1. 16/11/2006DSD,USIT,GGSIPU1 Packages The primary purpose of a package is to encapsulate elements that can be shared (globally) among two or more design units. A package is a common storage area used to hold data to be shared among a number of entities Declaring data inside of a package allows the data to be referenced by other entities; thus data can be shared.

2. 16/11/2006DSD,USIT,GGSIPU2 Package (cont..) A package consists of two parts: –A package declaration section –A package body

3. 16/11/2006DSD,USIT,GGSIPU3 Package Declaration The package declaration section can contain the following declaration: –Subprogram declaration –Type, Subtype declaration –Constant, deferred constant –Component declaration –Attribute declaration –File declaration

4. 16/11/2006DSD,USIT,GGSIPU4 Package declaration (example) Package example is type nineval is (z0,z1,z2,r0,r1,r2,f0,f1,f2); type t_cluster is arary (0 to 15) or nineval; type t_clus_vec is array (natural range <>) of t_cluster; function resolve (s : t_clus_vec) return t_cluster; subtype t_wclus is resolve_cluster t_cluster; constant undriven : t_wclus; End example;

5. 16/11/2006DSD,USIT,GGSIPU5 Package body The package body can also contain the following declaration: –Subprogram declaration/body –Type, subtype declaration –Constant declaration –File declaration –Alias declaration –Use clause

6. 16/11/2006DSD,USIT,GGSIPU6 Package body (example) Package body cluspack is constant undriven : t_wclus:= (zx,zx); function resolve_cluster (s: t_clus_vec) return t_cluster is variable result : t_cluster; variable drive_const: integer; begin if s’length = 0 then return undriven end if;

7. 16/11/2006DSD,USIT,GGSIPU7 (cont..) For I in s’range loop if s(I) /= undriven then drive_count := drive_count + 1; if drive_count = 1 then result := a (I); else result : = undriven end if; End loop Return result;-- return value End resolve_cluster;-- end function End cluspack;-- end package

8. 16/11/2006DSD,USIT,GGSIPU8 Subprograms Subprograms consist of –Procedure –Function

9. 16/11/2006DSD,USIT,GGSIPU9 Subprogram properties Similar to PROCESS statements IF, CASE, and LOOP, WAIT is not allowed. Fundamental difference at the level of application. Process is intended for immediate use in the main code, the others are intended mainly for Library allocation, I.e. their purpose is to store commonly used pieces of code, so they can be reused or shared by other projects. If, desired, a Function or Procedure can also be installed in the main code itself.

10. 16/11/2006DSD,USIT,GGSIPU10 Procedure and Function A procedure can return more than one argument. A procedure can have input parameters, output parameters and inout parameters A function always returns just one. All parameters are input parameters E.g. data type conversions, logical operations, arithmetic computations, new operator and attributes Signal declaration and component instantiation is not allowed.

11. 16/11/2006DSD,USIT,GGSIPU11 Function syntax To construct and use of a function, two parts are necessary: –The function body and –A call to the function

12. 16/11/2006DSD,USIT,GGSIPU12 Function body FUNCTION function_name [ ] RETURN data_type is [declaration] Begin [sequential statements] END function_name;

13. 16/11/2006DSD,USIT,GGSIPU13 Function body (cont..) = [CONSTANT] constant_name: constant_type; or = SIGNAL signal_name:signal_type; VARIABLES are not allowed. There can be any type of synthesizable data types. No range specification should be included (e.g. do not enter range when using INTEGER or TO/Down to when using std_logic_vector) There is only one return value, whose type is specified by data_type.

14. 16/11/2006DSD,USIT,GGSIPU14 Example of function body FUNCTION f1 (a,b : integer; signal c : std_logic_vector ) return BOOLEAN is Begin (sequential statements) END f1;

15. 16/11/2006DSD,USIT,GGSIPU15 Function call A function is called as par of an expression. The expression can obviously appear by itself or associated to a statement (either concurrent or sequential). Example of function calls: X <= conv_integer (a); -- converts a to an integer Y <= maximum (a,b); --returns the largest of a and b; If x > maximum (a,b); --compares x to the largest of a,b

16. 16/11/2006DSD,USIT,GGSIPU16 Function Location Function/Procedure location PackageMain code (+Package body) ArchitectureEntity Library

17. 16/11/2006DSD,USIT,GGSIPU17 Function Use library ieee; Use ieee.std_logic_1164.all; package num_type is type log8 is array (0 to 7) of std_logic; end num_type;

18. 16/11/2006DSD,USIT,GGSIPU18 Use library ieee; Use ieee.std_logic_1164.all; Use work.num_type.all; Entity convert is port (i1 : in log8; o1 : out integer); End convert;

19. 16/11/2006DSD,USIT,GGSIPU19 Architecture behave of convert is function vector_to_int (s : log8) return integer is variable result : integer := 0; begin for I in 0 to 7 loop result : = result * 2: if s(I) = ‘1’ then result := result + 1; end if; end loop; return result; end vector_to_int; Begin o1 <= vector_to_int(i1); End behave;

20. 16/11/2006DSD,USIT,GGSIPU20 Conversion Function Conversion Function are used to convert an object of one type to another. They are used in component instantiation statement to allow mapping of signals and ports of different types.

21. 16/11/2006DSD,USIT,GGSIPU21 Conversion function (example) Function conversion4val (s: fourval) return fourvalue is Begin case s is when x => return ‘x’; when L => return ‘0’; when H => return ‘1’ when z => return ‘z’; end case; End convert4val;

22. 16/11/2006DSD,USIT,GGSIPU22 Resolution Function A resolution function is used to return the value of a signal when the signal is driven by multiple drivers. A resolution function consists of a function that is called whenever one of the drivers for the signal has an event occur on it. The resolution function is executed and returns a single value from all of the driver values; this value is the new value of the signal.

23. 16/11/2006DSD,USIT,GGSIPU23 Operator Overloading When a standard operator symbol is made to behave differently based on the type of its operands, the operator is said to be overloaded. Function bodies are written to define the behavior of overloaded opertors. The number of parameters in such a function must match in cardinality with that of the predefined operator.

24. 16/11/2006DSD,USIT,GGSIPU24 Procedure A procedure is very similar to a function. A procedure can return more than one value Two parts are required to construct and use a procedure –Procedure body –Procedure call

25. 16/11/2006DSD,USIT,GGSIPU25 Procedure body Procedure procedure_name [ ] is [declarations] Begin (sequential statements) End procedure_name;

26. 16/11/2006DSD,USIT,GGSIPU26 Procedure (example) Procedure my_procedure( a : in std_logic; signal b,c : in std_logic; signal x : out std_logic_vector(7 downto 0); signal y : inout integer range 0 to 99) is Begin ------ End my_procedure;

27. 16/11/2006DSD,USIT,GGSIPU27 = [CONSTANT] constant_name: mode type = SIGNAL signal_name: mode type; or = VARIABLE variable_name : mode type A procedure can have any number of IN,OUT or INOUT parameters, Which can be SIGNALS, VARIABLES, or CONSTANTS.

28. 16/11/2006DSD,USIT,GGSIPU28 Procedure call Procedure call is a statement on its own. It can appear by itself or associated to a statement (either concurrent or sequential) Ex. –Compute_min_max(in1,in2,out1,out2)

29. 16/11/2006DSD,USIT,GGSIPU29 Procedure Location The typical locations of a procedure are the same as those of a function.