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