1. Hao wang and Jyh-Charn (Steve) Liu
FPGA Introduction
Hao wang and Jyh-Charn (Steve) Liu

2. What is an FPGA? Field Programmable Gate Array
Configurable Logic blocks (CLB), interconnection resources, and I/O pads.

3. How FPGA works?
CLB consists of two slices, each of which contains look-up tables (LUT), registers, multiplexers, and carry logic.
LUT implement logic functions
Registers store data
Multiplexers select the desired output
Carry logic enables fast arithmetic function
Interconnections are routing resources including channels, switch boxes, clock distribution networks, etc.

4. CLB architecture
Arrangement of slices within the CLB

5. Slice diagram

6. Slice diagram

7. How LUT works An 2-input LUT configured as follows implements AND gate
It can be easily reconfigured to implement OR, XOR, NAND, and NOR gates, which are the basics to build up more complex functions.
Modern FPGAs have 6-input LUTs which can be cascaded to implement complex digital circuits.
Input 1
Input 2
Output 1

8. Interconnection architecture
Switch box topology

9. Interconnection architecture
Interconnection patterns

10. Which takes more chip area, logic or interconnects?

11. How to Reconfigure FPGA
Logic block functions and interconnections are specified using Hardware Description Language (HDL).
The HDL code is synthesized, mapped, placed ,routed and download onto the chip by vendor-provided tools

12. How to Reconfigure FPGA
Each time a new configuration is downloaded, the FPGA behaves like a new chip implementing a new function.
The configuration is lost when powered off, because theyare stored in SRAM.
However, the configuration file can be stored in external storage such as flash card or PROM so that the chip can automatically load it when powered on

13. Why use FPGA? Compared to CPU, FPGA has the following benefits
Performance
Throughput
Reliability
Compared to ASIC, FPGA has the following benefits
Reconfigurability
Cost
Time to market

14. Benefit over CPU: Performance
FPGA code runs in real time in nanoseconds.
All the logic blocks inside FPGA can run concurrently in parallel, since they are real hardware circuits.
If fully utilized, FPGA can implement a high performance many-core system.

15. Benefit over CPU : Throughput
FPGA has many high speed I/O pins to interface with memory, Ethernet, etc. It has dedicated channels for peripherals, unlike CPU whose peripherals share a bus.
FPGA vendors provide many high speed communication IP cores.

16. Benefit over CPU : Reliability
Software programs are usually built upon several layers of abstractions (driver, OS, etc) to help schedule tasks and share resources. They are at risk of incompatibility, resource contention, deadline violation, etc.
FPGA circuitry is a hard implementation, which is deterministic and well predictable.

17. Benefit over ASIC : Reconfigurability
ASIC can only do a specific job. If you want an extra function after an ASIC has been manufactured, design another one! While for FPGA, that is nothing but adding a piece of code and re-compile it.
Certain bugs are caught after the ASIC has been manufactured and distributed to customers. A recall may put the company into bankrupt. While for FPGA, developers can fix the bug in the HDL code and distribute the update to customers.

18. Benefit over ASIC : Cost
ASIC development is usually non-recurring engineering. Product fabrication also costs a lot of money.
FPGA vendors produce large volume of chips so that end users do not need to eat the fabrication cost. Reconfigurability of FPGA makes it reusable for different projects.

19. Benefit over ASIC : Time to market
ASIC needs cost many man-years to design, test, validate, and fabricate.
FPGA development boards usually come with a rich set of peripherals and IP cores which makes it ideal for rapid prototyping.

20. Questions?

21. Reference
Introduction to FPGA Technology: Top 5 Benefits.
FPGA introduction, Ovind Harboe
The Design Warrior's Guide to FPGAs
Virtex-6 FPGA Configurable Logic Block User Guide