FPGA language ( HDL ). Overview 3 4 Component-Based Software - PDF document

11/05/2016 Agenda  The topics that will be addressed are:  Overview on basic characteristics of the FPGA; Scheduling tasks on Reconfigurable  FPGA reconfiguration capabilities; FPGA architectures  Timing analysis for reconfigurable FPGA platforms;  Kernel mechanisms to support reconfigurable Mauro Marinoni systems. ReTiS Lab, TeCIP Institute Scuola superiore Sant’Anna - Pisa 1 2 Component-Based Software Design – LMES Component-Based Software Design – LMES Definition  A field-programmable gate array ( FPGA ) is an integrated circuit designed to be configured by a customer or a designer after manufacturing – hence "field-programmable". The FPGA configuration is generally specified using a hardware description FPGA language ( HDL ). Overview 3 4 Component-Based Software Design – LMES Component-Based Software Design – LMES Characteristics of the CLB General structure  These blocks contain the logic for the FPGA. It contains:  2-D array of logic blocks with electrically programmable  enough logic to create a small state machine interconnections  RAM enough for creating arbitrary combinatorial logic functions,  They provide: also known as lookup tables (LUTs)  Configurable logic blocks (CLB)  flip-flops for clocked storage elements  Connection lines  multiplexers in order to route the logic within the block and to and from external resources  Interconnection matrixes  Custom blocks  User can configure:  Intersections between logic blocks  The function of each block 5 6 Component-Based Software Design – LMES Component-Based Software Design – LMES 1

11/05/2016 Pros and Cons Performances  Advantages  FPGAs excel at computing non-data dependent algorithms in  Performance: Online analysis of high-rate data streams parallel .  Reliability: Deterministic hardware dedicated to every task  Customizable data path and ALU allow very large amounts  Reconfigurability: Nonrecurring engineering expenses of data to be transferred and computed within several clock  Durability: Radiation Hardened and Program Integrity cycles.  Time to market: Flexible and rapid prototyping and debugging  Despite lower clock frequencies , FPGA’s can outperform  Drawbacks conventional CPU’s on certain data processing tasks  Lower working frequencies  Higher power consumption  Higher cost 7 8 Component-Based Software Design – LMES Component-Based Software Design – LMES Integration with microprocessors Programming technologies  Fuse and anti-fuse:  In order to provide an execution environment to those  fuse makes or breaks link between two wires tasks not fitted for the FPGA execution paradigm  smaller and faster  Soft-core : a microcontroller wholly implemented inside the  one-time programmable FPGA ( NIOS II )  Flash:  System on Chip (SoC) : integrates a microcontroller and an  high density FPGA inside a single chip ( Zynq )  dedicated production process ( in the past… )  RAM-based:  memory bit controls a switch that connects/disconnects two wires  can be programmed and re-programmed easily (using bitstreams)  standard technology  volatile SRAM memory 9 10 Component-Based Software Design – LMES Component-Based Software Design – LMES RAM-based programming  Initially seen as a drawback imposing an initialization phase  the volatility of SRAM-based FPGAs is not a liability , but was in fact the key to many new types of RECONFIGURABLE applications. COMPUTING  the programming of such an FPGA could be changed by a completely electrical process… Characteristics 11 12 Component-Based Software Design – LMES Component-Based Software Design – LMES 2

11/05/2016 FPGA reconfiguration Selecting a Target FPGA Characteristics of the different reconfiguration approaches:  While the previous uses of FPGAs still treat these  Granularity chips purely as methods for implementing digital logic , the reprogrammability of modern FPGAs allows  Dynamic reconfigurability to download algorithms onto the FPGAs and change  Partial vs Full reconfiguration these algorithms just as general-purpose computers  Reconfiguration time can change programs. “Fine-grain Dynamic Partial Reconfigurable devices” 13 14 Component-Based Software Design – LMES Component-Based Software Design – LMES Granularity Dynamic reconfigurability Two main architectures:  It is the ability of a FPGA to modify operation during runtime  Course grained : consists of small number of large logic blocks  The primary advantages of runtime reconfiguration in devices  Small bitstream is required to configure them (low config. time)  Power/Size/Cost Reduction  Faster because of easy routing  Hardware reuse and flexibility  Less complexity and less flexibility  Application Portability  Fine grained : consists of large number of small logic blocks  Customization at the bit level => Greater flexibility & more complexity  The disadvantage of dynamic reconfiguration  Large bitstream is required to configure them (high config. time)  Suffer from the time needed to load the configuration bitstream before starting its execution  Easy conversion to ASIC  Less speedy 15 16 Component-Based Software Design – LMES Component-Based Software Design – LMES Partial vs Full reconfiguration Partial Reconfiguration  Partial reconfiguration (PR) allows  Partial Reconfiguration (PR) allows the ability to reconfigure a the ability to reconfigure a portion portion of an FPGA of an FPGA ICAP Module A Controlling Agent  It allows for critical parts of the design to continue operating while Mem controller Module B  Real advantages arise when PR is Central done during runtime also know as loading a partial design into a reconfigurable module dynamic partial reconfiguration Module C  Reconfiguration time of partial reconfiguration is much smaller  Dynamic Reconfiguration allows (~4-5 ms) than full reconfiguration(~12 ms) Module D the reconfiguration of a portion of an FPGA while the remainder  Wide variety of dynamically reconfigurable FPGA devices continues operating without any Static modules Reconfigurable Modules (PRMs) loss of data available in the market offer PR today  Two types of Regions  Lattice ORCA Architecture Modules: A & B FPGA PRR 1  Static – Keeps operating Static region  Atmel AT40K Architecture  Reconfigurable – Can be  AItera APEX 20K reconfigured with a new module Static PRR 2 Modules: C & D modules  Xilinx Virtex FPGAs 17 18 Component-Based Software Design – LMES Component-Based Software Design – LMES 3

11/05/2016 Partial Reconfiguration - Timing How to choose the FPGA model?  Exploitation of Partial Reconfiguration for a design requires significant knowledge on targeted device  An evaluation of the performance and limitations of your selection is required  Also the support provided by design tools must be evaluated  Correct FPGA selection matters!  Xilinx’s FPGA’s (the Virtex Family is a widespread solution) is chosen as the example FPGA 19 20 Component-Based Software Design – LMES Component-Based Software Design – LMES Xilinx Virtex-II/Pro Architecture Basic Xilinx FPGA Layout  Composed of a fine-grain 2D heterogeneous array that includes  Configurable logic blocks (CLBs)  Memory blocks (BRAMs)  DSP units (MULTs) Embedded Processor  I/O blocks (IOBs) (PowerPC/MicroBlaze)  FIFOs buffers Processor Local Bus  Each CLB contains LUTs, FFs, Gates & Multiplexers that can be configured to implement any design efficiently. On-Chip Peripheral Bus  This 2D array can configured either externally or internally. Internal Configuration Acces Port 21 22 Component-Based Software Design – LMES Component-Based Software Design – LMES Xilinx FPGA Layout – Inside CLBs Xilinx Virtex – Reconfiguration  FPGA is reconfigured by writing bits into Configuration Memory (CM).  CM is arranged in vertical frames (1bit wide) stretching from top to bottom. bit bit_b word  So Configuration data is organized into frames that target specific areas of the FPGA through frame addresses. 6T SRAM CELL  To reconfigure any portion of that frame the partial bitstream contain configuration data for a whole frame. 23 24 Component-Based Software Design – LMES Component-Based Software Design – LMES 4