![The Role of Hardware Description Languages
cells
modules
chips
boards
algorithms
register transfers
Boolean expressions
transfer functions
processors
registers
gates
transistors
PHYSICAL
BEHAVIORAL STRUCTURAL
[Gajski and Kuhn]
• Design is structured around a hierarchy of representations
• HDLs can describe distinct aspects of a design at multiple
levels of abstraction](https://image.slidesharecdn.com/l1vhdlintro1-221001145339-74469d57/85/L1_vhdl_Intro-1-ppt-13-320.jpg)
![Entity Declaration
entity NAME_OF_ENTITY is
port (signal_names: mode type;
signal_names: mode type;
:
signal_names: mode type);
end [NAME_OF_ENTITY] ;
• NAME_OF_ENTITY: user defined
• signal_names: list of signals (both input and
output)
• mode: in, out, buffer, inout
• type: boolean, integer, character, std_logic](https://image.slidesharecdn.com/l1vhdlintro1-221001145339-74469d57/85/L1_vhdl_Intro-1-ppt-20-320.jpg)
L1_vhdl_Intro (1).ppt
- 1. Digital System Design Subject Name : Digital System Design Course Code : IT-314
- 2. Text-books 1. Digital System Design using VHDL by C.H. Roth. 2. Circuit Design with VHDL by Volnei A. Pedroni;
- 3. Reference Book 1. VHDL Primer by J. Bhasker; Addison Wesley Longman Pub. 2. Introduction to Digital Systems by M. Ercegovec, T. Lang and L.J. Moreno; Wiley 3. VHDL: Analysis & Modeling of Digital Systems by Z. Navabi; MGH 4. VHDL Programming by Examples by Douglas L. Perry; TMH 5. VHDL by Douglas Perry 6. The Designer Guide to VHDL by P.J. Ashendem; Morgan Kaufmann Pub. 7. Digital System Design with VHDL by Mark Zwolinski; Prentice Hall Pub. 8. Digital Design Principles and Practices by John F. Wakerly, Prentice Hall (third Edition) 2001 includes Xilinx student edition).
- 4. Overview What is digital system design? – Use of available digital components • Microprocessor, e.g. Pentium • Micro-controller, e.g. 8051 • Digital processing units, e.g. counters, shift registers. – Combine them to become a useful system
- 5. Programmable logic vs. microcontrollers in prototyping • In some situation you can design a digital system using programmable logic or microcontrollers • Programmable logic – more general and flexible, economic for mass production • Microcontrollers – more specific and less flexible, cost more in mass production
- 6. VHDL • What is VHDL? V H I S C Very High Speed Integrated Circuit Hardware Description Language IEEE Standard 1076-1993
- 7. History of VHDL • Designed by IBM, Texas Instruments, and Intermetrics as part of the DoD funded VHSIC program • Standardized by the IEEE in 1987: IEEE 1076-1987 • Enhanced version of the language defined in 1993: IEEE 1076-1993 • Additional standardized packages provide definitions of data types and expressions of timing data – IEEE 1164 (data types) – IEEE 1076.3 (numeric) – IEEE 1076.4 (timing)
- 8. Traditional vs. Hardware Description Languages • Procedural programming languages provide the how or recipes – for computation – for data manipulation – for execution on a specific hardware model • Hardware description languages describe a system – Systems can be described from many different points of view • Behavior: what does it do? • Structure: what is it composed of? • Functional properties: how do I interface to it? • Physical properties: how fast is it?
- 9. Usage • Descriptions can be at different levels of abstraction – Switch level: model switching behavior of transistors – Register transfer level: model combinational and sequential logic components – Instruction set architecture level: functional behavior of a microprocessor • Descriptions can used for – Simulation • Verification, performance evaluation – Synthesis • First step in hardware design
- 10. Why do we Describe Systems? • Design Specification – unambiguous definition of components and interfaces in a large design • Design Simulation – verify system/subsystem/chip performance prior to design implementation • Design Synthesis – automated generation of a hardware design
- 11. Digital System Design Flow Requirements Functional Design Register Transfer Level Design Logic Design Circuit Design Physical Design Description for Manufacture Behavioral Simulation RTL Simulation Validation Logic Simulation Verification Timing Simulation Circuit Analysis Design Rule Checking Fault Simulation • Design flows operate at multiple levels of abstraction • Need a uniform description to translate between levels • Increasing costs of design and fabrication necessitate greater reliance on automation via CAD tools – $5M - $100M to design new chips – Increasing time to market pressures
- 12. A Synthesis Design Flow Requirements Functional Design Register Transfer Level Design Synthesis Place and Route Timing Extraction VHDL Model ( VHDL) VHDL Model Logic Simulation Behavioral Simulation • Automation of design refinement steps • Feedback for accurate simulation • Example targets: ASICs, FPGAs
- 13. The Role of Hardware Description Languages cells modules chips boards algorithms register transfers Boolean expressions transfer functions processors registers gates transistors PHYSICAL BEHAVIORAL STRUCTURAL [Gajski and Kuhn] • Design is structured around a hierarchy of representations • HDLs can describe distinct aspects of a design at multiple levels of abstraction
- 14. Domains and Levels of Modeling high level of abstraction Functional Structural Geometric “Y-chart” due to Gajski & Kahn low level of abstraction
- 15. Domains and Levels of Modeling Functional Structural Geometric “Y-chart” due to Gajski & Kahn Algorithm (behavioral) Register-Transfer Language Boolean Equation Differential Equation
- 16. Domains and Levels of Modeling Functional Structural Geometric “Y-chart” due to Gajski & Kahn Processor-Memory Switch Register-Transfer Gate Transistor
- 17. Domains and Levels of Modeling Functional Structural Geometric “Y-chart” due to Gajski & Kahn Polygons Sticks Standard Cells Floor Plan
- 18. Basic VHDL Concepts • Interfaces • Modeling (Behavior, Dataflow, Structure) • Test Benches • Analysis, elaboration, simulation • Synthesis
- 19. Basic Structure of a VHDL File • Entity – Entity declaration: interface to outside world; defines input and output signals – Architecture: describes the entity, contains processes, components operating concurrently
- 20. Entity Declaration entity NAME_OF_ENTITY is port (signal_names: mode type; signal_names: mode type; : signal_names: mode type); end [NAME_OF_ENTITY] ; • NAME_OF_ENTITY: user defined • signal_names: list of signals (both input and output) • mode: in, out, buffer, inout • type: boolean, integer, character, std_logic
- 21. Architecture • Behavioral Model: architecture architecture_name of NAME_OF_ENTITY is -- Declarations ….. ….. begin -- Statements end architecture_name;
- 22. Half Adder library ieee; use ieee.std_logic_1164.all; entity half_adder is port( x,y: in std_logic; sum, carry: out std_logic); end half_adder; architecture myadd of half_adder is begin sum <= x xor y; carry <= x and y; end myadd;
- 23. Entity Examples … entity half_adder is port( x,y: in std_logic; sum, carry: out std_logic); end half_adder; FULLADDER A B C SUM CARRY
- 24. Architecture Examples: Behavioral Description • Entity FULLADDER is port ( A, B, C: in std_logic; SUM, CARRY: in std_logic); end FULLADDER; • Architecture CONCURRENT of FULLADDER is begin SUM <= A xor B xor C after 5 ns; CARRY <= (A and B) or (B and C) or (A and C) after 3 ns; end CONCURRENT;
- 25. Architecture Examples: Structural Description … • architecture STRUCTURAL of FULLADDER is signal S1, C1, C2 : bit; component HA port (I1, I2 : in bit; S, C : out bit); end component; component OR port (I1, I2 : in bit; X : out bit); end component; begin INST_HA1 : HA port map (I1 => B, I2 => C, S => S1, C => C1); INST_HA2 : HA port map (I1 => A, I2 => S1, S => SUM, C => C2); INST_OR : OR port map (I1 => C2, I2 => C1, X => CARRY); end STRUCTURAL; I1 S HA I2 C I1 S HA I2 C I1 OR I2 x A C B CARRY SUM S1 C1 C2
- 26. … Architecture Examples: Structural Description Entity HA is PORT (I1, I2 : in bit; S, C : out bit); end HA ; Architecture behavior of HA is begin S <= I1 xor I2; C <= I1 and I2; end behavior; Entity OR is PORT (I1, I2 : in bit; X : out bit); end OR ; Architecture behavior of OR is begin X <= I1 or I2; end behavior;
- 27. One Entity Many Descriptions • A system (an entity) can be specified with different architectures Entity Architecture A Architecture B Architecture C Architecture D
- 28. Test Benches • Testing a design by simulation • Use a test bench model – an architecture body that includes an instance of the design under test – applies sequences of test values to inputs – monitors values on output signals • either using simulator • or with a process that verifies correct operation