systemc data types 2pages

8/10/2019 SystemC Data Types 2pages

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KTH IL2452 System Design

Languages Lecture 5 1

Dr. Zhonghai Lu ()

School for ICT

KTH Royal Institute of Technology

2

C++ Basics SystemC

Introduction

and Get

Started

Concurrency

and Time

SystemC

Data Types

andDebugging

Modules

and

Processes

Channels

and

Interfaces

Transaction

Level

Modeling

SystemC

Summary

IL2452 System Design Languages


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3IL2452 System Design Languages

Aim

Understand SystemC data types and master how

to use them

Content

Overview of SystemC data types

Integer and vector types

Type conversion

Resolved signals (bus resolution)



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SystemC supports

Native C/C++ Types

SystemC Types: Data types oriented for hardware

modeling

SystemC Types

2 value (0,1) logic/logic vector

4 value (0,1,Z,X) logic/logic vector

Arbitrary sized integer (Signed/Unsigned) Fixed Point types (Templated/Untemplated)

Using namespace sc_dt


Type Description

Integer types

sc_int Signed Integer from 1-64 bits: sc_int

sc_uint Unsigned Integer from 1-64 bits

sc_bigint Arbitrary size signed integer: sc_bigint

sc_biguint Arbitrary size unsigned integer

Logic and Vector types

sc_logic Simple bit with 4 values(0/1/X/Z)

sc_bv Arbitrary size 2-values vector: sc_bv

sc_lv Arbitrary size 4-values vector

Fixed point types

sc_fixed templated signed fixed point

sc_ufixed templated unsigned fixed point

sc_fix untemplated signed fixed point

sc_ufix untemplated unsigned fixed point


sc_fix is the base class for sc_fixed. The size of an object of type

sc_fix is set when the object is created (i.e. by the constructor)

as opposed to sc_fixed where the size is set by the compiler

(using the template parameter).


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Four integer types: signed, unsigned, limited

width and big width.

sc_int, sc_uint

n 64

Regardless of the bit width n given by the template

parameter, internally stored with 64 bits of precision

sc_bigint, sc_biguint

No max. for n (unbounded)

Internally stored with as many as necessary to hold theresult

All integers are stored as binary numbers. Signed

numbers are stored in twos complement format.

sc_int, sc_lv, sc_bv7IL2452 System Design Languages

Operators Overloaded operators: bitwise, arithmetic, assignment,

equality, relationship

Bitwise operators (&(and), |(or), ^(xor), ~(not), )

Arithmetic operators ( +, -, *, /, %(modulo) )

Assignment (=) and compound assignment (+=, -=, *=, /=, %=,>>=,


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Assignment to any of the integer types causes

the value to be truncated to the given number of

bits without warning.

Precision of intermediate results determinedonly by the operands.

sc_uint a, b, c;

sc_uint d;

a = b = 15;

c = a + b;

d = a + b;

c=14

d=30

sc_uint j = 0x7fff ffff ffff ffff;

sc_biguint k;k = j * j;

k = sc_biguint (j) * j;

Truncated to 64 bits.

stored with arbitrary precision9IL2452 System Design Languages

sc_uint sc_int sc_int

Truncation!

problematic

Due to implicit type conversion,

it allows to mix the SystemC integer types sc_int

and sc_uint with C++ fundamental types int.

Any two SystemC types can be converted by

assignment operator =, which is overloaded. Signed/unsigned conversion loses sign without

warning.

sc_int a, b;

int d;

d = a & b;

a = b + d;

sc_int a;

sc_bigint B;

B = a;

a = B;

sc_int s;

sc_uint u;

s = -1;

u = s;

s = u;

u = 255

s = -1


Give an example of implicit

type conversion, which auser expects to occur?

Cannot add an sc_int to

an sc_logic.


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sc_logic is a 4-valued data type, similar to

VHDL type std_logic 4 values: 0, 1, X, Z

Initial value is X

Slower than bool

Vectors

sc_lv arbitrary length vector of sc_logic

sc_bv arbitrary length vector of bool Used for vectors longer than 64 bits where no need

arithmetic operators (shift is Ok).

Faster than sc_biguint

For vectors of 64 bits or less, sc_uint is faster and

more convenient.

Bitwise & | ^ ~

As sign ment = &= != ^=

Equality == !=

sc_logic a, b;

a = 1;

b = Z;

b = a & b;


Similar to std_logic in VHDL.

Concatenation means composing two or more vectors end-

to-end to create a single longer vector.

Two ways of concatenation

Overloaded comma operator

Function concat()

A concatenation can be used as an l-value, i.e., on the left

hand side of an assignment.

sc_uint a, b, d, e;

sc_unit c;

c = (a, b);

(d, e) = c;

11011100

11001101

a b

c

(a, b, c) = (c, b, a); concat(a, concat(b,c)) = concat(concat(c,b), a);12IL2452 System Design Languages


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To support bit select, the index operator [] is overloaded.

To support part select, use the method range() for sc_int,

sc_uint, sc_lv, sc_bv with 2 arguments.

For sc_int, sc_uint, the 1st argument the 2nd argument.

For sc_lv, sc_bv, if the first argument is less than the second, the

bits are read out of the vector in the reverse order.

Range() can be abbreviated by calling the overloaded operator()(int, int).

sc_int a;

bool b;

b = a[7]

a[6] = b;

a.range(7,4) = a.range(3,0);

sc_lv v = ZX10;cout


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Two SystemC data types can be

converted by assignment

(implicit type conversion). Thisdoes not hold for converting to

C++ types.

To convert from sc_bv,

sc_lv to int, need explicit

type conversion to_int().

Function to_string() convert to

a formatted text string.

The 1st argument gives therepresentation

The 2nd argument indicates

whether to include a prefix

showing the number base.

sc_lv lv = 0xff;

sc_bv bv = 0xff;sc_bigint si = 0xff;

int i;

i = lv.to_int( ); // return -1

i = bv.to_uint( ); //return 255

i = bi.to_long(); //return 255

cout


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Due to their compile-time overhead, fixed-

point types are omitted from the default

SystemC include file.

To enable fixed-point types, SC_INCLUDE_FX

must be defined prior to including the

SystemC header file.

IL2452 System Design Languages 17

#define SC_INCLUDE_FX

#include systemc.h

sc_fixed

}

Word length

Integer word length

value in [- 4, 3.75], precision 0.25

sc_fix var_1( 16, 4, SC_RND, SC_SAT);



var_1 = 0.5;

var_2 = 1.125;

var_3 = 0.7;

To model bus contention

(multiple drivers on a tri-

state bus wire), use a

different data type

sc_signal_resolved (not

sc_signal). When multiple processes

write to an instance of the

sc_signal_resolved, the

values are resolved

according to a resolution

table.

SC_CTOR(Driver){

SC_THREAD(p1);

SC_THREAD(p2);

}

sc_signal_resolved s;

void p1( ){

s.write(sc_logic(0));}

void p2( ){

s.write(SC_LOGIC_1);

wait(10, SC_NS);

s.write(SC_LOGIC_Z);}

}

Resolved 0 1 X Z

0 0 X X 0

1 X 1 X 1

X X X X X

Z 0 1 X Z



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sc_signal_resolved is a specialized channel of

sc_signal for type sc_logic

sc_signal_rv is a vector version of this

channel.

There are specialized ports, but they can

only be bound to resolved signals.

templateclass sc_signal_rv : public sc_signal< sc_lv > { }

class sc_signal_resolved : public sc_signal { }

sc_in< >

sc_inout< >sc_out< >

sc_in_resolved

sc_inout_resolvedsc_out_resolved

sc_in_rv< >

sc_inout_rv< >sc_out_rv< >


What if a user-defined data type passed over

using sc_signal?

Must define a default constructor

Must overload operators =, ==,


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Overview of SystemC data types: integer, vector, fixed

point types

Integer types

Note their differences with int

sc_int, sc_lv, sc_bv

Type conversion

Implicit conversion

Use explicit type cast Resolved signals (bus resolution)

sc_signal_resolved and sc_signal_rv

Need specialized ports to connect to resolved channels

User defined type passed over sc_signal21IL2452 System Design Languages

Try the type conversion, assignment and

truncation, bit/part select examples.

Try the signal resolution example.



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www.systemc.org

www.doulos.com

SystemC: From the Ground Up by D. C. Black,

J. Donovan, B. Bunton, and A. Keist.

System Design with SystemC by T. Grtker, S.

Liao, G. Martin, and S. Swan

Others


systemc data types 2pages

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