FPGA Latch Shift Register Layout to Reduce Wire Congestion
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Solution Overview
Problem
Field Programmable Gate Arrays (FPGAs) face inefficiencies in silicon utilization and cost due to the implementation of shift registers, which require extensive global interconnects and waste LUT logic resources, leading to wire congestion and suboptimal logic placement.
Innovation Solution
A shift register design that incorporates a latch within a basic logic element with a programmable interconnect, allowing for cross-coupling of LUT logic elements to minimize external interconnect usage and enable flexible placement of latches and shift registers within the FPGA fabric, thereby reducing wire congestion and enhancing silicon utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shift registers are implemented using prior-art FPGA logic elements with global interconnects, then shift register functionality is achieved, but wire congestion and silicon utilization efficiency deteriorate
Solution Approach 1:
The patent segments the shift register implementation into distributed latches placed throughout the FPGA fabric, with each latch using only local interconnect resources. This divides the monolithic global interconnect requirement into smaller local segments, eliminating wire congestion while maintaining shift register functionality.
Solution Approach 2:
The patent transitions from using global interconnect (two-dimensional routing across the entire FPGA) to local interconnect (one-dimensional routing within immediate neighborhood). This dimensional change in interconnect scope reduces complexity and wire congestion while preserving functionality.
2Reliability
If LUT logic resources are used to implement shift register stages, then shift register functionality is achieved, but silicon utilization efficiency deteriorates due to wasted LUTs
Solution Approach 1:
The patent makes LUT logic elements multi-functional by configuring them to operate as latches when used for shift register stages. This allows the same LUT resource to serve dual purposes: implementing logic functions when needed and serving as storage elements for shift registers, thereby eliminating wasted LUTs and improving silicon utilization efficiency.
Solution Approach 2:
The patent enables LUT logic elements to self-configure as latches through programmable control, eliminating the need for dedicated latch hardware. The LUTs serve themselves by reconfiguring their internal logic to provide storage functionality, maximizing resource utilization without requiring additional specialized components.
3Productivity
If dedicated shift registers are pre-positioned in the FPGA fabric, then silicon utilization improves, but adaptability to user requirements deteriorates
Solution Approach 1:
The patent introduces dynamics by making the shift register implementation reconfigurable through programmable logic. Instead of static pre-positioned dedicated shift registers, the system dynamically adapts to user requirements by configuring LUTs as latches wherever needed in the fabric, providing both high silicon utilization and full adaptability to user specifications.
Solution Approach 2:
The patent changes the operational parameters of LUT logic elements from pure logic computation to latch mode through programmable control. This parameter change enables the same hardware resources to adapt to different user requirements while maintaining high silicon utilization efficiency, resolving the contradiction between dedicated hardware efficiency and user flexibility.
Data Source
AI summary
Disclosed is a programmable logic device adapted to implement a shift register, the device comprising: a logic block comprised of: a latch having an input; and a logic element having an output capable of coupling to an adjacent logic block and the latch input, wherein the output is coupled to the adjacent logic block and decoupled from the latch input; and an interconnect coupled to the latch and adapted to transmit the latch output to an input of the logic element. In the device, the logic element is configured as a route through for the latch output to couple to the adjacent logic block.