Benefits of Partial Reconfiguration
• Reducing the size of the FPGA device required to
implement a given function, with consequent
reductions in cost and power consumption
• Providing flexibility in the choices of algorithms
or protocols available to an application
• Enabling new techniques in design security
• Improving FPGA fault tolerance
• Accelerating configurable computing
Definitions
Partial Reconfiguration (PR)
Partial Reconfiguration is modifying a subset of logic in an
operating FPGA design by downloading a partial
configuration file.
Partition
Logical section of the design, defined by the user, to be
considered for design reuse. This is the section of the FPGA
designated for PR.
Definitions
Configuration Frame
The smallest addressable segments of the FPGA
configuration memory space. Reconfigurable frames are
built from discrete numbers of these lowest level elements
Frame
The smallest reconfigurable region within an FPGA device.
Frame in Virtex-6 are 40 CLBs high by 1 CLB wide.
Frame in Virtex-5 are 20 CLBs high by 1 CLB wide.
Frame in Virtex-4, are 16 CLBs high by 1 CLB wide.
Partition Pins
• Logical and physical connection between static
logic and reconfigurable logic.
• Formerly known as “Bus Macros”.
• Now they are automatically created for all
Reconfigurable Partition ports, no manual
reconfiguration is needed from the user.
Partition Pins – Proxy Logic
• Each partition pin is connected to a LUT,
These LUTs are called “Proxy Logic”
• Logically located in the Static Region
• Required to be at a fixed known point to act as
an interface between static and reconfigurable
partitions
Partition Pins
Bus Macro Implementation
PR Region Selection
Internal Configuration Access Port
(ICAP)
• Port to read and write the FPGA configuration
at run time
• enables a user to write software programs for
an embedded processor that modifies the
circuit structure and functionality during the
circuit’s operation.
• Allows for automated runtime reconfiguration
Hardware ICAP Core
Example Self Reconfiguration System
Two Ways to update LUTS
• Modular Partial Reconfiguration:
– Large changes
– Full module is changed between two
configurations
• Difference Partial Reconfiguration
– Small Changes
– Modify a LUT function or a memory content
Modular Layout
Constraints of Modular Method
• The size and the position of a module cannot be
changed.
• Input-output blocks (IOBs) are exclusively
accessible by contiguous modules.
• Reconfigurable modules can communicate only
with neighbor modules, and it must be done
through bus macros.
• No global signals are allowed (e.g., global reset),
with the exception of clocks that use a different
bitstream and routing channels.
Difference Based Partial
Reconfiguration
• Small changes on the FPGA configuration
• Manually done using the FPGA Editor
• What can be modified?
– LUTs equations
– BRAM contents and BRAM write modes
– I/O standards and pull-ups or pull-downs on external
pins
– muxes that invert polarity,
– Flipflop initialization and reset values,
• What cannot be modified?
– Routing – very dangerous: internal contentions.
Problems with Difference Based
Method
• Lack of Automation – Changes must be done
manually
• In complex designs it is difficult to find the
component you want to modify
• Xilinx current support is mostly for modular
based method.
The Early-Access Partial
Reconfiguration Design Flow
(The Old Way - used by the paper)
This design flow
is no longer
valid using
newer Xilinx
tools.
The New Way – A little easier
1. Synthesize base system with reconfigurable
module with input and output pins (XPS)
2. Create software files to manage PR Region
(SDK)
3. Use Plan Ahead to manage PR Region and
create bit-streams (Lots of steps here)
4. Merge bit-streams into download.bit to run
on the FPGA
Customizing Virtual Networks with
Partial FPGA
Reconfiguration
• Use reconfiguration to create/modify a virtual
network
• Heuristic to assign networks to HW/SW
• Allows for migration of virtual networks
between HW and SW
• Workstation handles SW while FPGA handles
HW
Motivation
• Network applications have diverse
performance requirements for underlying
network infrastructure
• Desire Flexibility, performance and isolation
• Numerous hardware network substrates
would work, but the hardware
implementation overhead is too high
• Need for straight-forward reconfigurationover-time method
Limitations of Current State of the Art
Current Implementation Pros
Cons
Software virtual
networks on
microprocessors
High Flexibility
and Isolation
Low performance
Network processors /
dedicated hardware
High
Performance
Hardware shuts
down during
reconfiguration
(Low isolation)
Low performance
when reconfiguring
(Low isolation)
Migrate networks to
software when
reconfiguring
Flexible
High
Performance
Flexible
Related Work
• Supercharging Planet Lab (SPL)
– Intel IXP Network Processors
– Dedicated ternary content addressable memory
(TCAM) for each forwarding table
• FPGA implementation
– 4 concurrent virtual networks with dedicated
– Dedicated IP routers
– Additional networks run in software
– Switch to software when reconfiguring
Related Work
• Field Programmable Port Extender (FPX)
– High speed switch
– PR packet processing modules using APIs
– Specialized software (PARBIT) for bit-stream
management and generation
– PR network processor
– Reconfigurable Accelerator for packet processing
functions
Proposed Approach
• Use reconfiguration to create/modify a virtual
network
• Heuristic to assign networks to HW/SW
• Allows for migration of virtual networks
between HW and SW
• Workstation handles SW while FPGA handles
HW
System Design
Partially Reconfigurable FPGA System
Static Region
PR Region
Arbiter
Header Verification
Packet Classifier
Checksum Verification
Output Queues
IP Lookup
CPU Transceiver
ARP Lookup
Time to live (TTL) Lookup
System Design
Software Based System
OpenVZ – lightweight virtualization apporach
FPGA receives packets and send them to HW or SW
CPU Transeiver sends the packet to the workstation
OpenVZ processes the packet on a virtual network
All processed packets go to the output queues on FPGA
System Design
Dynamic Virtual Network Allocation
• Virtual network removal
• Virtual network addition
• Virtual network bandwidth adjustment
– Reduction -> No effect on other networks
– Increase -> Greedy Rebalancing Algorithm:
Migrate lowest bandwidth to software or the
highest bandwidth to hardware to make room for
adjustment
System Implementation
Experimental Approach
•
•
•
•
Used EARP design flow to generate bitstreams
Used Bus-Macros
Separate Verilog files for all modules
Downloaded to the FPGA using JTAG
Experiment Testbed
Throughput of Routers
Static Reconfigurable Method
Why is there such a drop in performance in this method?
Partial Reconfigurable Method
Why is A unaffected by the reconfiguration like in previous method?
There isn’t much of a performance gain between the highest
performing PR and SR methods. Why?
What causes the SR method to outperform the PR method as the
number of Virtual Networks increases?
Hot-Spot Mitigation
• Use Partial Reconfiguration to swap hot and
cool modules around the chip based on a
thermal trigger.
• Set a threshold temperature and when a
module reaches that threshold, swap
positions with a cool module using
reconfiguration
Hot-Spot Mitigation
Module the size of ¼ a Microblaze
Module the size of ½ a Microblaze
Module the size of one Microblaze
Pixel Video Processor
• PR modules can be reconfigured to perform
arbitrary one pixel functions
• Tested to see how the reconfiguration time
overhead effects the system
Pixel Processor
My Project: Data Adaptable Reconfiguration