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FPGA chips and DSP Algorithms

FPGA chips and DSP Algorithms. By Emily Fabes. Agenda. FPGA Background Reasons to use FPGA’s Advantages and disadvantages of using FPGA’s Sample VHDL code Questions. FPGA Background Information. F ield P rogrammable G ate A rrays

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FPGA chips and DSP Algorithms

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  1. FPGA chips and DSP Algorithms By Emily Fabes

  2. Agenda • FPGA Background • Reasons to use FPGA’s • Advantages and disadvantages of using FPGA’s • Sample VHDL code • Questions

  3. FPGA Background Information • Field Programmable Gate Arrays • Made up of Logic Blocks, I/O Blocks and Programmable Interconnect

  4. Programming FPGA’s • Method #1 – Using a hardware description language (e.g.. VHDL) • High level design for FPGA’s • Routing and wiring done automatically • Method #2 – Using placing components manually using a schematic drawing tool • Low level design for FPGA’s

  5. Circuit Implementation • Combinational Logic • No dependence on previous input values • Ex. AND gate, OR gate, NOT gate • Sequential Logic • Has dependence on previous input values • Contains a flip-flop, which give “memory” to the circuit

  6. Why Use FPGA’s? • High performance circuits previously implemented on ASIC’s • ASIC – Application Specific Integrated Circuit • ASIC’s have long design process • FPGA’s only recently became large enough to implement these applications • FPGA’s have become cheaper

  7. Why Use FPGA’s? • Better design tools have been made for circuit creation • Can upgrade the design later by reprogramming or upgrading the chip • New FPGA’s now offer hardwired multipliers throughout the chip • Makes multiply and accumulate easier and faster

  8. Advantage – Flexibility • Can designate more hardware to make a section faster • Can the chip use in different applications • Code blocks are reusable after they have been optimized

  9. Advantage – Precision • Precision can easily be added to any point in a circuit • Example VHDL code • signal u_k : std_logic_vector(15 downto 0); • signal u_k_3 : std_logic_vector(17 downto 0); • Disadvantage – takes up resources

  10. Advantage – Shifting • Shifting by multiples of two is easy and efficient • Virtually no hardware cost, just wiring • Can implement multiplies as combinations of shifts and adds • 3 = 20 + 21

  11. Disadvantage – Designers • Cannot just switch a DSP designer from a SHARC to a FPGA • Different style of thinking required • VHDL code is not like C even though it might look like C • VHDL creates circuits • Cannot just step through the code, parallel circuits running

  12. Disadvantage – Timing • Make sure that when using sequential circuits that data is valid when you need it • Routing delays

  13. Disadvantage – Optimization • Optimization is very hard • Must really understand what is going on and how this affects the timing of the circuit • Not so much code optimization as hardware optimization

  14. VHDL Code Example

  15. Covered • FPGA Background • Reasons to use FPGA’s • Advantages and disadvantages of using FPGA’s • Sample VHDL code

  16. References • http://www.optimagic.com/faq.html#FPGA • FPGA/DSP blend tackles telecom appsJennifer Eyre, Senior DSP Analyst, Berkeley Design Technology Inc., Berkeley, Calif. • Reduce Build Costs by Offloading DSP Functions to an FPGA http://www.fpgajournal.com/articles/behere.htm • Digital Design Principles and Practices by J Wakerly • ENEL 527 Lab 3

  17. Questions?

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