uses a form of spread spectrum modulation.
• To maximize battery lifetime or to maximize signal transmission distance the transmission power level used in the Lora chip can be decreased or increased.  
• The communication between different end-devices and gateways can be on several different frequency channels and they can use different data rates.
• The use of the chirp spread spectrum technology enables communications with different data rates not to interfere with each other. In this way, a set of "virtual" channels can be created which increases the capacity of the gateway.

Signal-Detection

Signal Demodulate

Frequency and bandwidth: 

The LoRa wireless system makes use of the unlicensed frequencies that are available worldwide. The most widely used frequencies/bands are:

• 868 MHz for Europe
• 915 MHz for North America
• 433 MHz band for Asia

Basically operating at lower frequencies than those of the 2.4 or 5.8 GHz ISM bands enables much better coverage to be achieved especially when the nodes are within buildings

back In August 2015, the GSMA (Groupe Speciale Mobile Association)—a group made up of mobile operators—announced that it plans on standardizing LPWAN technology on a licensed spectrum by early 2016. This push has received endorsements and backing from companies like“AT&T, Bell Canada, China Mobile, China Telecom, China Unicom, Deutsche Telekom, Etisalat, KDDI, NTT DOCOMO, Ooredoo, Orange, Singtel, Telecom Italia, Telefonica, Telenor, Telstra, and Vodafone,”

but still, it has not got licensed because of some technical challenges which we will talk about later. 

In Lora low data rates are used, because of low data rates, low bandwidths are required.A variety of bandwidths are available: 7.8 kHz; 10.4 kHz; 15.6 kHz; 20.8 kHz; 31.2 kHz; 41.7 kHz; 62.5 kHz; 125 kHz; 250 kHz; 500 kHz . this bandwidth can be selected upon link condition and data rate

The Lora Network Diagram : 

Node:
The nodes are the sensing elements. Nodes to Gateway is typically a star-topology.
Communication to endpoint nodes is generally bi-directional, but it is also possible to support multicast operation, and this is useful for features such as software upgrades and the like or other mass distribution messages. Nodes can be of the following types 

1. Class A - bi-directional end-devices
2. Class B - bi-directional end-devices with scheduled receive slots
3. Class C - bi-directional end-devices with maximal receive slots 

LoRa gateway :   
The gateway receives the packets from the LoRa nodes/ endpoints and then transfers them onto the network server. This part of can be Ethernet, cellular, wifi or any other telecommunications link wired or wireless. The gateways are connected to the network server using standard IP connections. In this way the data uses a standard protocol, LoRa gateways may often be co-located with a cellular base station.
Gateways within the same network require synchronization.  Communication between end devices and gateways is spread out on different frequency channels and data rates. The selection of the data rate is a trade-off between communication range and message duration.


Network Server: One of its core responsibility is to eliminate duplicate packets.The network server can manage the data rate and RF output for each end device individually by means of an adaptive data rate (ADR) scheme that is typically updated once every 24 hours

Application Server: is truly dependent upon your application 

Possible Application areas : 

·        Smart Parking

·        Environmental monitoring & Agriculture 

·        Waste management

·        Street Lightning

·        Asset tracking

·        Postpaid based Utility meters mainly water and gas meters                                              

·        Flood monitoring

·        Railway Level crossing

·       

Interesting projects around Lora:                            

• Maybe CISCO is making home based router that will have Lora module inside may be the router will work as a gateway
• Amsterdam Beacon Mile https://www.youtube.com/watch?v=w7yF1ONDp7A
• UK Calderdale Flood Sensor Network https://www.youtube.com/watch?v=TxMpNsS-oro [built by things network hardwares] 

The All wanted Location tracking topic: 

Geolocation is a part of the Lora Standard . and sagemcom is a company working on it.

Basically, At the physical layer, the radio signal used by LoRa is somewhat close to a radar signal, thanks to its Chirp Spread Spectrum (CSS) technology. The antenna Gateway can very precisely detect the arrival of the signal emitted from the device, it was explained by Thierry Listable.

By DTOA (difference time of arrival) technology the base station can record the time of arrival of the signal from the device and a position is calculated from that. Obviously, static position is appropriate for the case of Lora 
Semtech says resolution could be from 10m to 100m but Sagemcom says it could be more precise and they are working on a protocol named femtoLora

A company named iota tracker has already announced a product based on it
ref:

http://www.iotatracker.com/howitworks
https://www.youtube.com/watch?v=x4Ic92efLY8 


To use it you need to buy their Home base station which is actually a compact gateway, maybe they won't create the network by increasing the number of users.

LinkLabs has a  statement on this topic to https://www.link-labs.com/lora-localization/  I assume it could be a market hype only So this topic needs more study obviously.

Security of Lora Wan: 
you can listen to this talk regarding the security of Lora
https://www.youtube.com/watch?v=iZOfGGCw90M 

Lora Chip manufactures: (Node)

·        Microchip http://www.microchip.com/wwwproducts/en/RN2483

·        Semtech http://www.semtech.com/wireless-rf/lora.html [has a concentrator chip also (gateway)]

·        niceRf   http://www.nicerf.com/product_146_136.html [actually uses semtech chips]

semtech ships are lower in price than microchip          

Gateway:

·        CISCO 910 industrial router http://www.cisco.com/c/en/us/products/collateral/routers/900-series-industrial-routers/datasheet-c78-732129.html

its obvious that new technology devices cost would be very much so The Things network has come up with lora products which are comparatively low . its all open software and open hardware but its actually for development and these are based on Microchip’s Lora modules

·        https://shop.thethingsnetwork.com/index.php/product/the-things-gateway/

·        https://shop.thethingsnetwork.com/index.php/product/the-things-uno/

·       similarly Froggyfactory sells development alike devices like the things network based on semtech  chips

·        http://www.froggyfactory.com/froggy/index.php

·        http://www.multitech.com/brands/multiconnect-conduit

Lora based LPWAN solution Selling Companies:  these companies are selling network services (Server + Application server) part of LoraWan

·        https://www.link-labs.com/

·        https://www.actility.com/technology/

·        https://www.loriot.io/

·        http://www.froggyfactory.com/froggy/

      Technical challenges of Lora 

      I think the cost and hassle to build and maintain the network infrastructure is what that will prevent Lora from acquiring mass acceptance . Sigfox or NB-IOT will solve this problem as network operator it self will build & support the sub GHz infrastructure along with their 3G/4G cellular services. So now lets see what the future holds for the LPWAN market 

Read More

shared Clipboard / Shared Folder Fix in VirtualBOX VM

Are you a person who has to work on both windows and linux ? Probably you have windows running as host and linux as guest, in my case I have installed lubuntu as guest using virualBOX

Now it would be very convenient if you can copy paste text from host to guest or guest to host. The following steps will guide you through it

in my case Lubuntu is guest while running windows 10 as host
Firstly enable bidirectional mode to both drag and drop & shared clipboard at VirtualBox Manager settings
Settings>advanced 
Both shared clipboard and drag and drop should be checked

Secondly virtualbox guest additions should be running
So start your VM , In my case it is lubuntu .
1. If it is running in scaled mode. Then disable it by pressing Right CTRL(host) + C 
2. From top menu   Devices > Insert Guest additions CD image

In your Lubuntu VBOX will pop up if not open the vBox

Now create a folder in desktop “Guest-Additions” and then copy paste the contents of the vBox to it After that open terminal in this folder and run the following

$ sudo apt-get install gcc make
$ sudo ./VBoxLinuxAdditions.run
$sudo reboot

Now you can copy paste text from guest to host or host to guest

---------------------------------------------------------------------------------------------------------------

Shared Folder fix in virtual Box 

 Like before make sure vBox guest Additions is installed 

1. Shutdown your VM os if it is running
2. Go to settings of the VM and config the shared folder settings , give the path of the folder [host] which you want to share with the guest , here i have created vBox_shared folder in C

Now start the VM

1. First make a folder in the /mnt directory. This folder will hold the contents of the host folder which you want to share with the guest 
2.  Then run the vboxsf command to merge 

Now you will be able to access the folder [vBox_shared] shared by the host in your guest at /mnt/vBoxShared directory 

You have to run the command each time you login 

Read More

what is LPWAN ?

A lot of buzz nowadays around Lora, sigfox, NB-IOT and other LPWAN based technologies. this short post is about a basic introduction on the LPWAN technologies 

LPWAN means low power wide area network LPWAN technology is perfectly suited for connecting devices that need to send small amounts of data over a long range, while maintaining long battery life.

Lets see the following range vs power usage graph to see where LPWAN stands with othe communication technologies like Bluetooth , wifi , zigbee and others 

So LPWAN has the following characteristics:

• Low power (between 5 to 10 years)
• Range in kilometers (up to 10Km)
• Low bit-rate: Less than 5,000 bits per second. Often only 20-256 bytes per message are            sent several times a day.
• Clever modulation
• Cheap

LPWAN technologies can be sub divided into the following categories:

1. UNB
2. (NB-iot, NB-Ciot, LTE-iot)
3.  Lora

UNB	Cellular NB (narrowband)	Lora
Sigfox	NB-iot	Lora Alliance
Telensa	NB-Ciot	LinkLabs
Nwave	LTE-iot
eightless
Hardware Manufacturers
Texas instruments (Sigfox)	Qualcomm	Semtech
Atmel (Sigfox)	Intel	ST electronics (semtech licence )
Samsung (Sigfox)		Microchip (semtech licence )
Silicon labs (Sigfox)

Read More

Callgraph generation using gcc, egypt & graphviz

In this post, we will see how to use gcc, egypt & graphviz to generate call graphs of any C-based source code / multiple source codes. This technique will be helpful if you are working on legacy code and want to have a view of the code architecture at first.

Among the three tools mentioned above, GCC is generally pre-installed in Linux. So You need to install the other two. 

Follow the following :

1. Download Egypt from here egypt download and then unzip it

~/Downloads$ tar -xzvf egypt-1.10.tar.gz ~/Downloads$ sudo mv egypt-1.10 /opt

go to the egypt directory then install it by these commands

/opt/egypt-1.10$ perl Makefile.PL /opt/egypt-1.10$ make /opt/egypt-1.10$ sudo make install

2. then install graphViz by

$sudo apt-get install graphviz

Alright then tools are installed So now let's go to the basics 

In order to generate call graph, you basically need the following steps 

1. compile and generate object files using gcc

2. generate RTL from the object files using gcc

3. generate the call graphs using egypt & graphviz 

RTL means Register transfer Language. It is used to describe the data flow at the register transfer level. It is actually a kind of intermediate representation that is very close to assembly language. 

First of all compile and run a simple C program with an additional file 

$mkdir test
$cd test
$notepadqq hello.h
$notepadqq hello.c
$notepadqq main.c

#include <stdio.h> #include "hello.h" void main(int argc, char const *argv[]) {     printf("I am the Main Function\n");     hello_world(); }

main.c

#ifndef HELLO_H #define HELLO_H void hello_world(void); #endif

hello.h

#include <stdio.h> #include "hello.h" void hello_world(void) {     printf("hello world\n"); }

hello.c 

Now let’s compile using GCC 

$gcc -Wall main.c hello.c -o hello $./hello

Now generate the RTL expands and run egypt command on the output to get a callgrqaph picture 

$gcc -fdump-rtl-expand main.c hello.c $egypt main.c.192r.expand hello.c.192r.expand | dot -Grankdir=LR -Tsvg -o hello.svg

now open the svg file and you will see the pictorial call graph of the hello application that you made

Read More

ARM Cortex-M0 : Introduction

Well we designers come to a point when we want to go to the next level of embedded designing and we start to think about ARM based microcontrollers. So what is ARM ?

Actually ARM is a processor and the processor core is  sold by the company also named ARM to different vendors like STM , Texas Instruments , Atmel and so on . So these vendors do what ?
well instead of re designing the processor these compnaies make microcontrollers around the ARM processor . & we developers choose microcontroller from these vendors and start using it.

So why would all the vendors choose ARM ?

Because ARM ( advanced RISC machine) is a family of reduced instruction set computing architectures and requires less number of transistors than typical complex instructions set computing architecture s (CISC) . This approach reduces cost , power consumption and heat . for example ARM cortex M0 has 12,000 logic gates & even a 32 bit multiplication can be completed in 1 cycle. some of the important features are below:

Features: 

• Cortex- M processors are extremely C friendly
• increased performance and efficiency 
• Low cost
• extended battery life
• floating point 
• DSP capability 
• Lower operating frequency means : lower active power & lower EMI

More information on  ARM cortex M processor: 

• Remember ARM cortex M0 is a processor, Cortex M0 is designed as an ideal C target  
• Cortex M0 has 56 instructions 
• user can choose devices with smaller flash memory sizes for the the same application 
• The ARM Cortex-M1 processor is the first ARM processor designed specifically for implementation in FPGAs. 
• Cortex M0 processor is a 32 bit RISC (reduced instruction set computing) processor with Von neuman Architecture 
• clock frequency for the cortex M0 processor can be reduced significantly to achieve lower power consumption 
• Cortex M0 processor has implemented the ARMv6-m architecture 

Some Abbreviations:  

ASSP: Application Specific Standard products
SOC: System on chip
ARM:  originally Acorn RISC Machine , later Advanced RISC Machine
NVIC: Nested Vector Interrupt Controller
MDK: Microcontroller development Kit
AMBA: Advanced Microcontroller BUS architecture
AHB: Advanced High performane BUS
APB: Advanced peripheral Bus


Instruction sets : 

ARM cortex M processors supports 2 types of instructions sets

• 32 bit instruction set ----------- called ARM instruction set 
• 16 bit instruction set ----------- called Thumb instruction set 

for example ARM7TDMI supports both types of instruction sets 

Most instructions generated by the C compiler use the 16 bit instructions & 32 bit instructions are used when the 16-bit version cannot carry out the required operations. 

Interrupt types: 

Maskable Interrupt: The interrupts which can be ignored by the processor 

NMI(Non maskable interrupt): the interrupts that can not be ignored by the processor



Cortex M0 block diagram: 

Processor Core elements :

• Register Banks
• ALU(arithmetic logic unit)
• Control Logic 

AHB Lite Bus interface: is a on chip bus protocol used in many ARM processor . it is part of the AMBA ( Advanced Microcontroller BUS architecture) specification . it is 32 bits wide .

• APB means Advanced Peripheral Bus and you can see peripherals are attched with this BUS 
• AHB Lite supports 32,16,8 bit transfers

Unlike AHB lite APB does not support different sized transfers So APB should be accessed using word sized transfers 

                                           In ARM Word is 32 bits wide 

Read More

Event Driven Embedded Programming

Introduction

I guess most of us as beginners in embedded systems programming in C++, probably start writing firmware with a super loop like architecture where

• all our statements/function calls reside in the main loop 
• we start including arduino like libraries 
• we create global objects & start using the objects in the main loop.  
• being a bit more mature & in order to manage evolving large code base we bring hierarchical models  to subgroup our code across different classes 

Fundamentally the code executes in a loop but the code is more manageable now.

The problem with the super loop is that it is not a very good approach to attain hard real-time performance and is not suited for the embedded applications where you need hard/soft real-time response. So what could be the solution?

The concept of RTOS

The firmware industry has a long history of being written in C with the RTOS approach, for example, VxWorks , freeRtos are very popular and robust. Obviously, RTOS is better than Super Loop considering real-time operation

RTOS types

RTOS is of two types: cooperative and preemptive

In Co-operative RTOS each task must finish before the time allotted for the completion of the task gets over. Meaning there should not be any blocking part in the code. There is an excellent book named “Patterns for Time-triggered Embedded Systems” by Michael J point where many design patterns have been shown to design embedded software using Co-operative RTOS. The author also suggests why a cooperative scheduler can be more effective and reliable than a preemptive scheduler if properly implemented.

On the other hand In preemptive RTOS Tasks can have blocking parts and in this part, context switching i.e. task switching can occur. Task switching can also occur in the middle of a task execution if a higher priority task is needed to be executed. This is called preemption.   When a preemption occurs the RTOS saves the current tasks states and then switches to another task. So usage of RAM is an issue here and also other complexity arises. Free RTOS is a well popular preemptive RTOS.

Remember CO-operative RTOS has also priority-based operation capability.

The concept of Active Object

As a firmware engineer, I always wanted to have a combination of all the best options out there. For instance i want to use some of the C++ & OOP features , use arduino ready made libraries & also use RTOS like scheduler to achieve soft/hard real time operation. 

Looking around i found Event-driven programming & active object concepts from Miro Samek, he is renowned in the embedded software industry. He created the Active object framework.

Active object has the following properties:

• Encapsulated 
• Non-blocking 
• HSM (hierarchical state machine) 
• Event queues 
• Event Publish and subscribe capability 

Miro samek’s quantum leaps offers Active object framework solution for different microprocessor architectures. They also offer modelling tools to generate code from UML diagrams. Currently these are the frameworks provided by quantum leaps:

• QP-nano
• QP-C
• QP-C++

These frameworks can work with 2 types of kernels underneath these are:

• Cooperative kernel (QV) (much like co-operative RTOS) 
• Preemptive Non-Blocking Kernel (QK) (much like preemptive RTOS but with non-blocking code)

There is an excellent document by miro samek named “beyond the RTOS” to explain the concepts

A minimum Event driven framework looks like this

1. void loop()
2. {
3.     if( event1() ) { Event_1_handler(); }
4.     else if( event1() ) { Event_1_handler(); }
5.     else if( event1() ) { Event_1_handler(); }
6.     else
7.     {
8.         goTo_idleState();
9.     }
10. }

Here the framework/ Supervisory event driven infrastructure waits for events
and dispatches them to application

Some important notes

• Calls to functions that poll internally (like delay()) are not allowed, because they would slow down the main loop and defeat the main purpose of event-driven programming
• The Event handler code MUST consist of Linear code that quickly returns control to the framework after handling each event 
• The event handler code must be designed in a way so that the event handler can pick up where it left for the last event. But to do this you need if-else branches and code is likely to become “spaghetti code “. The solution is concept of state machine 
• Qp –nano framework allows to combine event driven programming with state machines 
• In qp-nano framework there is multiple event queues  with priority property 
• There is a  state machine corresponding to each event 
• These Event queues are constantly monitored by a scheduler 
• Scheduler picks up the highest priority not-empty queue , after finding it > the scheduler extracts the event from the queue and sends it to the state machine associated with it . This is called dispatching of an event to the state machine 
• The design guarantees that the dispatch() operation for each state machine always runs to completion and returns to the main Arduino loop before any other event can be processed

The event queue + state machine + a unique priority is collectively called an Active Object

• When all event queues are empty the situation is idle condition . in this case QV_onIdle() is called , here processor can go to a low power sleep mode 

Conclusion

I think event driven programming is good for battery powered applications

I wish to work with this Active object framework at near future and write a blog post describing my hands on experience

Read More