Digital Design with VHDL

1. Digital Design with VHDL Presented by: Amir Masoud Gharehbaghi Email: amgh@mehr.sharif.edu

2. Concurrent Statements • Concurrent Signal Assignment • Component Instantiation Statement • Generate Statement • Process Statement • Block Statement • Concurrent Procedure Call Statement • Concurrent Assert Statement

3. Sequential Statements • Signal Assignment Statement • Variable Assignment Statement • IF Statement • Case Statement • Loop Statement • Wait Statement • Procedure Call Statement

4. Sequential Statements (cont.) • Next Statement • Exit Statement • Return Statement • Assertion Statement • Report Statement • Null Statement

5. Subprogram Declaration subprogram_specification IS subprogram_declarative_part BEGIN sequential statements END [subprogram_type] [designator]; subprogram_specification ::= PROCEDURE designator [ ( parameter_list ) ] | FUNCTION designator [ ( parameter_list ) ] RETURN type_name designator ::= identifier | operator_symbol

6. Mealy FSM using Function PROCESS (present , x) FUNCTION nxt_gen(present : state; x: BIT) RETURN state IS VARIABLE nxt: state; BEGIN CASE present IS WHEN a => IF x = '0' THEN nxt := a; ELSE nxt := b; END IF; … END CASE; RETURN nxt; END nxt_gen; BEGIN nxt <= nxt_gen(present, x); IF present = c AND x = '1' THEN z <= '1'; ELSE z <= '0'; END IF; END PROCESS;

7. Mealy FSM using Procedure PROCESS (present , x) PROCEDURE nxt_gen(present: state; x: BIT; SIGNAL nxt: OUT state) IS BEGIN CASE present IS WHEN a => IF x = '0' THEN nxt <= a; ELSE nxt <= b; END IF; … END CASE; END nxt_gen; BEGIN nxt_gen(present, x, nxt); IF present = c AND x = '1' THEN z <= '1'; ELSE z <= '0'; END IF; END PROCESS;

8. Concurrent Procedure Call ARCHITECTURE test1 of test IS PROCEDURE apply(…) IS BEGIN … END; BEGIN apply(…); END;

9. Package Declaration PACKAGE identifier IS package_declarative_part END [PACKAGE] [package_name] PACKAGE BODY package_name IS package_body_declarative_item END [PACKAGE BODY] [package_name]

10. std_logic package PACKAGE std_logic_1164 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 "and" ( l, r : std_ulogic_vector ) RETURN std_ulogic_vector; END std_logic_1164;

11. std_logic Package Body PACKAGE BODY std_logic_1164 IS TYPE stdlogic_table IS ARRAY(std_ulogic, std_ulogic) OF std_ulogic; 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' ) -- | - | );

12. std_logic Package Body FUNCTION "and" ( l,r : std_ulogic_vector ) RETURN std_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 FOR i IN result'RANGE LOOP result(i) := and_table (lv(i), rv(i)); END LOOP; RETURN result; END "and"; END std_logic_1164;

13. Alias Declaration ALIAS identifier [ : type] IS name ; -> alias : an alternative name given to - an object - an indexed part of it - a slice of it

14. Record Type TYPE identifier IS RECORD element_declaration { element_declaration } END RECORD; element_declaration ::= identifier : type ;

15. Record Example TYPE instruction_format IS RECORD opc : opcode ; mode : mode_type ; adr : address_type ; END RECORD; … SIGNAL instr: instruction_format; … Instr.adr <= “10110000”;

16. ACCESS Type (pointers) TYPE node; TYPE pointer IS ACCESS node; TYPE node IS RECORD data: data_type; link: pointer; END RECORD;

17. ACCESS Type (cont.) VARIABLE head: pointer := NULL; … head := NEW node; … Head.link := NEW node;

18. Assert & Report Statement ASSERT condition REPORT “message” SEVERITY severity_level ; REPORT “message” SEVERITY severity_level ; severity_level ::= NOTE | WARNING | ERROR | FAILURE

19. Setup & Hold Time ASSERT NOT((clk = ‘1’ AND NOT clk’STABLE) AND data’STABLE(setup_time)) REPORT “Setup Time Violation” SEVERITY WARNING; ASSERT NOT(data’EVENT AND clk = ‘1’ AND NOT clk’STABLE(hold_time)) REPORT “Hold Time Violation” SEVERITY WARNING;