The finish of a grand tour of the language. Language Overview III The finish of a grand tour of the language. 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Elements Covered in III Reminder from I and II: Language overview lectures do not cover all aspects of the language. But they do cover a large portion of it. Concurrent Statements Sequential Statements Now ENTITIES, ARCHITECTURES, PACKAGES, PROCEDURES AND FUNCTIONS, OVERLOADING, LIBRARIES and the USE clause. 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU The ENTITY The basic concept of VHDL is that you have an interface and the function of the circuit within that interface. The interface (ENTITY) tells you what data and control arrives and how it arrives. The function (ARCHITECTURE) tells you how you operate on the data to produce results or respond to the inputs. 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU THE ENTITY entity_declaration::= entity identifier is entity_header entity_declarative_part [begin entity_statement_part] end [identifier]; entity_header::= [formal_generic_clause] [formal_port_clause] 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU The ENTITY formal_generic_clause::= generic (generic_list); formal_port_clause::= port (port_list); entity_declarative_part::= {entity_declarative_item} entity_declarative_item::= subprogram_declaration | subprogram_body | type_declaration | subtype_declaration | constant_declaration | signal_declaration | file_declaration | alias_declaration | attribute_declaration | attribute_specification | disconnect_specification | use_clause Items declared in the ENTITY have scope over all architectures of the entity 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU The ENTITY entity_statement_part::= entity_statement entity_statement::= concurrent_assertion_statement | passive_concurrent_procedure_call | passive_process_statement Passive means that the process or procedure call contains no signal assignment statements, nor calls to any other procedure which contains a signal assignment statement. Thus these passive procedure calls and processes can do monitoring only. They can use assertion statements to report status of the signals they are monitoring. 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU The ENTITY EXAMPLE entity LATCH is port (DIN: in WORD; DOUT: out WORD; LOAD, CLK : in BIT); constant SETUP : TIME := 12 ns; constant PulseWidth : TIME := 50 ns; use WORK.TimingMonitors.all; begin CheckTiming (SETUP,DIN,LOAD,CLK); end LATCH; 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU The Architecture This is the design unit that describes the function of the design. Possible styles are: Dataflow – using concurrent signal assignments = very, very close to the actual logic – a form of RTL RTL – register transfer level = just above dataflow and similar to RTL for a processor architecture Behavioral – algorithmic description of the functional behavior – very useful for reference models 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU The Architecture architecture identifier of entity_name is architecture_declarative_part begin architecture_statement_part end [identifier]; architecture_declarative_part::= {architecture_declarative_item} architecture_statement_part::= {concurrent_statement} 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU The Architecture architecture_declarative_item::= subprogram_declaration | subprogram_body | type_declaration | subtype_declaration | constant_declaration | signal_declaration | file_declaration | alias_declaration | component_declaration | attribute_declaration | attribute_specification | configuration_specification | disconnect_specification | use_clause 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Packages Packages provide a convenient way to declare commonly used declarations, functions, and procedures and make them available to many entities, architectures, and other packages. Packages are a design unit Consists of two parts The Package Declaration The Package Body 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Package Declaration package identifier is package_declarative_part end [identifier]; package_declarative_part::={package_declarative_item} package_declarative_item::= subprogram_declaration | type_declaration | subtype_declaration | constant_declaration | signal_declaration | file_declaration | alias_declaration | component_declaration | attribute_declaration | attribute_specification | disconnect_specification | use_clause 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Example of Package Declaration package TriState is type TRI is (‘0’,’1’,’Z’,’E’); function BitVal (value:TRI) return BIT; function TriVal (value:BIT) return TRI; end TriState; 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Package Body package body identifier is package_body_declarative_part end [identifier]; package_body_declarative_part::= {package_body_declarative_item} package_body_declarative_item::= subprogram_declaration | subprogram_body | type_declaration | subtype_declaration | constant_declaration | file_declaration | alias_declaration | use_clause 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Example package body TriState is function BitVal (value:TRI) return BIT is constant bits : BIT_VECTOR := (“0100”); begin return bits(TRI’POS(value)); end; function TriVal (value:BIT) return Tri is return Tri’Val(BIT’POS(value)); 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Notes on Packages Note: Only what is declared in the package declaration is visible outside the package!!! Items declared inside the package body are only visible inside the package body. 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Functions and Procedures Subprograms of the language Sequential statements are used within Functions and Procedures Declaration procedure designator [(formal_parameter_list)]; function designator [(formal_parameter_list)] return type_mark; 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Functions and Procedures The Body procedure designator [(formal_parameter_list)] is subprogram_declarative_part begin subprogram_statement_part end [designator]; function designator [(formal_parameter_list)] return type_mark is 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Functions and Procedures Functions must use a return statement as they must return a value function fg1 (w,x,g1 : IN BIT) return BIT; function fg1 (w,x,g1 : IN BIT) return BIT is BEGIN return (w and g1) or (not x and g1) or (w and not x); END; 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Other item of significance - OVERLOADING Overloading – You can overload any function or procedure in VHDL. EXAMPLE: procedure WRITE (F: inout TEXT; value:Integer); procedure WRITE (F: inout TEXT; value : String); These are two declarations for an overloaded procedure WRITE (if no mode is given on the arguments to a procedure or function the mode IN is presumed) USAGE DETERMINES WHICH VERSION OF THE PROCEDURE WILL BE USED USAGE write (MY_FILE, VAR); WRITE(sys_output, 12); WRITE(sys_error, “Actual output doesn’t match”); 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Overloaded Functions type MVL is (‘0’,’1’,’Z’,’X’); function “and” (L,R : MVL) return MVL; function “or” (L,R : MVL) return MVL; USAGE: signal Q,R,S : MVL Q <= ‘X’ or ‘1’; R <= S and Q; 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Libraries and Use Libraries provide a place to organize and store the design units – entities – architectures – package declarations – package bodies – that we have written and analyzed. Then to use those design units we need to make them visible with the current design unit so it can see, and thus use, them. 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU The Library clause Allows the use of design units from other libraries. When a library is created it has both an actual name and a logical name. The actual name is the file system name within the file system of the host computer system. The logical name is the name used within the VHDL system. LIBRARIES WORK and STD are visible to all design units. 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Library clause library logical_name_list; logical_name_list::=logical_name{,logical_name} This will make the logical_name(s) visible to the current design unit Declared just before the start of the design unit library WORK, MY_LIB; entity and_gate is PORT (A,B : in BIT; X : out BIT); end and_gate; 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Library Clause and Packages The library clause only makes the entities visible. It does not make any declarations within the package visible. Need to use a USE clause to make package declarations visible. USE clause: use library_name.package_name.items where items may be specific items or the reserved word all 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU Example of USE library ls7400; use ls7400.gates.all; entity new_thing is ….. where gates is a package with library ls7400. The all makes all declarations in package gates visible. ALL DESIGN UNITS ARE CONSIDERED TO HAVE library WORK, STD; use STD.STANDARD.ALL; 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU

Copyright 2006 - Joanne DeGroat, ECE, OSU A final note If you write a package and analyze it into library WORK, to use the declarations there you need to have a use clause. use WORK.TriState.TRI,WORK.TriState.BitVal; Or could have use WORK.TriState.ALL; This makes the type TRI and the function BitVal visible to the current design unit in addition to STD.STANDARD.ALL EXAMPLE SLIDE for type compatability 1/20/2007 - L8 Language Overview III Copyright 2006 - Joanne DeGroat, ECE, OSU