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In the day-to-day life we come across a wide variety of consumer electronic products. Common examples are Mobile Phones, Washing machines, FAX machines, Xerox machines, TV Remote Controllers etc. Each of these devices does have one or more programmable devices waiting to interact with the environment as effectively as possible. These are a class of "embedded systems" and they provide service without much delay in real time
Features of Mobile phone :
When we want to purchase any of them we look for the following features
Price , weight, size, screen, games, camera , radio , ringtones and memory . besides these features it also includes network type GSM and CMDA ( Bandwidth) .A mobile phone is a very complex device which houses a number of miniature gadgets functioning coherently on a single device. Moreover each of these embedded gadgets such as digital camera or an FM radio along with the telephone has a number of operating modes such as:
â€¢ you may like to adjust the zoom of the digital camera,
â€¢ you may like to reduce the screen brightness,
â€¢ you may like to change the ring tone,
â€¢ you may like to relay a specific song from your favorite FM station to your friend using your mobile
â€¢ You may like to use it as a calculator, address book, emailing device etc.
These variations in the functionality can only be achieved by a very flexible device. This flexible device sitting at the heart of the circuits is none other than a Customized Microprocessor better known as an Embedded Processor and the mobile phone housing a number of functionalities is known as an Embedded System.
Real time usually means time as prescribed by external sources
A number of systems coexist to discharge a specific function in real time
Characteristics of RTEs:
The RTES is usually meant for very specific functions. Generally a special purpose microprocessor executes a program over and over again for a specific purpose. If the user wants to change the functionality, e.g. changing the mobile phone from conversation to camera mode or calculator mode the program gets flushed out and a new program is loaded which carries out the requisite function. These operations are monitored and controlled by an operating system called as Real Time Operating System (RTOS)
The constraints on the design and marketability of RTES are more rigid than their non-real-time non-embedded counter parts. Time-domain constraints are the first thing that is taken care while developing such a system. Size, weight,
power consumption and cost4 are the other major factors.
Reactive and Real Time
Many embedded systems must continually react to changes in the system's environment and must compute certain results in real time without delay
In general, a cell phone is composed of the following components:
â€¢ A Circuit board â€¢ Antenna â€¢ Microphone â€¢ Speaker â€¢ Keyboard â€¢ Battery
â€¢ Liquid crystal display (LCD)
Cell phone circuitry
A typical mobile phone handset should include standard I/O devices (keyboard, LCD), plus a microphone, speaker and antenna for wireless communication. The Digital Signal Processor (DSP) performs the signal processing, and the micro-controller controls the user interface, battery management, call setup etc. The performance specification of the DSP is very crucial since the conversion has to take place in real time. This is why almost all cell phones contain such a special processor dedicated for making digital-to-analog (DA) and analog-to-digital(AD) conversions and real time processing such as modulation and demodulation etc. The Read Only Memory (ROM) and flash memory (Electrically Erasable and Programmable Memory) chips provide storage for the phone's operating system (RTOS) and various data such as phone numbers, calendars information, games etc.
A Design Metric is a measurable feature of the system's performance, cost, time for implementation and safety etc. Most of these are conflicting requirements i.e. optimizing one shall not optimize the other: e.g. a cheaper processor may have a lousy performance as far as speed and throughput is concerned.
Following metrics are generally taken into account while designing embedded systems
NRE cost (nonrecurring engineering cost): It is one-time cost of designing the system.
Unit cost: The monetary cost of manufacturing each copy of the system, excluding NRE cost.
Size: The physical space required by the system, often measured in bytes for software, and gates or transistors for hardware.
Performance: The execution time of the system
Power Consumption: It is the amount of power consumed by the system, which may determine the lifetime of a battery, or the cooling requirements of the IC, since more power means more heat.
Flexibility: The ability to change the functionality of the system without incurring heavy NRE cost. Software is typically considered very flexible.
Time-to-prototype: The time needed to build a working version of the system, which may be bigger or more expensive than the final system implementation,.
Time-to-market: The time required to develop a system to the point that it can be released and sold to customers. The main contributors are design time, manufacturing time, and testing time..
Maintainability: It is the ability to modify the system after its initial release, especially by designers who did not originally design the system.
Correctness: This is the measure of the confidence that we have implemented the system's functionality correctly.
The Performance Design Metric: Performance of a system is a measure of how long the system takes to execute our desired tasks.
The two main measures of performance are:
Latency or response time:
This is the time between the start of the task's execution and the end. For example, processing an image may take 0.25 second.
This is the number of tasks that can be processed per unit time. For example, a camera may be able to process 4 images per second
Digital Signal Processor:
Signals represented digitally as sequences of samples . Digital signals obtained from physical signals via transducers (e.g., microphones) and analog-to- digital converters (ADC) .Digital signals converted back to physical signals via digital-to-analog converters (DAC) . Digital Signal Processor (DSP): electronic system that processes digital signals
DSP : TI 3206711, TI 3205000 , TMS32010
TMS 32010 has got the following features
â€¢ 16-bit fixed-point
â€¢ Harvard architecture separate instruction and data memories
â€¢ Specialized instruction set Load and Accumulate
â€¢ 390 ns Multiple-Accumulate(MAC)
General characteristics of Digital Signal Processor
Microprocessors specialized for signal processing applications
Two to Four memory accesses per cycle
Dedicated hardware performs all key arithmetic operations in 1 cycle
Very limited Single Instruction Multiple Data features
Multiple operations per instruction
Dedicated address generation units
Specialized addressing Hardware looping.
Interrupts disabled during certain operations
Limited or no register Shadowing
Rarely have dynamic features
Relatively narrow range on-chip peripherals and I/O interfaces
synchronous serial port
It deals with interface between the device and the environment
Microcontroller: Intel 8051, Intel 80196, Motorola 68705
Some Specifications of the Processor MCS96
Frequency of Operation: 40 MHz
2 Mbytes of linear address space
1 Kbyte of register RAM
3 Kbytes of code RAM
8 Kbytes of ROM
2 peripheral interrupt handlers (PIH)
6 peripheral interrupts
83 I/O port pins
2 full-duplex serial ports with baud-rate generators
Synchronous serial unit
8 pulse-width modulator (PWM) outputs with 8-bit resolution
16-bit watchdog timer
Sixteen 10-bit A/D channels
Programmable clock output signal
Characterization of General Purpose Processor
CPUs for PCs and workstations E.g., Intel Pentium IV
Von Neumann architecture
Typically 1 access per cycle
Most operations take more than 1 cycle
General-purpose instructions Typically only one operation per instruction
Often, no separate address generation units
General-purpose addressing modes
Software loops only
Interrupts rarely disabled
Register shadowing common
Dynamic caches are common
Wide range of on-chip and off-chip peripherals and I/O interfaces
Asynchronous serial port...
The memory may be Read-Only-Memory or Random Access Memory (RAM). To reduce the access (read-write) time a local copy of a portion of memory can be kept in a small but fast memory called the cache memory. The memory also can be categorized as Dynamic or Static. Dynamic memory dissipates less power and hence can be compact and cheaper. But the access time of these memories are slower than their Static counter parts. In Dynamic RAMs (or DRAM) the data is retained by periodic refreshing operation. While in the Static Memory (SRAM) the data is retained continuously. SRAMs are much faster than DRAMs but consume more power. The intermediate cache memory is an
An m word memory can store m x n: m words of n bits each. One word is located at one address therefore to address m words we need.
K = Log2(m) address input signals; k number address lines can address m = 2k words
Example 4,096 x 8 memory:
â€¢ 32,768 bits
â€¢ 12 address input signals
â€¢ 8 input/output data signals
There are two important specifications for the Memory as far as Real Time Embedded Systems are concerned.
- Write Ability
- Storage Performance
Write ability: It is the manner and speed that a particular memory can be written
High end - Processor writes to memory simply and quickly e.g., RAM
Middle range - Processor writes to memory, but slower e.g., FLASH, EEPROM
Lower range - Programmer must write to memory e.g., EPROM, OTP ROM
Low end - Bits stored only during fabrication e.g., Mask-programmed ROM
Storage Performance: It is the ability to hold the stored bits.
High end - Essentially never loses bits e.g., mask-programmed ROM
Middle range - Holds bits days, months, or years after memory's power source turned off e.g., NVRAM
Lower range - Holds bits as long as power supplied to memory e.g., SRAM
Low end - Begins to lose bits almost immediately after written e.g., DRAM
Better write ability
Can be in-system programmable with built-in circuit to provide higher than normal voltage
Built-in memory controller commonly used to hide details from memory user Writes very slow due to erasing and programming
"Busy" pin indicates to processor EEPROM still writing
Can be erased and programmed tens of thousands of times
Similar storage permanence to EPROM (about 10 years)
Far more convenient than EPROMs, but more expensive
Same floating gate principle and same write ability and storage permanence like EEPROM
It can be erased at a faster rate i.e. large blocks of memory erased at once, rather than one word at a time.
Entire block must be read, word updated, then entire block written back
Used with embedded systems storing large data items in nonvolatile memory
Used in digital cameras, TV set-top boxes, cell phones
Input/Output Devices and Interface Chips:
To generate an analog signal from the microprocessor Digital to Analog Converter(DAC) is needed and to accept analog signal we need and Analog to Digital Converter (ADC). These DAC and ADC again have certain control modes. They may also operate at different speed than the microprocessor. To synchronize and control these interface chips we may need another interface chip. These chips serve as relaying units to transfer data between the processor and input/output devices. The input/output devices are generally slower than the processor. Therefore, the processor may have to wait till they respond to any request for data transfer. Number of idle clock cycles may be wasted for doing so. However, the input-output interface chips carry out this task without making the processor to wait or idle.
ADC and DAC:
Measurand is the quantity which is measured. In this case it is the analog speech signal. The sensor is a microphone. The conditioner can be a preamplifier or a demodulator. The Analog Processor mostly is a Low Pass Filter (LPF). This is primarily used to prevent aliasing.The following is the Analog to Digital Converter which has a number of stages to convert an analog signal into digital form. The Digital Signal Processing is carried out by a system with a processor. Further the processed signal is converted into analog signal by the Digital to Analog Converter which finally sends the output to the real world through another Low Pass Filter.
DA Converter: Pulls the samples from memory and convert them into an impulse train.
Ans: No. of bits (8-bits, 16-bits etc), No. of channels, Conversion Time, Power Supply range, Power Consumption, Various Temperature ratings, Packaging
AD Converter: It consists of a sampler, quantizer and a coder
Sampler - Tries to maintain a constant voltage till the next switching
Quantizer - Convert the voltage to a binary number. The number of bits in a binary number decides the approximation and accuracy.
Coder - responsible for packing several samples and transmitting them onwards either in synchronous or in asynchronous manner.
No. of bits (8-bits, 16-bits etc), Settling Time, Power Supply range, Power Consumption, Various Temperature ratings, Packaging
Sampling frequency must be twice that of maximum frequency
The following table illustrates the properties of wireless communication used in mobile phones
Like a computer operating system, a mobile operating system is the software platform on top of which other programs run. The operating system is responsible for determining the functions and features available on your device, such as thumbwheel, keyboards, WAP, synchronization with applications, e-mail, text messaging and more. The mobile operating system will also determine which third-party applications can be used on your device. Some of the more common and well-known Mobile operating systems include the following:
Symbian OS is used Nokia mobile phone. Symbian is a joint venture originally set up by Ericsson, Nokia and Psion to develop an industry standard operating system for mobile multimedia terminals.
It is currently owned by Ericsson (15.6%), Nokia (47.9%), Panasonic (10.5%), Samsung (4.5%), Siemens AG (8.4%), and Sony Ericsson (13.1%).
It has become a standard operating system for smartphones, and is licensed by more than 85 percent of the world's handset manufacturers. It is designed for the specific requirements of 2.5G and 3G mobile phones.
The Windows Mobile platform is available on a variety of devices from a variety of wireless operators. You will find Windows Mobile software on Dell, HP, Motorola, Palm and i-mate products. Windows Mobile powered devices are available on GSM or CDMA networks.
Since the introduction of the first Palm Pilot in 1996, the Palm OS platform has provided mobile devices with essential business tools, as well as capability to access the Internet or a central corporate database via a wireless connection.
The first company to launch phones with Linux as its OS was Motorola in 2003. Linux is seen as a suitable option for higher-end phones with powerful processors and larger amounts of memory
MXI is a universal mobile operating system that allows existing full-fledged desktop and mobile applications written for Windows, Linux, Java, Palm be enabled immediately on mobile devices without any redevelopment. MXI allows for interoperability between various platforms, networks, software and hardware components.
A fail-safe mechanism that intervenes if a system stops functioning. A hardware timer that is periodically reset by software. If the software crashes or hangs, the watchdog timer will expire, and the entire system will be reset automatically.
The watchdog timer is a 16-bit internal timer that resets the microcontroller if the software fails to operate properly.
A common problem is for a machine or operating system to lock up if two parts or programs conflict, or, in an operating system, if memory management trouble occurs. In some cases, the system will eventually recover on its own, but this may take an unknown and perhaps extended length of time.
A watchdog timer can be programmed to perform a warm boot (restarting the system) after a certain number of seconds during which a program or computer fails to respond following the most recent mouse click or keyboard action.
A WDT contains a digital counter that counts down to zero at a constant speed from a preset number. The counter speed is kept constant by a clock circuit. If the counter reaches zero before the computer recovers, a signal is sent to designated circuits to perform the desired action