DSP Processors

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DSP ProcessorsDigital Signal Processors

4\3\2012

Group#13

DSP processors ◦ Architecture◦ Data handling◦ Program flow ◦ Programming ◦ Applications

Outlines


Outlines

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A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing. ◦ DSP is the application of mathematical operations to digitally represent

signals.

The source of these signals can be

◦ Audio

◦ Image

DSP processors

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Digital signal processing enjoys several advantages over analog signal processing:

◦ DSP systems are able to accomplish tasks inexpensively that would be difficult or even impossible using analog electronics. (Examples of such applications include speech synthesis and speech recognition).

◦ Insensitivity to environment.◦ Insensitivity to component tolerances. ◦ Repeatable behavior.◦ Re-programmability.◦ Size.

DSP processors

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◦ Arithmetic and Multiplication (add, subtract, increment, decrement, negate, round,

absolute value) and multiplication. With the exception of the Texas Instruments TMS320Clx

processor provide multiply-accumulate instructions as well.

◦ Logic Operations and, or, exclusive-or, and not.

◦ Shifting Arithmetic (left and right). Logical (left and right).

Instruction types

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◦ Rotation Left. Right.

◦ Comparison Most processors provide a set of status bits (ex: zero-Bit,

minus Bit and overflow Bit) that provide information about the results of arithmetic operations.

used in conditional branches or conditional execution instructions.

◦ Looping

◦ Subroutine Calls may be called jump-to-subroutine instructions.

Instruction types(Cont.)

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◦ Branching jump or got o instructions on some processors.


ConditionalUn-

conditional

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◦ Branching (cont.)


DelayedMulticycle


Outlines

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Instruction sets

◦ A basic DSP processor supports RISC (Reduce Instruction Set Computers) and CISC (Complex Instruction Set Computers) instructions.

◦ Single instruction, multiple data (SIMD) ◦ Instruction-level parallelism (ILP)

Architecture

Single instruction, multiple data (SIMD) Single instruction, multiple data describes

computers with multiple processing elements that perform the same operation on multiple data simultaneously.

Architecture (cont.)

Instruction-level parallelism (ILP)◦ Instruction-level parallelism (ILP) is a measure of how

many of the operations in a computer program can be performed simultaneously.

◦ Ex: 1. e = a + b 2. f = c + d independent 3. g = e * f

◦ ILP allows the compiler and the processor to overlap the execution of multiple instructions or even to change the order in instructions

Architecture (cont.)

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◦ Transferring information to and from memory includes data, such as samples from the input signal and the filter coefficients, as well as program instructions, the binary codes that go into the program sequencer.

◦ Ex.

Architecture of the Digital Signal Processor

a b×a

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There are mainly three types of architectures employed for the processors:

1. Von Neumann architecture2. Harvard architecture3. Super Harvard Architecture

Architecture of the DSP(cont.)

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contains a single memory and a single bus for transferring data into and out of the central processing unit (CPU).

For example,

1-Von Neumann architecture

Memory (instruction and

data)CPU

add. bus

data bus

a b×a

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• Advantages:• This type of architecture is cheap, and • Simple to use because the programmer can place

instructions or data anywhere throughout the available memory.

• Disadvantages:• Von Neumann computers spend a lot of time moving

data to and from the memory, and his slows the computer.

1-Von Neumann architecture(cont.)

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Separate memories for data and program instructions, with separate buses for each.

• For example,

2- Harvard architecture

Program Memory

(instruction only)

CPUData

Memory (data only)

PM add. bus

PM data bus

DM add. bus

DM data bus

a b×a

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• Advantages:• Since the buses operate independently, program

instructions and data can be fetched at the same time, improving the speed over the single bus design.

• Disadvantages:• data memory bus is busier than the program memory

bus.

2- Harvard architecture(cont.)

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Improves upon the Harvard design by adding an instruction cache and dedicated I/O controller.

• For example,

3- Super Harvard Architecture

a b×a

Program Memory (instruction and secondary data)

CPU Data Memory

(data only)

I/O Controller

Instruction Cache

PM add. bus

PM data bus

DM add. bus

DM data bus

Data

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• Advantages:• the instruction cache improves the performance of the

Harvard architecture.• I/O controller connected to data memory this dedicated

hardware allows the data streams to be transferred directly into memory without having to pass through the CPU's registers.

• Disadvantages:• If we were executing random instructions, this situation

would be no better at all.

3- Super Harvard Architecture (cont.)

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Now let's look inside the CPU

Architecture of the DSP(Cont.)

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At the top of the diagram are two blocks labeled Data Address Generator (DAG), one for each of the two memories.

◦ These control the addresses sent to the program and data memories, specifying where the information is to be read from or written to.


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The data register section : contains16 general purpose registers of 40 bits each. ◦ These can hold intermediate calculations, ◦ prepare data for the math processor, ◦ serve as a buffer for data transfer, ◦ hold flags for program control.


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The math processing is broken into three sections,◦ a multiplier (MAC), ◦ an arithmetic logic unit (ALU), and ◦ a shifter.



Outlines

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DSP processors fall into two major categories based on the way they represent numerical values and implement numerical operations internally.

Data handling

Fixed PointFloating Point

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Floating point◦ Floating point processors primarily represent numbers in

floating point format.

◦ Advantages: Easier to develop code.. The large dynamic range available means that dynamic range

limitations can be practically ignored in a design.

◦ Disadvantages: More expensive because they implement more functionality

(complexity )in silicon and have wider buses (32 bit).

Data handling (Cont.)

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Fixed point◦ Fixed point processors represent and manipulate numbers

as integers.

◦ Advantages: lower cost and higher speed

◦ Disadvantages: Added design effort for algorithm implementation analysis, and

data and Coefficient scaling to avoid accumulator overflow (16-20-24 bit).


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Let’s take an example:

FIR filters (Finite Impulse Response)

y[n]=b0 x[n] + b1 x[n-1] + b2 x[n-2] + ……. + bN x[n-N]

Structurally, FIR filters consist of just two things: ◦ a sample delay line and ◦ a set of coefficients.


RoundOr

Truncate(at fixed point)


Outlines

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Pipelined

Hardware-controlled looping

Program flow

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Pipelined


Program flow

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A pipeline is a set of data processing elements connected in series, so that the output of one element is the input of the next one.

Instruction pipelines, used in processors to allow overlapping execution of multiple instructions.

Pipelined

Fetch

Decode

Execute

Fetch ‘A’

• 2nd CLK Cycle

Fetch ‘B’

Decode ‘A’

• 3rd CLK Cycle

Fetch ‘C’

Execute‘A’

Decode ‘B’

• 1st CLK Cycle

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1st Approach◦ Each clock cycle = 20ns◦ One instruction = 80 ns◦ each stage of instruction execution is idle 75 % of the

time.

Pipelined (cont.)

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2nd Approach◦ One instruction is now completed every clock cycle

(every 20 ns)

Pipelined (cont.)

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Pipelined


Program flow

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DSP algorithms frequently involve the repetitive execution of a small number of instructions (ex: FIR and IIR filters, FFTs and matrix multiplication)

DSP processors have evolved to include features to efficiently handle this sort of repeated execution.


MOV #16,B LOOP : MAC (R0)+,(R4+),A DEC B JNE LOOP

RPT #16 MAC (R0)+,(R4+),A


Outlines

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Most DSPs are programmed in special versions of C.

DSP vendors will almost always provide support for C++ programming, but it is not very popular in the DSP software industry.

Some DSP software programmers will resort to assembly programming for DSPs.

Programming


Outlines

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Digital cameras.

Digital radios.

High-resolution printers.

Satellites.

Applications

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Documents

DSP Processors