ECE 506 Reconfigurable Computing Lecture 2 Reconfigurable Architectures Ali Akoglu

Early Work °How is it possible that a hardware device, whose structure is normally fixed at fabrication time cannot be changed anymore during the lifetime, can be readapted at run-time to dynamically match the application requirements? °Historical perspective °FPGA technology

Early Work: Gerald Estrin- FixPlus Machine 1959 °Introduced the concept of reconfigurable computing. °The Fix-Plus Machine published in 1960, defines the concept of reconfigurable computing paradigm. °The economic feasibility of the system is based on utilization of essentially the same hardware in a variety of special purpose structures. This capability is achieved by programmed or physical restructuring of a part of the hardware.

Early Work A variable part (V) consists of various digital substructures that can be reorganized in problem-oriented special purpose configurations. problem-specific optimized functional units (trigonometric functions, logarithm, exponentials, n-th power, roots, complex arithmetic, hyperbolic, matrix operation). Speed gain over IBM7090 (2.5 to 1000) for accelerating Eigenvalues computation of matrices

Early Work The basic building blocks of Fix-Plus Machine ten diodes and four output drivers and is for combinatorial application four amplifiers and associated input logic for signal inversion, amplification, or high-speed storage

Early Work °The basic block modules inserted into any of 36 positions on a motherboard that provides the functionality for a given application. °The connection between the modules is established through a wiring harness °Function Reconfiguration means changing some modules °Routing Reconfiguration means changing parts of the wiring harness

Manual Reconfiguration

Programmable Logic Devices °Fact: A Boolean function can be written as a sum of products (AND/OR, NOR/NAND) °Result: Programmable Logic Array (PLA) and Programmable Array Logic (PAL) Unlike a logic gate, which has a fixed function, a PLD has an undefined function at the time of manufacture. Before the PLD can perform in a circuit it must be programmed. °The first programmable logic devices were produced by the Advanced Micro Devices (AMD) corporation. °The PLD business split from AMD under the name Vantis, and was acquired by Lattice Semiconductor in 1999.

Programmable Logic Array °Introduced in 1975, the most user-configurable of the traditional two-level programmable logic devices °In Boolean terms, this means a number of AND gates whose outputs feed into a large OR gate that drives one output. °By selecting which inputs drive each AND gate, and which AND gates drive the OR gate, any Boolean function can be created.

Unprogrammed device

Programmed device °Unwanted connections are "blown"

PLA vs PAL! °PAL: AND array is programmable, but OR array is fixed during fabrication. OR array has access to only subset of product terms.

Programmed PAL °4 product terms per each OR gate

Limitation of PALs and PLAs °Low capacity and speed size of the plane grows too quickly n times the number of inputs and outputs requires nxn as much chip area too costly logic gets slower as number of inputs to AND array increases °Available in small sizes, equivalent to a few hundred logic gates °Solution: Complex Programmable Logic Device multiple PLDs with a relatively small (fast) programmable interconnect less general than a single large PLD, but we can use software to partition our design into smaller PLD blocks

Complex Programmable Logic Device

°Hierarchical design against size explosion of PLAs Combinational logic with Flip Flops (registered output) Organized into logic blocks connected in an interconnect matrix Usually enough logic for simple counters, state machines, decoders, etc. °Non-volatile! Programming kept on power down Functions available instantly on system power up Hard to steal stored design CPLDs are used in many systems for configuration of the main reconfigurable device at start up.

Xilinx CoolRunner II CPLD °PLA and Macrocell combination °1.8V device, estimated power consumption of less than 100 micro amps °Up to 12,000 gates, 512 MacroCells

Complex Programmable Logic Device °Contains from macrocells °Each macrocell is equivalent to around 20 gates °Support up to 200 I/O pins °The key resource in a CPLD is the programmable interconnect Tradeoff between space for macrocells and space for interconnect

FPGA °Introduced in 1985 by Xilinx °Similar to CPLDs °A function to be implemented in FPGA Partitioned into modules, each implemented in a logic block. Logic blocks connected with the programmable interconnection.

FPGA Technology °1) Antifuse-based Realization of interconnections °2) Memory-based. realization of interconnections and computation SRAM, EEPROM and Flash