Embedded System Architecture 5v204m

Embedded System Architecture

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Embedded System Architecture Every embedded system (ES) is composed of interacting elements (hardware or software). An architecture is a set of representations of those elements and their relationships. Architecture helps understanding the “whys” of the elements with given functionalities. Defining and understanding the architecture of an ES is an essential component of good system design. An architectural systems engineering in an ES • helps understanding the design • is essential to resolve challenges when deg a new system • helps design re-use, reduces design time and cost.2

Embedded System Architecture • An embedded architecture captures various views, which are representations of the system. • It is thus a useful tool in understanding all of the major elements: – Why each component is there? – Why the elements behave the way they do?

• Without an architecture design it is difficult to determine how the system would behave under a variety of circumstances in the real world. • The architecture conveys in some way the critical components in a design and their relationships to each other. Even if the architectural structures are rough and informal, it is still better than nothing. 3

Embedded Systems Model •

The embedded system model indicates that at the highest level, they have – –

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at least one layer (hardware) or all layers (hardware, system software and application software) into which all components fall.

This model is essentially a layered (modular) model of an ES architecture. It gives visual representation of the main elements and their associated functions.

The hardware layer contains all the physical components. The system software layer contains all the software located on the ES. The application software layer contains all the SW being processed by the ES. 4

Network’s Architecture in ES •

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The ES is a networking of internal components and the network’s architecture. Good to associate the networking components with a universal networking model, the seven layer OSI reference model. Data originating at the application layer flow downward through all seven layers. Information (header) is appended to the data at each layer (except for the application and physical layers). Data is wrapped with information for other devices to unwrap and process.

Mapping OSI layers

ES layers

Physical

Hardware

Data-link Network Transport

System SW

Session Presentation Application

Application5 SW

OSI Model and Real World Protocol • The functionalities and methodologies implemented at each layer based on the OSI model are commonly referred to as networking protocols. • It isn’t always the case that there are all seven layers or there is just one protocol per layer. • The functionality of one layer of the OSI model can be implemented in one protocol, or also it can be implemented across multiple protocols and layers. • A group of protocols may have their own name and be grouped together in their own proprietary layers. Examples are: T/IP

WAP Bluetooth

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The T/IP, OSI and ES Models

The T/IP stack is made up of four layers. OSI layers Top three (App, Presentation, Session) Transport layers Network layer Two OSI layers (Data Link and Physical)

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T/IP layers T/IP App layer Transport layer. Internet layer 7 Network access layer

The OSI, WAP and ES Models

The Wireless Application Protocol (WAP) stack provides five layers of upper layer protocols. OSI layers Application layer Presentation layer Session layer Transport layer

   

WAP layers WAP Application layer Security layer Session + Transaction layer 8 Transport layer

The Bluetooth, OSI and ES Models The Bluetooth stack is a three-layer model made up of Bluetooth-specific as well as adopted protocols from other network stacks, such as WAP and/or T/IP . OSI layers

Bluetooth layers

Physical and Lower Data Link layers

Transport Protocol Group

Upper Data link, Network + Transport layer

Middleware Protocol Group

Session, Presentation + Application layer

Application Protocol Group 9

(1) Physical Layer Protocols in the ES Models

The Physical Layer represents all of the networking HW physically located in an embedded device. It defines, manages, and processes, via hardware, the actual voltage representations of 1’s and 0’s. Physical layer protocols defining the networking hardware of the device are located in the hardware layer of the ES model. Physical layer protocols are classified as either LAN or WAN protocols. They can be further subdivided according to the transmission medium connecting the device to the network (wired or wireless). 10

(2) Data-Link Layer Protocols in the ES Data-link layer protocols are implemented in the system software layer. Closest to the hardware layer.

Includes any software needed to control the hardware. Bridging also occurs at this layer. Data-link layer protocols can be used for (i) LAN, (ii) WAN, or (iiii) both. Can be wired or wireless. Generally, reliant on a specific physical layer. May also be ported to very different mediums. s hardware-independent upper-data-link functionality.

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(3) Network Layer Protocols in the ES Implemented in the system software layer. Is typically hardware independent. Depends only on the data-link layer implementation.

Networks can be divided into smaller sub-networks, called segments. Devices within a segment communicate via their physical addresses. Devices in different segments communicate through an additional address, called the network address. Conversion between physical addresses and network addresses can occur in the data-link layer protocols (i.e. ARP, RARP etc.) Network layer protocols can also convert between physical and network12 addresses as well as assign network addresses.

(4) Transport Layer Protocols in the ES Transport layer protocols sit on top of and are specific to the network layer protocols. Are typically responsible for communication between two specific devices (point-to-point) communication.

Ensures reliable point-to-point data transmission, by ensuring that: 1. packets are received and transmitted in the correct order 2. transmitted at a reasonable rate 3. packets are not corrupted 4. Provides acknowledgement on receiving 5. Requests retransmission in case of detection of error.

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(5) Session Layer Protocols in the ES The connection between two networking applications on two different devices is called a session. The management of a session is handled by the session layer.

Generally, sessions are assigned a port (number). The session layer protocols 1. Separate and manage each session’s data 2. Regulate the data flow of each session 3. Handle any error 4. Ensure the security of the session 5.

14 Ensure that the two applications involved in the session are the right applications.

(6) Presentation Layer Protocols in the ES Protocols in the presentation layer are responsible for translating data into formats that higher applications can process.

1. Presentation layer protocols are usually implemented in networking applications in the application software layer in ES. 2. Data compression/decompression, data encryption/decryption, data protocol/character conversions. 15

(7) Application Layer Protocols in the ES

1. A device initiates a network connection to another device at the application layer. 2. Application layer protocols are either used directly as network applications by end-s or the protocols are implemented in end- network applications. 16 3. These applications “virtually” connect to applications on other devices.