Welcome to the National Instruments presentation of the Spartan-3E Starter Board as an academic learning platform.

Transcription

1 Welcome to the National Instruments presentation of the Spartan-3E Starter Board as an academic learning platform. Understanding digital logic and FPGA concepts can be daunting for some undergraduate students, especially those not studying electrical engineering. To facilitate a long-term and engaging learning environment, there is a need for an intermediary hardware and software package that is cost-effective, easy to understand and to implement, and is adaptable with existing VHDL code.

2 Digital Design Fundamentals The NAND gate is the fundamental building block for digital logic. It is a combination of an AND gate coupled with a NOT gate at its output. The truth table above describes the output behavior of implementing a NAND gate on two bitwise inputs.

3 Digital Design Fundamentals NAND gates can be used in combination to implement logic that would traditionally be implemented with AND, OR, and NOT gates. Using NAND gates for combination logic is cost effective due to its logical completeness and inherent compactness. The figure to the top left shows a basic combination logic. The figure to the bottom left shows the same logic implemented using only NAND gates. Finally, the figure to the top right shows an equivalent combination logic after logic optimizations are performed.

4 Single Bit Adders: Half Adder To create even more complex combinational logic, truth tables can be used to describe implementation. For example, a half adder is a logic circuit that can perform an addition on two binary digits. The half adder produces a sum and a carry value which are both binary digits. Although logically concise, the half-adder cannot carry bits in multi-bit addition operations which is considered a drawback. [1] Wikipedia,

5 Single Bit Adders: Full Adder A full adder, solving many of the short comings of the half adder, is a logical circuit that performs an addition operation on three binary digits. The full adder produces a sum and carry value, which are both binary digits. It can work on its own or be combined with other full adders. As shown, the truth table simplifies logic understanding. [2] Wikipedia,

6 Using FPGAs to Replace Discrete Logic FPGA is short for Field Programmable Gate Array. The FPGA is a semiconductor with unconnected logic gates at the time of manufacture. Users can define and re-define functionality via software and this code is later downloaded to the chip for deployment. The FPGA offers flexible deployment options to the user since debugging at the hardware level can still be performed after code is downloaded. [3]

7 FPGA Hardware Basics An FPGA contains programmable logic components called "logic blocks", and programmable interconnects. Logic blocks can be programmed to perform the function of basic logic gates such as AND, and XOR, or more complex combinational functions such as decoders or simple mathematical functions. The architecture of the FPGAs vary from manufacturer to manufacturer, and often are differentiated by the number of logic cells that are available.

8 The typical basic FPGA architecture consists of an array of configurable logic blocks. An application circuit must be mapped into an FPGA with adequate resources. A classic FPGA logic block consists of a 4-input lookup table (LUT), and a flip-flop. Many FPGA vendors use LUTs to define the number of logic gates a FPGA can represent.

9 VHDL Software Basics VHDL is short for Very High Speed Integrated Circuit Hardware Description Language. VHDL is generally used to program FPGAs and ASICs. Over the years, it has become the industry standard for these hardware platforms. The main benefit of VHDL has been its ability to model and simulate hardware behavior prior to its synthesis into real hardware gates and interconnects. [4]

10 VHDL Framework & Syntax VHDL description of hardware is split into two sections, entities and hardware. Entities define the inputs and outputs of the hardware logic. Function declarations in C and C++ are similar in behavior. Architecture describes the hardware logic behind the entity. Essentially, this is the hardware implementation of the circuit. Function descriptions in C and C++ are similar in behavior.

11 VHDL Software Example: 1-Bit Adder The example snippet here is the VHDL implementation of the half-adder mentioned earlier. The entity section of the code defines inputs A and B and the outputs S and C. The architecture section describes the behavior of the inputs and outputs in relation to each other. In this code, A XOR (exclusive or) B value is assigned to the output S and A AND B value is assigned to the output C. With this architecture, a simple 1-bit adder is implemented with a small amount of code.

12 FPGA Implementation The figure shows the simplified diagrammatic flow of data in the FPGA. The inputs A and B are defined in the left I/O cells, the digital gates are implemented on the hardware level, and the data is carried to the outputs S and C through the interconnects.

13 LabVIEW FPGA Module The LabVIEW FPGA module is the National Instruments software for developing FPGA Logic and Real-Time Hardware. With LabVIEW FPGA, several different hardware platforms can be configured and programmed including: Spartan-3E Starter Board Plug-In Reconfigurable I/O (RIO) Boards by National Instruments CompactRIO Modular Reconfigurable I/O System by National Instruments Compact Vision System by National Instruments The LabVIEW FPGA Module provides an easy-to-use solution to programming a multitude of platforms. In a project based learning environment, the ease of LabVIEW FPGA module will allow students to understand the essentials of FPGA programming quickly and interactively.

14 LabVIEW FPGA Tool Chain LabVIEW FPGA integrates intuitive graphical programming techniques into the FPGA realm through a two-step translation process. The user develops VIs in a LabVIEW graphical programming environment. During program compilation, the LabVIEW FPGA module translates the LabVIEW code into VHDL code. The VHDL code is subsequently converted to a bitstream representation by the Xilinx onboard compiler and downloaded onto the FPGA target. Throughout this entire process, LabVIEW FPGA allows for a real-time debugging interaction with the user.

15 LabVIEW- A Natural Entity Architecture Pairing LabVIEW provides a natural transition to and from VHDL code. The front panel and connector pane of LabVIEW provides the same functionality as the entity of VHDL code. Within the front panel, users can define inputs and outputs, and the connector pane defines the datatypes of these parameters. Similarly, the block diagram provides the same functionality as the architecture of VHDL code. Within the block diagram, users describe the implementation of the code.

16 Building Higher Level Logic The LabVIEW FPGA module makes modular programming very easy to develop and implement. For example, the user can develop JK Flip Flops using NAND gates in the block diagram. A single JK Flip Flop can be built into a LabVIEW sub-function, called a SubVI, with a few clicks of the mouse then combined and interchanged with other SubVIs to develop more complex integrated logic circuits such as the 74LSxxx. Users new to modular programming will find LabVIEW s implementation to be intuitive and quick. Rather than spending much time learning modular programming techniques, users will be able to concentrate on fundamental FPGA concepts.

17 LabVIEW FPGA- More than Logic Generation LabVIEW s graphical interface offers much more than mere logic generation. Users can follow data flow during debugging, they can probe and see the data change as it moves through segments of code, and they can stop and pause program execution. In addition, the digital logic they would regularly need are in the user palettes for immediate implementation. The front panel provides graphical aids to immediately notify the user of hardware behavior with tools such as LEDs, switches, knobs, gauges, and much more. Whereas hardware behavior would be difficult to predict in VHDL code until actual compilation on the hardware, with LabVIEW FPGA, users can save time by emulating their code in LabVIEW prior to downloading.

18 LabVIEW FPGA G Programming Language LabVIEW FPGA is a G or Graphical Programming Language, therefore LabVIEW is inherently capable of parallel code execution. With the LabVIEW FPGA option, single cycle loops can be used to guarantee that the included code will run within a single cycle of the FPGA clock. LabVIEW FPGA allows users to program not only simple FPGA boards, but also high performance hardware from NI. LabVIEW FPGA assists greatly in projects that require hardware level execution, seamless integration, and fast time-to-application.

19 Benefits Using the parallel nature of graphical programming and the truly parallel implementation on the FPGA, users can separate code into different code segments which can run in parallel and achieve faster application execution. As users develop code, they can start thinking about logical pieces to break the code into different segments for faster execution. LabVIEW FPGA also provides a natural introduction to VHDL programming with the entity/architecture pairing. FPGA hardware is extremely reliable and customizable, allowing users to quickly change the behavior of their hardware via software. The flexibility of FPGA hardware combined with the ease of LabVIEW FPGA, allows users to quickly learn and develop FPGA applications.