KEIL RTOS BASED EMBEDDED WEB SERVER FOR REAL TIME ......Real Time Operating System is an Operating (RTOS) System used for real time ... This depicts deterministic timing behaviour

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 10, October 2017, pp. 553–560, Article ID: IJMET_08_10_062

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=10

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

KEIL RTOS BASED EMBEDDED WEB SERVER

FOR REAL TIME INDUSTRIAL MONITORING

A.Yogaraj

Associate Professor ECE, veltech Dr RR& Dr SR University, Chennai

C.S.Sivanthiram

Assistant Professor ECE, Sree Sastha College of Engineering and Technology, Chennai,

S.Dhanjeyan

Assistant Professor EEE, Veltech Multitech Engineering College Chennai

S.Suresh

Assistant Professor ECE, Sree Sastha College of Engineering and Technology Chennai

ABSTRACT

With the advent of smart systems in industries and the number of catastrophic

incidents occurring in day to day basis, real time monitoring and controlling actions

in a timely manner in case of emergency scenarios is a challenging and an important

issue to be considered. Moreover, the scheduling of the parameters monitored and

taking the control action in the smallest possible delay, the priority assignment and

scheduling of the monitoring and actuation must be done in a deterministic nature to

avoid catastrophes. The design of a real time data acquisition system is done using

ARM processor and built-in web server application. A reliable scheduling mechanism

with multitasking functionality is needed for handling multiple processes. The main

essence of this project is to design and implement an embedded web server for data

acquisition and controlling system using ARM CORTEX M3 CORE(LPC1768)

running on Keil RTX and TCP/IP Ethernet connection for industrial monitoring

applications that could prevent accidents. The LPC 1768 board acts as an embedded

web server and the data from the sensors which are simulated to measure different

parameters is communicated to the Central Monitoring System via ETHERNET.

Keywords: Keil RTX, Ethernet, multitasking, data acquisition

Cite this Article: A.Yogaraj, C.S.Sivanthiram, S.Dhanjeyan and S.Suresh, Keil

RTOS based Embedded Web Server for Real Time Industrial Monitoring,

International Journal of Mechanical Engineering and Technology 8(10), 2017,

pp. 553–560.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=10

A.Yogaraj, C.S.Sivanthiram, S.Dhanjeyan and S.Suresh


1. INTRODUCTION

Since the systems in industries are very complex it is required to monitor the system state in

real time. To make the system more flexible, microcontroller can be used for the system

design which could make the system more reliable enhancing the performance of the system.

The advanced RISC machines (ARM) architecture is based on Reduced Instruction Set

Computer (RISC) principles, and the instruction set and related decode mechanism are much

simpler than those of micro programmed Complex Instruction Set Computers (CISC). This

simplicity results in a high instruction throughput and impressive real-time interrupt response

from a small and cost-effective processor core.

Real Time Operating System is an Operating (RTOS) System used for real time

application for processing of data without any delays. RTOS is on computational environment

that gives response or reaction for an event in a specific time. It depicts not only on the logical

correctness but as well on the time correctness of the system. The deadline for producing the

result is depicted at the instant of time evolution of an event.

Operating System (OS) is a system program that acts as an interface between the hardware

and the application programs. The common features of OS comprise of: Synchronization,

Multitasking, Inter-task Communication, Interrupt and Event Handling, Input/ Output, Timers

and Clocks and Memory Management. Thus RTOS is an operating system that is used in real-

time applications and embedded systems for providing logically correct result before the

deadline. This depicts deterministic timing behaviour and resource utilization of an RTOS.

Real time kernel is simple and stable. RTOS can cut a complex application into several

mutually independent tasks based on task priority and it also has its own limitations. RTOS,

include the task management, task scheduling, interrupt handling etc.

Industrial application requires multiple tasks to be executed. Controlling the industrial

system, processing of data, storing of the data and transmission of the data with polling

technique require more time so use of multi-tasking is involved. When ARM processor

combined with RTOS with timing constraint can be realized for the data acquisition and

transmission of data.

2. DESIGN METHODOLOGY

The system is based on ARM processor running on Keil RTX. The web server configuration

is based on CGI scripting which gives the interface between the system and the software.

A. Proposed Architecture

Most of the controlling applications are designed with processor based real-time embedded

systems. This system is design to monitor the various parameters of an industry such as

temperature, pressure, humidity, etc. The real time embedded system continuously senses

these parameters by carrying out these tasks with certain timing constraints making the

system real time. The proper scheduling mechanism is applied after an analysis on various

real time scheduling mechanisms. The data transmission between the sensing areas to the

central monitoring system is carried through an embedded web server with hypertext transfer

protocol (HTTP). This is shown in the Fig.1. The proposed system consists of16/32-bit RISC

microprocessor LPC1768 a product of PHILIPS which is a high performance and cost

effective microcontroller that can be used for general purpose applications.

Keil RTOS based Embedded Web Server for Real Time Industrial Monitoring


B. The Principle of Embedded Web Server

An Embedded web server means importing n internet based Web Server with the support of

proper hardware and software platforms for transferring and monitoring data of distributed

components. It uses TCP/IP protocol as its underlying communication protocol and also it

uses Web server technology as its core technology.

A specifically designed embedded web server is needed to handle multiple user requests

with increased functionality. The Apache web server which is used in Linux is not enough to

handle the multiple user requests. So HTTP based embedded web server can be used which

has high capability. The HTTP web server implements HTTP protocol. With this the

distribution and acquisition of information which has to be displayed through web service

using extensible markup language (XML) or hypertext markup language (HTML) is possible.

Figure 1 Overall System Architecture

The HTTP has other advantages also such as it is cross- platform protocol and HHTP

clients are readily available with all latest computers. The internet of things (IoT) can be

achieved using embedded web server.

C. Data Transmission Using TCP/IP Networking Suite

The Keil MDK has RLTCPnet networking suite as one of its key middleware components in

the RL-ARM library. RLTCPnet library is a full networking suite designed for ARM based

microcontrollers. This networking suite is based on Transmission Control Protocol/Internet

Protocol (TCP/IP) that can be used for private networks. It also consists of Ethernet drivers

for the supported. It supports both UDP and TCP based communication which makes the

networking protocol to be customized.

It also has a feature of adding application layersfor enabling common services, such as

simple mail transfer protocol (SMTP) clients for sending emails, domain name system (DNS)

and dynamic host configuration protocol (DHCP) clients for enabling automatic

configuration. RLTCPnet also enables a microcontroller to act as embedded web server with

HTTP, FTPand TELNET protocols which help in data transmission between server and the

clients. Thus data acquisition and monitoring could be achieved with the TCP/IP networking

suite and the acquired data is displayed in the monitoring system with HTML web page

application.



Figure 2 explains how API functions can be used for TCP connection and data transfer.

The socket communication can be opened in two different modes either passive or active

mode. This can be done using API function “TCPPassiveOpen()” for passive mode and

“TCPActiveOpen()” for active mode. The API function “TCPPassiveOpen()” puts the stack

into “Listen” or “Server” mode and it waits for a connection from a remote host. The API

function “TCPActiveOpen()” will try to establish a connection with a remote host.

The data to be transmitted should be placed in the transmit buffer TCP_TX_BUF after

checking it to be empty. This can be done by checking the flag TX_BUF_RELEASED. Data

is copied into transmit buffer TCP_TX_BUF if it is empty. The number of bytes to be

transmitted should be assigned to the variable TCPTxDataCount. Then the function

TCPTransmitTxBuffer() should be called which sends data to the remote host and then it

clears the TX_BUF_RELEASED flag. After the remote host acknowledges the transmitted

datagram this flag is set again as depicted in Figure 3.

Figure 2 Use of API functions for TCP connection

Figure 3 Transmission of Data

The reception of any new datagram is indicated by the flag SOCK_DATA_AVAILABLE.

If this flag is set, the number bytes received is indicated by the flag TCPRxDataCount.

The data is then copied out of the receive buffer TCP_RX_BUF. The API

TCPReleaseBuffer() should be called to free the receive buffer for the next data. This is

shown in the Figure 4.



Figure 4 Receiving of Data

Figure 5 RTX Tasks & System Window(RR Scheduling)

3. SCHEDULING MECHANISMS USING KEIL RTX

The Keil RTX (Real Time eXecutive) is a free RTOS. Itis a deterministic real time operating

system designed for ARM and Cortex-M devices. It has RL-ARM, the Real View Real-Time

Library (RL-ARM) as one of its components which has real time functions.

A. Round Robin Scheduling

For creating a round-robin-based scheduling scheme the round robin option should be enabled

in the RTX_Config.c file. Each task should be declared with the same priority. The tasks in a

round robin RTOS will run for a fixed period, or time slice, or until they reach a blocking OS

call. The CPU will be allocated to a specific task for a fixed amount of time before executing

the next ready task. If a task blocks before its time slice has expired, the execution will be

passed to the next ready task. The round robin scheduling is done for four tasks and results are

analysed.

Figure 5 shows the RTX tasks and system window where the tasks are listed and their

switching can be seen. In Fig. 6 a graphical representation of timing of each task is shown in

Event Viewer.

B. Priority Pre-emptive Scheduling

The round robin option should be disabled in the RTX_Config.c file. Each task should be

declared with a different priority. Since each task is assigned different priorities the CPU is

allocated to the task which has the highest priority. In a pre-emptive RTOS, the lower priority

task will be pre-empted by a higher priority task and also if it reached a blocking OS call. This



task will run till it is blocked by an event flag, semaphore, or other object. When it blocks, the

next ready task with the highest priority will be scheduled and will run until it blocks, or a

higher priority task becomes ready to run.

The four tasks namelyt_phaseA,t_phaseB, t_phaseC,t_phaseD,are created. The four tasks

are to measure different sensor value like:

• t_phase A - Temperature sensor

• t_phaseB - Pressure sensor

• t_phase C – Humidity sensor

• t_phase D – Gas sensor

The tick timer is set to 10 mS and the round robin timeout is set to 50 mS. The tasking

switching occurs as the time slice.

Figure 6 Event Viewer Window(RR Scheduling)

Figure 7 RTX Tasks & SystemWindow(Pre-emptive Scheduling)

The pre-emptive scheduling is done for three tasks temperature, pressure and humidity

sensors with different priorities and the simulation result of the pre-emptive scheduling is

shown in Figure 7.



4. IMPLEMENTATION OF EMBEDDED WEB SERVER

The web server is implemented on the LPC 1768 board. In this case analysis the

potentiometer is taken as the input. The analog input is given to the ADC which converts the

analog values into digital. The data is then transmitted through the Ethernet to the monitoring

system. The real time value is displayed in the web page. The implementation of web server

in LPC1768 board is shown in the Figure 8.

The HTML pages display the measured values obtained from the web server at the

monitoring system. The real time scheduling mechanism has to be implemented to perform

multi-tasking and to make the system more reliable.

Figure 8 Web Server Implementation

5. CONCLUSION

In this paper, the design of the real time embedded web server based on ARM has been

discussed. Analysis of round- robin and priority pre-emptive scheduling has been done along

with simulation results. The design of data acquisition system is based on web server which

enables data transmission between the instrumentation and Ethernet through existing

computer networks. It also supports CGI which improves system security, enables user

interaction and enhances creation of dynamic web pages.

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Documents

KEIL RTOS BASED EMBEDDED WEB SERVER FOR REAL TIME ......Real Time Operating System is an Operating (RTOS) System used for real time ... This depicts deterministic timing behaviour