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Chapter 6 Subprograms & Packages

Subprogram declaration Subprogram body Package declaration Package body Resolution function. Subprogram overloading Subprogram return values and types Type casting and type qualification Exercises. Chapter 6 Subprograms & Packages. Subprogram declaration. Subprogram_declaration::=

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Chapter 6 Subprograms & Packages

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  1. Subprogram declaration Subprogram body Package declaration Package body Resolution function Subprogram overloading Subprogram return values and types Type casting and type qualification Exercises Chapter 6 Subprograms & Packages EE514

  2. Subprogram declaration Subprogram_declaration::= procedure name[(interface_list)]| function name[(interface_list)] return type-mark; VHDL Syntax (IEEE Std 1076-1987) check : http://mikro.e-technik.uni-ulm.de/vhdl/vhdl87_syntax.html EE514

  3. Subprogram declaration interface_list::=interface_declaration{;interface_declaration} interface_declaration::= [constant] identifier_list:[in] subtype_indication [:=static_expression] [signal] identifier_list:[mode] subtype_indication[bus] [:=static_expression]| [variable] identifier_list:[mode]subtype_indication [:=static_expression] mode::=in|out|inout|buffer|linkage EE514

  4. Subprogram declaration EE514

  5. Subprogram body Subprogram_body::= subprogram_declaration is subprogram_declarative_part begin sequential statements end [procedure identifier or function designator]; EE514

  6. entity FACT is end FACT; architecture RTL of FACT is function FACTORIAL (constant N : in integer) return integer is begin if (N = 1) then return 1; elsif (N > 1) and (N < 10) then return N * FACTORIAL (N - 1); else assert FALSE report "0 < N < 10 is not true" severity NOTE; return 0; end if; end FACTORIAL; signal NUM, RESULT : integer; begin RESULT <= FACTORIAL (NUM); end RTL; Subprogram body EE514

  7. EE514

  8. Package declaration Package_declaration::= package identifier is package_declarative_part end[identifier]; Package declarative part may consist of subprogram declaration, type, subtype, constant, signal, file, alias, component, and attribute declarations, attribute and disconnect specification, and use clause. EE514

  9. Package declaration package_body::= package body identifier is package_body_declarative_part end[identifier]; Package body defines bodies of subprograms or values of deferred constants declared in the package declaration EE514

  10. Package declaration package PACK1164 is type std_ulogic is ( 'U', -- Uninitialized 'X', -- Forcing Unknown '0', -- Forcing 0 '1', -- Forcing 1 'Z', -- High Impedance 'W', -- Weak Unknown 'L', -- Weak 0 'H', -- Weak 1 '-'); -- Don't care type std_ulogic_vector is array ( NATURAL RANGE <> ) of std_ulogic; function resolved ( s : std_ulogic_vector ) RETURN std_ulogic; subtype UX01 is resolvedstd_ulogic RANGE 'U' TO '1'; subtype std_logic is resolved std_ulogic; type std_logic_vector is array ( NATURAL RANGE <>) of std_logic; function "and" ( l : std_ulogic; r : std_ulogic ) RETURN UX01; function "and" ( l, r : std_logic_vector ) RETURN std_logic_vector; function "and" ( l, r : std_ulogic_vector ) RETURN std_ulogic_vector; end PACK1164; EE514

  11. Resolution function library IEEE; use IEEE.std_logic_1164.all; entity DRIVE2 is port ( A, B, A_ENn, B_ENn : in std_logic; Y : out std_logic); end DRIVE2; architecture RTL of DRIVE2 is begin Y <= A when A_ENn = '0' else 'Z'; Y <= B when B_ENn = '0' else 'Z'; end RTL; EE514

  12. Resolution function ( 'U', 'X', 'X', 'X', 'X', 'X', 'X', 'X', 'X' ) -- | - | ); function resolved ( s : std_ulogic_vector ) RETURN std_ulogic IS variable result : std_ulogic := 'Z'; -- weakest state default begin if (s'LENGTH = 1) then RETURN s(s'LOW); else for i in s'RANGE loop result := resolution_table(result, s(i)); end loop; end if; RETURN result; end resolved; package body PACK1164 is type stdlogic_1d is array (std_ulogic) of std_ulogic; type stdlogic_table is array (std_ulogic, std_ulogic) of std_ulogic; constant resolution_table : stdlogic_table := ( -- --------------------------------------------------------- -- | U X 0 1 Z W L H - | | -- --------------------------------------------------------- ( 'U', 'U', 'U', 'U', 'U', 'U', 'U', 'U', 'U' ), -- | U | ( 'U', 'X', 'X', 'X', 'X', 'X', 'X', 'X', 'X' ), -- | X | ( 'U', 'X', '0', 'X', '0', '0', '0', '0', 'X' ), -- | 0 | ( 'U', 'X', 'X', '1', '1', '1', '1', '1', 'X' ), -- | 1 | ( 'U', 'X', '0', '1', 'Z', 'W', 'L', 'H', 'X' ), -- | Z | ( 'U', 'X', '0', '1', 'W', 'W', 'W', 'W', 'X' ), -- | W | ( 'U', 'X', '0', '1', 'L', 'W', 'L', 'W', 'X' ), -- | L | ( 'U', 'X', '0', '1', 'H', 'W', 'W', 'H', 'X' ), -- | H | EE514

  13. A A_ENn B B_ENn Y ---H--- --------L-------- Z Resolution function architecture RTL of DRIVE2 is begin Y <= A when A_ENn = '0' else 'Z'; Y <= B when B_ENn = '0' else 'Z'; end RTL; Notice that initial drivers for Y are Z EE514

  14. Subprogram overloading constant and_table : stdlogic_table := ( -- ---------------------------------------------------- -- | U X 0 1 Z W L H - | | -- ---------------------------------------------------- ( 'U', 'U', '0', 'U', 'U', 'U', '0', 'U', 'U' ), -- | U | ( 'U', 'X', '0', 'X', 'X', 'X', '0', 'X', 'X' ), -- | X | ( '0', '0', '0', '0', '0', '0', '0', '0', '0' ), -- | 0 | ( 'U', 'X', '0', '1', 'X', 'X', '0', '1', 'X' ), -- | 1 | ( 'U', 'X', '0', 'X', 'X', 'X', '0', 'X', 'X' ), -- | Z | ( 'U', 'X', '0', 'X', 'X', 'X', '0', 'X', 'X' ), -- | W | ( '0', '0', '0', '0', '0', '0', '0', '0', '0' ), -- | L | ( 'U', 'X', '0', '1', 'X', 'X', '0', '1', 'X' ), -- | H | ( 'U', 'X', '0', 'X', 'X', 'X', '0', 'X', 'X' ) -- | - | ); function "and" ( l : std_ulogic; r : std_ulogic ) RETURN UX01 is begin RETURN (and_table(l, r)); end "and"; EE514

  15. Subprogram overloading Aliases are used to normalize array bonds function "and" (l,r : std_logic_vector ) RETURN std_logic_vector is alias lv : std_logic_vector ( 1 TO l'LENGTH ) is l; alias rv : std_logic_vector ( 1 TO r'LENGTH ) is r; variable result : std_logic_vector ( 1 TO l'LENGTH ); begin if ( l'LENGTH /= r'LENGTH ) then assert FALSE report "arguments of 'and' operator are not of the same length" severity FAILURE; else for i in result'RANGE loop result(i) := and_table (lv(i), rv(i)); end loop; end if; RETURN result; end "and"; function "and" ( l,r : std_ulogic_vector ) RETURNstd_ulogic_vector is alias lv : std_ulogic_vector ( 1 TO l'LENGTH ) is l; alias rv : std_ulogic_vector ( 1 TO r'LENGTH ) is r; variable result : std_ulogic_vector ( 1 TO l'LENGTH ); begin if ( l'LENGTH /= r'LENGTH ) then assert FALSE repor "arguments of 'and' operator are not of the same length" severity FAILURE; else for i in result'RANGE loop result(i) := and_table (lv(i), rv(i)); end loop; end if; RETURN result; end "and"; end PACK1164; Changed from logic to ulogic EE514

  16. Subprogram overloading package SUBPROG is procedure MUX21( signal SEL : in bit; signal DIN0 : in bit; signal DIN1 : in bit; signal DOUT : out bit); procedure MUX21( signal SEL : in bit; signal DIN0 : in bit_vector; signal DIN1 : in bit_vector; signal DOUT : out bit_vector); end SUBPROG; package body SUBPROG is procedure MUX21( signal SEL : in bit; signal DIN0 : in bit; signal DIN1 : in bit; signal DOUT : out bit) is begin case SEL is when '0' => DOUT <= DIN0; when others => DOUT <= DIN1; end case; end MUX21; procedure MUX21( signal SEL : in bit; signal DIN0 : in bit_vector; signal DIN1 : in bit_vector; signal DOUT : out bit_vector) is begin case SEL is when '0' => DOUT <= DIN0; when others => DOUT <= DIN1; end case; end MUX21; end SUBPROG; EE514

  17. Subprogram return values & types architecture RTL of SUBRETN is begin C <= INV(A)(2 to 4); LA <= C(C'left); RA <= C(C'right); RB <= INV(B)(4); LB <= INV(B)(1); end RTL; architecture ORDER of SUBRETN is begin C <= INV(A)(3 downto 1); end ORDER; architecture BOUND of SUBRETN is begin LB <= INV(A)(0); end BOUND; library IEEE; use IEEE.std_logic_1164.all; entity SUBRETN is signal A : std_logic_vector(7 downto 4); signal B : std_logic_vector(0 to 3); signal C : std_logic_vector(2 downto 0); signal LB, RB, LA, RA : std_logic; function INV (DIN : std_logic_vector) return std_logic_vector is variable result : std_logic_vector(1 to DIN'length); begin result := not DIN; return result; end INV; end SUBRETN; Errors- since range does not match the type of return value EE514

  18. Active CAD VHDL code window EE514

  19. Simulation for RTL of SUBRETN EE514

  20. Simulation for RTL of SUBRETN architecture RTL of SUBRETN is begin C <= INV(A)(2 to 4); LA <= C(C'left); RA <= C(C'right); RB <= INV(B)(4); LB <= INV(B)(1); end RTL; EE514

  21. Type casting and type qualification Type UNSIGNED and operator “+” declared in package std_logic_arith as follows type UNSIGNED is array (NATURAL range <>)of STD_LOGIC; function “+” (L: UNSIGNED; R: USIGNED) return STD_LOGIC_VECTOR; type casting can convert types and requires a single quote after type mark EE514

  22. Type casting and type qualification library IEEE; use IEEE.std_logic_1164.all; use IEEE.std_logic_arith.all; entity CONVTYPE is port ( RSTn, CLK : in std_logic; CNTR4 : out std_logic_vector(3 downto 0)); end CONVTYPE; architecture RTL of CONVTYPE is signal CNTR4_FF : std_logic_vector(3 downto 0); begin CNTR4 <= CNTR4_FF; p0 : process (RSTn, CLK) begin if (RSTn = '0') then CNTR4_FF <= std_logic_vector'("0000"); elsif (CLK'event and CLK = '1') then CNTR4_FF <=unsigned’(CNTR4_FF) + unsigned'("0001"); end if; end process; end RTL; EE514

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