Vhdl 1 ppg


Published on

Published in: Education, Technology, Design
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Vhdl 1 ppg

  1. 1. By Prof P P GhadekarVishwakarma Institute of Technology, Pune
  2. 2. Presentation OutlineOverview of VHDLVHDL Fundamentals Libraries and Packages Entities, Architectures, and Configurations Signals Data Types Operators Essential Language Statements Advanced Language StatementsVHDL ExamplesSynthesis Vs. Simulation 2
  3. 3. Overview of VHDL V ery High Speed Integrated Circuit H ardware D escription L anguage VHDL language can be regarded as combination of followinglanguages Sequential Language+ Concurrent Language+ Netlist Language+ Timing Specifications+ Waveform genration Language+ VHDL is a language that can be used to describe the structure and / or behaviour of hardware designs VHDL designs can be simulated and / or synthesized VHDL Hierarchical use of VHDL designs permits the rapid creation of complex hardware designs 3
  4. 4. History of VHDLVHDL was developed by the VHSIC (Very High Speed IntegratedCircuit) Program in the late 1970s and early 1980sVHDL was designed to be a documentation and simulation languageVHDL is now used widely by industry and academia for bothsimulation and synthesisTwo versions of VHDL have been standardized by the IEEE: • VHDL87 - IEEE-1076-1987 • VHDL93 - IEEE-1076-1993 4
  5. 5. Features of VHDLVHDL has powerful constructsIn VHDL, design may be decomposed hierarchicallyEach design elements has a well defined interface useful for connectingit to other elements.Test bench is available for SimulationVHDL handles asynchronous & synchronous sequential circuits.In VHDL, concurrency, timing and clocking can be modeled.In VHDL, design is target independent.VHDL support design library.The language is not case sensitive.A Formal Language for Specifying the Behavior and Structure of aDigital CircuitAllows Top-Down Design 5
  6. 6. Libraries and PackagesLibraries provide a set of hardware designs, components, and functionsthat simplify the task of designingPackages provide a collection of commonly used data types andsubprograms used in a designThe following is an example of the use of the IEEE library and itsSTD_LOGIC_1164 package: LIBRARY ieee; USE ieee.std_logic_1164.ALL; 6
  7. 7. Entities, Architectures, and Configurations• The structure of a VHDL design resembles the structure of a modern, object-oriented software design in the sense that every VHDL design describes both an external interface and an internal implementation• A VHDL design consists of entities, architectures, and configurations 7
  8. 8. EntitiesAn Entity is something that has separate real existence.An entity is a specification of the design’s external interface.Entity declarations specify the following: • Name of the entity • Set of port declarations defining the inputs and outputs to the hardware designThe following is an example of an entity declaration: ENTITY andgate IS PORT ( a : IN STD_LOGIC; b : IN STD_LOGIC; c : OUT STD_LOGIC ); END andgate; 8
  9. 9. ArchitecturesAn architecture is a specification of the design’s internalimplementationMultiple architectures can be created for a particular entityThe following is an example of an architecture declaration: ARCHITECTURE r001 OF andgate IS BEGIN c <= a AND b; END r001; 9
  10. 10. Entity-Architecture Pairentity name port names port mode (direction) port type punctuation reserved words 10
  11. 11. VHDL Program Structure 11
  12. 12. PortsPort name choices: Consist of letters, digits, and/or underscores Always begin with a letter Case insensitivePort direction choices: IN Input port OUT Output port INOUT Bidirectional port BUFFER Buffered output portPort signal type (suggested) choices: STD_LOGIC STD_LOGIC_VECTOR(<max> DOWNTO <min>) 12
  13. 13. ConfigurationsA configuration is a specification of the mapping between anarchitecture and a particular instance of an entityA configuration exists for each entityThe default configuration maps the most recently compiled architectureto the entityConfigurations are often used to specify alternative simulation modelsfor hardware designs 13
  14. 14. SignalsSignals represent wires and storage elements within a VHDL designSignals may only be defined inside architecturesSignals are associated with a data typeSignals have attributesIt holds a list of values, which includes current value of the signal, anda set of possible future values that are to be appears on the signal.Future values can be assigned to a signal using a signal assignmentstatement i.e. <= 14
  15. 15. Process Statement Process is a main concurrent statement in VHDL code. It describe the sequential behavior of the design. All statement within process executes sequentially in zero time. Only one driver is placed on a signal. The signal is updated with the last value assigned to it with in the process. Syntax→ begin process(sensitivity list) begin ------ ------ end process Sensitivity List- List of signal on which process should execute afterarranging its state. Every process must have either sensitivity list or waitstatement. 15
  16. 16. Process Statements-- Assume that the following ports exist for this entitySIGNAL a, b, sel :IN STD_LOGIC;SIGNAL x, y :OUT STD_LOGIC;PROCESS (a, b, sel)-- a, b, and sel are in the sensitivity list to indicate-- that they are inputs to the processBEGINIF (a = ’0’) THEN -- Only valid in a process x <= a OR b;ELSIF (b = ’0’) THEN x <= a XNOR b;ELSE x <= ’0’;END IF;CASE sel IS -- Only valid in a process WHEN ‘0’ => y <= a AND b; WHEN OTHERS => y <= ‘1’;END CASE;END PROCESS; 16
  17. 17. Built-In Data TypesVHDL supports a rich set of built-in data types as well as user-defined data types.Built-in data types work well for simulation but not so well forsynthesis Data Type Characteristics BIT Binary, Unresolved BIT_VECTOR Binary, Unresolved, Array INTEGER Binary, Unresolved, Array REAL Floating Point Examples: A: in bit; G: out boolean; D: in bit_vector(0 to 7); E: in bit_vector(7 downto 0); 17
  18. 18. STD_LOGIC_1164 Data Types STD_LOGIC_1164 is a standardized package that implements a set of data types Data Type Characteristics STD_ULOGIC MVL – 9, Unresolved STD_ULOGIC_VECTOR MVL – 9, Unresolved, Array STD_LOGIC MVL – 9, Resolved STD_LOGIC_VECTOR MVL – 9, Resolved, ArrayIEEE recommends the use of the STD_LOGIC and STD_LOGIC_VECTOR data types 18
  19. 19. Logical OperatorsVHDL supports the following logical operators: AND OR XOR XNOR NOT NAND NORVHDL also supports the overloading of existing operators and thecreation of new ones 19
  20. 20. Assignment StatementsSIGNAL x, y, z : STD_LOGIC;SIGNAL a, b, c : STD_LOGIC_VECTOR(7 DOWNTO 0);SIGNAL sel : STD_LOGIC_VECTOR(2 DOWNTO 0);-- Concurrent Signal Assignment Statements-- NOTE: Both x and a are produced concurrentlyx <= y AND z;a <= b OR c;-- Alternatively, signals may be assigned constantsx <= ’0’;y <= ’1’;z <= ’Z’;a <= "00111010"; -- Assigns 0x3A to ab <= X"3A"; -- Assigns 0x3A to bc <= X"3" & X"A"; -- Assigns 0x3A to c 20
  21. 21. Assignment Statements (cont.)SIGNAL x, y, z :STD_LOGIC;SIGNAL a, b, c :STD_LOGIC_VECTOR( 7 DOWNTO 0);SIGNAL sel :STD_LOGIC_VECTOR( 2 DOWNTO 0);-- Conditional Assignment Statement-- NOTE: This implements a tree structure of logic gatesx <= ’0’ WHEN sel = “000” ELSE y WHEN sel = “011” ELSE z WHEN x = ’1’ ELSE ’1’;-- Selected Signal Assignment Statement-- NOTE: The selection values must be constantsWITH sel SELECTx <= ’0’ WHEN “000”, y WHEN “011”, z WHEN “100”, ’1’ WHEN OTHERS;-- Selected signal assignments also work with vectorsWITH x SELECTa <= “01010101” WHEN ’1’, b WHEN OTHERS; 21
  22. 22. AND-NAND Example 22
  23. 23. Different Modeling StylesThe architectural body between begin and end can have only one of thefollowing modeling stylesBehavioral ModelingData flow ModelingStructural Modeling 23
  24. 24. Behavioral Style of Modeling• The behavioral style of modeling specifies the behavior of an entity as a set of statement that are executed sequentially in the specified order.• A ‘Process’ statement is a key element in the behavioral modeling. A process statement contains a set of sequential statements which specify the functionality of the model and not the exact structure of it.• Process Statement is a concurrent statement which executes in parallel With other concurrent statement s and other processes. 24
  25. 25. Data flow style of Modeling• In this type of modeling , the flow of the data is expressed primarily using concurrent signal assignment statements. The structure of the entity is not explicitly specified in this type of modeling but it is inferred from the equation.• The primary difference between Behavioral and Data flow modeling is that Behavioral modeling uses processes and other does not.• Data flow description are used in the cases where we have simple design equations of the circuit. 25
  26. 26. Structural style of Modeling• An architecture that uses components is often called as Structural modeling.• It defines the precise interconnection structure of signals and entities within that entity.• A pure Structural description is equivalent to a schematic diagram or net list of the circuit. 26
  27. 27. Complete Example• Example 1 -- A Package with a procedure modeling the functionality of an OR gatepackage gate is procedure Or_gate(signal In1, In2 : bit; signal Out1 : out bit);end gate;package body gate is procedure Or_gate(signal In1, In2 : bit; signal Out1 : out bit) is begin Out1 <= In1 or In2; end Or_gate;end gate; 27
  28. 28. Half Adder• Example 2 -- Behavioral Description of a Half Adderentity Half_adder is generic ( AB_to_sum : TIME := 0 ns; AB_to_carry : TIME := 0 ns ); port ( A : in bit; B : in bit; Sum : out bit; Carry : out bit );end Half_adder; 28
  29. 29. Half Adder (contd.)architecture Behavioral of Half_adder isbegin process begin Sum <= A xor B after AB_to_sum; Carry <= A and B after AB_to_carry; wait on A,B; end process;end Behavioral; 29
  30. 30. Full Adder• Example 2 -- Structural Description of a Full Adder that instantiates Half Adder and Uses procedure Or_gate from the package gate.use WORK.gate.all; -- use the Package gateentity Full_adder is port ( A : in bit; B : in bit; Carry_in : in bit; Sum : out bit; Carry_out : out bit );end Full_adder; 30
  31. 31. Full Adder (contd.)architecture structural of Full_adder iscomponent Half_adder generic ( AB_to_sum : TIME := 0 ns; AB_to_carry : TIME := 0 ns ); port ( A : in bit; B : in bit; Sum : out bit; Carry : out bit );end component;for all : Half_adder use entity work.Half_adder(behavioral); 31
  32. 32. Full Adder (contd.)signal Temp_sum : bit;signal Temp_carry1 : bit;signal Temp_carry2 : bit;begin U0 : Half_adder generic map (5 ns, 5 ns) port map (A, B, Temp_sum, Temp_carry1); U1 : Half_adder generic map (5 ns, 5 ns) port map (A => Temp_sum, B => Carry_in, Sum => Sum, Carry => Temp_carry2); U3 : Or_gate ( Temp_carry1, Temp_carry2, Carry_out);end structural; 32
  33. 33. Test Benchlibrary STD;use STD.standard.all;use STD.textio.all;library testpackage;use testpackage.testpackage.all;entity fa_test is -- Entity for the test benchend fa_test;architecture bench of fa_test iscomponent Full_adder -- Component declaration for Full Adder port ( A : in bit; B : in bit; Carry_in : in bit; Sum : out bit; Carry_out : out bit );end component; for all : Half_adder use entity work.Full_adder(Structural 33
  34. 34. Test Bench (contd.)signal A, B, Carry_in : bit;signal Sum, Carry_out : bit;signal temp : bit_vector(0 to 31);begina1: Full_adder port map ( A, B, Carry_in, Sum, Carry_out); A <= temp(31); B <= temp(30); Carry_in <= temp(29);a2: process variable sttr : line; variable rando : integer; file dataout : text is out "data.out";begin rando := 1; 34
  35. 35. Test Bench (contd.)for i in 0 to 40 loop temp <= int2vec(rando); rando := (rando * 3)/2 +1; wait for 1 ms; write(sttr, string((" A = ")); write(sttr, A); write(sttr, string((" B = ")); write(sttr, B); write(sttr, string((" Carry_in = ")); write(sttr, Carry_in); write(sttr, string((" Sum = ")); write(sttr, Sum); write(sttr, string((" Carry_out = ")); write(sttr, Carry_out); writeline (dataout, sttr); wait for 0 ns; end loop; wait;end process;end bench; 35
  36. 36. Basic VHDL Concepts• Interfaces• Behavior• Structure• Test Benches• Analysis, elaboration, simulation• Synthesis 36
  37. 37. Modeling Interfaces• Entity declaration – describes the input/output ports of a module entity name port names port mode (direction) entity reg4 is port ( d0, d1, d2, d3, en, clk : in bit; q0, q1, q2, q3 : out bit ); punctuation end entity reg4; reserved words port type 37
  38. 38. VHDL-87• Omit entity at end of entity declaration entity reg4 is port ( d0, d1, d2, d3, en, clk : in bit; q0, q1, q2, q3 : out bit ); end reg4; 38
  39. 39. Modeling Behavior• Architecture body – describes an implementation of an entity – may be several per entity• Behavioral architecture – describes the algorithm performed by the module – contains • process statements, each containing • sequential statements, including • signal assignment statements and • wait statements 39
  40. 40. Behavior Examplearchitecture behav of reg4 isbegin storage : process is variable stored_d0, stored_d1, stored_d2, stored_d3 : bit; begin if en = 1 and clk = 1 then stored_d0 := d0; stored_d1 := d1; stored_d2 := d2; stored_d3 := d3; end if; q0 <= stored_d0 after 5 ns; q1 <= stored_d1 after 5 ns; q2 <= stored_d2 after 5 ns; q3 <= stored_d3 after 5 ns; wait on d0, d1, d2, d3, en, clk; end process storage;end architecture behav; 40
  41. 41. VHDL-87• Omit architecture at end of architecture body• Omit is in process statement header architecture behav of reg4 is begin storage : process ... begin ... end process storage; end behav; 41
  42. 42. Modeling Structure• Structural architecture – implements the module as a composition of subsystems – contains • signal declarations, for internal interconnections – the entity ports are also treated as signals • component instances – instances of previously declared entity/architecture pairs • port maps in component instances – connect signals to component ports • wait statements 42
  43. 43. Structure Example bit0 d_latchd0 q0 d q clk bit1 d_latchd1 q1 d q clk bit2 d_latchd2 q2 d q clk bit3 d_latchd3 q3 d q gate clk and2en int_clk a yclk b 43
  44. 44. Structure Example • First declare D-latch and and-gate entities and architecturesentity d_latch is entity and2 is port ( d, clk : in bit; q : out bit ); port ( a, b : in bit; y : out bit );end entity d_latch; end entity and2;architecture basic of d_latch is architecture basic of and2 isbegin begin latch_behavior : process is and2_behavior : process is begin begin if clk = ‘1’ then y <= a and b after 2 ns; q <= d after 2 ns; wait on a, b; end if; end process and2_behavior; wait on clk, d; end architecture basic; end process latch_behavior;end architecture basic; 44
  45. 45. Structure Example• Now use them to implement a register architecture struct of reg4 is signal int_clk : bit; begin bit0 : entity work.d_latch(basic) port map ( d0, int_clk, q0 ); bit1 : entity work.d_latch(basic) port map ( d1, int_clk, q1 ); bit2 : entity work.d_latch(basic) port map ( d2, int_clk, q2 ); bit3 : entity work.d_latch(basic) port map ( d3, int_clk, q3 ); gate : entity work.and2(basic) port map ( en, clk, int_clk ); end architecture struct; 45
  46. 46. VHDL-87• Can’t directly instantiate entity/architecture pair• Instead – include component declarations in structural architecture body • templates for entity declarations – instantiate components – write a configuration declaration • binds entity/architecture pair to each instantiated component 46
  47. 47. Structure Example in VHDL-87 • First declare D-latch and and-gate entities and architecturesentity d_latch is entity and2 is port ( d, clk : in bit; q : out bit ); port ( a, b : in bit; y : out bit );end d_latch; end and2;architecture basic of d_latch is architecture basic of and2 isbegin begin latch_behavior : process and2_behavior : process begin begin if clk = ‘1’ then y <= a and b after 2 ns; q <= d after 2 ns; wait on a, b; end if; end process and2_behavior; wait on clk, d; end basic; end process latch_behavior;end basic; 47
  48. 48. Structure Example in VHDL-87• Declare corresponding components in register architecture body architecture struct of reg4 is component d_latch port ( d, clk : in bit; q : out bit ); end component; component and2 port ( a, b : in bit; y : out bit ); end component; signal int_clk : bit; ... 48
  49. 49. Structure Example in VHDL-87• Now use them to implement the register ... begin bit0 : d_latch port map ( d0, int_clk, q0 ); bit1 : d_latch port map ( d1, int_clk, q1 ); bit2 : d_latch port map ( d2, int_clk, q2 ); bit3 : d_latch port map ( d3, int_clk, q3 ); gate : and2 port map ( en, clk, int_clk ); end struct; 49
  50. 50. Structure Example in VHDL-87• Configure the register model configuration basic_level of reg4 is for struct for all : d_latch use entity work.d_latch(basic); end for; for all : and2 use entity work.and2(basic) end for; end for; end basic_level; 50
  51. 51. Mixed Behavior and Structure• An architecture can contain both behavioral and structural parts – process statements and component instances • collectively called concurrent statements – processes can read and assign to signals• Example: register-transfer-level model – data path described structurally – control section described behaviorally 51
  52. 52. Mixed Examplemultiplier multiplicandshift_regcontrol_ shift_section adder reg product 52
  53. 53. Mixed Exampleentity multiplier is port ( clk, reset : in bit; multiplicand, multiplier : in integer; product : out integer );end entity multiplier;architecture mixed of mulitplier is signal partial_product, full_product : integer; signal arith_control, result_en, mult_bit, mult_load : bit;begin arith_unit : entity work.shift_adder(behavior) port map ( addend => multiplicand, augend => full_product, sum => partial_product, add_control => arith_control ); result : entity work.reg(behavior) port map ( d => partial_product, q => full_product, en => result_en, reset => reset ); ... 53
  54. 54. Mixed Example … multiplier_sr : entity work.shift_reg(behavior) port map ( d => multiplier, q => mult_bit, load => mult_load, clk => clk ); product <= full_product; control_section : process is -- variable declarations for control_section -- … begin -- sequential statements to assign values to control signals -- … wait on clk, reset; end process control_section;end architecture mixed; 54