System on Chip and Embedded Systems

8/9/2019 System on Chip and Embedded Systems

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Mr. A. B. Shinde

Assistant Professor,

Electronics Engineering,

PVPIT, Budhgaon

[email protected]

mailto:[email protected]:[email protected]


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System-on-a-chip or system on chip (SoC or SOC) refers to

integrating all components of a computer or other electronicsystem into a single integrated circuit (chip).

It may contain digital, analog, mixed-signal, and often radio-frequency functions – all on one.

Microcontrollers typically have under 100K of RAM are single-chip-systems;

whereas the term SoC is typically used with more powerfulprocessors, capable of running software such as Windows or Linux, which need external memory chips (flash, RAM) to beuseful, and which are used with various external peripherals.

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Many interesting systems are too complex to fit on just one chip

built with a process optimized for just one of the system's tasks.

When it is not feasible to construct an SoC for a particular application, an alternative is a system in package (SiP)comprising a number of chips in a single package.

In large volumes, SoC is believed to be more cost effectivethan SiP, because its packaging is simpler.

The SoC chip includes processors and numerous digitalperipherals, and comes in a ball grid package with lower andupper connections.

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One microcontroller, microprocessor or DSP core(s). Some

SoCs – called multiprocessor System-on-Chip (MPSoC) –include more than one processor core.

1. Memory blocks including a selection of ROM, RAM, EEPROMand Flash.

2. Timing sources including oscillators and phase-locked loops.

3. Peripherals including counter-timers, real-time timers and

power-on reset generators.

4. External interfaces including industry standards such as USB,FireWire, Ethernet, USART, SPI.

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Analog interfaces including ADCs and DACs.

Voltage regulators and power management circuits.

These blocks are connected by either a proprietary or industry-

standard bus such as the AMBA bus from ARM.

DMA controllers route data directly between externalinterfaces and memory, by-passing the processor core andthereby increasing the data 6 throughput of the SoC

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Power SupplyCLKCLK

CLKcustom

IF-logic

SDRAM SDRAMSRAM SRAMSRAM

Memory

Controller

UARTL

C

Display

Controller

Interrupt

Controller

Timer

Audio

Codec

CPU(uP / DSP) Co-

Proc.

GP I/O

Address

Decode

Unit

Ethernet

MAC

Traditional Embedded System

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FPGACLKCLK

CLKcustom

IF-logic


Memory

Controller

UART

Display

Controller

Timer

Power Supply

L

C

Audio

Codec

CPU(uP / DSP) Co-

Proc.

GP I/O

Address

Decode

Unit

Ethernet

MAC

Interrupt

Controller

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Power Supply


L

C

Audio

Codec EPROM

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A SoC consists of both the hardware described above, and the

software controlling the microcontroller, microprocessor or DSPcores, peripherals and interfaces.

The design flow for a SoC aims to develop this hardware andsoftware in parallel.

Most SoCs are developed from pre-qualified hardware blocks,together with the software drivers that control their operation.

The hardware blocks are put together using CAD tools; thesoftware modules are integrated using a software-developmentenvironment.

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A key step in the design flow is: The hardware is mapped onto

an FPGA that mimics the behavior of the SoC, and the softwaremodules are loaded into the memory.

Once programmed, the emulation platform enables the hardwareand software of the SoC to be tested and debugged at close to

its full operational speed.

After emulation the hardware of the SoC follows the place androute phase of the design of an integrated circuit before it isfabricated.

Chips are verified for logical correctness before being sent tofoundry. This process is called functional verification.

Verilog and VHDL are typical hardware description languagesused for verification.

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Microcontroller:

A microcontroller is a processor that has its program and datamemory built in.

These chips are intended for small embedded controlapplications, so leaving the pins for I/O and not requiring aexternal memory bus.

Some microcontrollers have as little as 6 pins, and can douseful things.

In contrast, general purpose computing processor (GPP) isintended for a large computations, such can have 100s of pinsin a array and require extensive external circuitry.

In general a microcontroller is taken as being an embeddeddevice which is internally programmed to perform a specifictask.

There is minimal user interaction and little or no flexibility.

A microcontroller is typically fairly low powered with only smallamounts of memory and ROM (flash). 13


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SoC:

Conversely a System-on-Chip is the other end of the spectrum. It is more geared towards complete flexibility and user

interaction.

It often includes things like IO drivers for bigger hardware, andeven sometimes a graphics adapter.

A System-on-Chip is more like a complete computer system, ona single chip.

System on Chip, is a less well defined term.

Cyprus calls some of their parts PSOC (Programmable System

on Chip). These are basically a microcontroller with small FPGA on the

same chip.

Instead of having built in peripherals, you can make whatever you want within the available resources of the FPGA.

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An embedded system is a

special-purpose computer system designed to perform oneor a few dedicated functions,often with real- time computingconstraints.

It is usually embedded as partof a complete device includinghardware and mechanicalparts. In contrast, a general-purpose computer, such as a

personal computer, can domany different tasks dependingon programming.

Embedded systems control

many of the common devices inuse today.

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Physically, embedded systems range from portable devices

such as digital watches and MP4 players, to large stationaryinstallations like traffic lights, factory controllers, or the systemscontrolling nuclear power plants.

Complexity varies from low, with a single

microcontroller chip, to very high with multiple units, peripheralsand networks mounted inside a large chassis or enclosure.

In general, "embedded system" is not an exactly defined term, asmany systems have some element of programmability.

For example, Handheld computers share some elements withembedded systems — such as the operating systems andmicroprocessors which power them — but are not trulyembedded systems, because they allow different applicationsto be loaded and peripherals to be connected.

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INTRO TO

EMBEDDED S YSTEM DESIGN


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A Microcontroller is essentially a small and self sufficient

computer on a chip, used to control devices

It has all the memory and I/O it needs on board

Is not expandable – no external bus interface

Characteristics of a Microcontroller

Low cost

Low speed, on the order of 10 KHz – 20 MHz

Low Power, extremely low power in sleep mode

Small architecture, usually an 8-bit architecture

Small memory size, but usually enough for the type of application it is intended for. Onboard Flash.

Limited I/O, but again, enough for the type of application

intended for. 19


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A Microprocessor is fundamentally a collection of on/off switches

laid out over silicon in order to perform computations

Characteristics of a Microprocessor

High cost

High speed, on the order of 100 MHz – 4 GHz

High Power consumption, lots of heat

Large architecture, 32-bit, and recently 64-bit architecture

Large memory size, onboard flash and cache, with an externalbus interface for greater memory usage

Lots of I/O and peripherals, though Microprocessors tend to beshort on General purpose I/O

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Harvard Architecture refers to a memory structure where the

processor is connected to two different memory banks via twosets of buses

This is to provide the processor with two distinct data paths, onefor instruction and one for data

Through this scheme, the CPU can read both an instructionand data from the respective memory banks at the same time

This inherent independence increases the throughput of themachine by enabling it to always pre-fetch the next instruction

The cost of such a system is complexity in hardware commonlyused in DSPs

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A Von-Neumann Machine, in contrast to the Harvard Architecture

provides one data path (bus) for both instruction and data

As a result, the CPU can either be fetching an instructionfrom memory, or read/writing data to it

Other than less complexity of hardware, it allows for using asingle, sequential memory.

Today‘s processing speeds vastly outpace memory access

times, and we employ a very fast but small amount of memory(cache) local to the processor

Modern processors employ a Harvard Architecture to read fromtwo instruction and data caches, when at the same time using a

Von-Neumann Architecture to access external memory 22


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Although numbers are always displayed in the same way,

they are not stored in the same way in memory

Big-Endian machines store the most significant byte of data inthe lowest memory address

Little-Endian machines on the other hand, store the leastsignificant byte of data in the lowest memory address

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The Intel family of Microprocessors and processors from Digital

Equipment Corporation use Little- Endian mode

Whereas Architectures from Sun, IBM, and Motorola areBig-Endian

Architectures such as PowerPC, MIPS, and Intel‘s IA- 64 are

Big-Endian, supporting either mode

Unfortunately both methods are in prevalent use today, and

neither method is superior to the other

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The Program Counter is a 16 or 32 bit register which contains

the address of the next instruction to be executed

The PC automatically increments to the next sequential memorylocation every time an instruction is fetched

Branch, jump, and interrupt operations load the ProgramCounter with an address other than the next sequential location

During reset, the PC is loaded from a pre-defined memory

location to signify the starting address of the code

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The significance of the reset vector is that it points the processor

to the memory address which contains the firmware‘s firstinstruction

Without the Reset Vector, the processor would not know where tobegin execution

Upon reset, the processor loads the Program Counter (PC) withthe reset vector value from a pre-defined memory location

On CPU08 architecture, this is at location$FFFE:$FFFF

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The Stack Pointer (SP), much like the reset vector, is required at

boot time for many processors

Some processors, in particular the 8-bit microcontrollersautomatically provide the stack pointer by resetting it to apredefined value

On a higher end processor, the stack pointer is usually read froma non-volatile memory location, much like the reset vector

For example on a Cold-Fire microprocessor, the first sixteenbytes of memory location must be programmed as follows:

0x00000000: Reset Vector 0x00000008: Stack Pointer

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The Computer Operating Properly (COP) module is a component

of modern processors which provides a mechanism to helpsoftware recover from runaway code

The COP, also known as the Watchdog Timer, is a free runningcounter that generates a reset if it runs up to a pre-defined value

and overflows

In order to prevent a watchdog reset, the user code must clear the COP counter periodically.

COP can be disabled through register settings, and eventhough this is not good practice for final firmware release, it is aprudent strategy through the course of debug

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Embedded Systems, unlike a PC, never ―exit an application

They idle through an Infinite Loop waiting for an event to happenin the form of an interrupt, or a pre-scheduled task

In order to save power, some processors enter special sleepor wait modes instead of idling through an Infinite Loop, butthey will come out of this mode upon either a timer or anExternal Interrupt

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Interrupts are mostly hardware mechanisms which tell the

program an event has occurred

They happen at any time, and are therefore asynchronous toprogram flow

They require special handling by the processor, and areultimately handled by a corresponding Interrupt Service Routine(ISR)

Need to be handled quickly.

It takes too much time for servicing an interrupt, and you maymiss another interrupt.

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Proposal

Definition Technology Selection

Budgeting (Time, Human, Financial)

Material and Development tool purchase

Schematic Capture & PCB board design Firmware Development & Debug

Hardware Manufacturing

Testing

Certification

Firmware Release

Documentation

Ongoing Support

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The purpose of the design cycle is to remind and guide the

developer to step within a framework proven to keep you ontrack and on budget.

There are numerous design cycle methodologies, of which thefollowing are most popular

The Waterfall Model

Top-down versus Bottom-up

Spiral Model

GANTT charts

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THE WATERFALL MODEL

Waterfall is a software development model in which developmentis seen flowing steadily through the phases of

Requirement Analysis

Design

Implementation

Testing

Integration

Maintenance

Advantages are good progress tracking due to clear milestones

Disadvantages are its inflexibility, by making it difficult torespond to changing customer needs / market conditions

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TOP-DOWN VERSUS BOTTOM-UP

The Top-Down Model analyses the overall functionality of asystem, without going into details

Each successive iteration of this process then designsindividual pieces of the system in greater detail

The Bottom-Up Model in contrast defines the individual piecesof the system in great detail

These individual components are then interfaced together toform a larger system

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THE SPIRAL MODEL

Modern software design practices such as the Spiral Modelemploy both top-down and bottom- up techniques

Widely used in the industry today

For a GUI application, for example, the Spiral Model wouldcontend that

You first start off with a rough-sketch of user interface(simple buttons & icons)

Make the underlying application work

Only then start adding features and in a final stage neat up thebuttons & icons

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GANTT CHART

GANTT Chart is simply a type of bar chart which shows theinterrelationships of how projects and schedules progress over time

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Metrics to consider in designing an Embedded System

Unit Cost: Can be a combination of cost tomanufacture hardware + licensing fees

NRE Costs: Non Recurring Engineering costs

Size: The physical dimensions of the system

Power Consumption: Battery, power supply, wattage, currentconsumption, etc.

Performance: The throughput of the system, its responsetime, and computation power

Safety, fault-tolerance, field-upgradeability, ruggedness,

maintenance, ease of use, ease of installation, etc. etc. 37


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Problem Statement

allowing a chamber temperature set-point to be entered,

displaying both set-point and actual temperatures, and

tracking step changes in set-point temperature with acceptable

rise time, steady-state error, and overshoot.

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Temperature controller specifications

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Temperature controller hardware block diagram

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Temperature controller hardware The microcontroller, a Motorola MC68HC705B16 (6805 for

short), is the heart of the system.

It accepts inputs from a simple four-key keypad e.g. set-pointtemperature, and it displays both set-point and measured

chamber temperatures using two-digit seven-segment LEDdisplays controlled by a display driver.

All these inputs and outputs are accommodated by parallelports on the 6805.

Chamber temperature is sensed using a pre-calibrated

thermistor and input via one of the 6805’s analog-to-digitalinputs.

Finally, a pulse-width modulation (PWM) output on the 6805 isused to drive a relay which switches line power to the resistiveheater off and on.

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Schematic of

microcontroller

board

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Figure shows a schematic of the electronics and their interfacingto the 6805.

The keypad, a Storm 3K041103, has four keys which areinterfaced to pins PAO- PA3 of Port A, configured as inputs.

One key functions as a mode switch. Two modes are supported: set mode and run mode.

In set mode two of the other keys are used to specify the set-point temperature: one increments it and one decrements.

The fourth key is unused at present.

The LED displays are driven by a Harris Semiconductor ICM7212display driver interfaced to pins PB0-PB6 of Port B, configured asoutputs.

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The temperature-sensing thermistor drives, through a voltagedivider, pin AN0 (one of eight analog inputs). Finally, pin PLMA(one of two PWM outputs) drives the heater relay.

Software on the 6805 implements the temperature control

algorithm, maintains the temperature displays, and alters the set-point in response to keypad inputs.

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The design of a SoC has similar goals as an embedded design.

The designed system will be used in a well-specifiedenvironment, and has to fulfill strict requirements.

Some requirements are clearly defined by the application like the

functional requirements of an algorithm, e.g. the decoding of anMPEG 1 Layer 3 data stream, which covers certain qualityrestrictions.

The environment poses other requirements: e.g. minimizing thecost, footprint, or power consumption. However due to theflexibility of a SoC design, achieving the set goals, involvesanalyzing a multi dimensional design space.

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The degrees of freedom stem from the process element types

and characteristics, their allocation, the mapping of functional elements to the process elements, their interconnectionwith busses and their scheduling.

A SoC design has to deal with a wide range: it starts with a

functional description on system level, where major functionblocks are defined and no timing information is given.

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The goal of SoC design paradigm is to manage the immense sizeof design decisions in the hardware software co-design.

This is only possible by above well-defined flow of design steps52


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System on Chip and Embedded Systems