Prototyping with a bio-inspired reconfigurable chip
Contents
1. POETIC The informa tion provided is the sole responsibility of the authors and does not reflect the Community s opinion The Community is not responsible for any use that might be made of data appearing in this publication The Swiss participants to this project are supported under grant 00 0529 1 by the Swiss government References 1 http www model com products default asp 2 http users ece gatech edu hamblen book wintim 3 ARM AMBA Specification Rev 2 0 Advanced RISC Machines Ltd ARM http www arm com armtech AMBA_Spec 1999 4 J Eriksson O Torres A Mitchell G Tucker K Lindsay D Halliday J Rosenberg J M Moreno and A E P Villa Spiking neural networks for reconfigurable POEtic tissue In A Tyrrell P Haddow and J Torresen editors Evolvable Systems From Biology to Hardware Proc Sth Int Conf on Evolvable Hardware ICES 03 volume 2606 of LNCS pages 165 173 Berlin 2003 Springer Verlag 5 D Hanson and C Fraser A Retargetable C Compiler De sign and Implementation Benjamin Cummings Publishing Company 1995 6 J Holland Genetic algoritms and the optimal allocation of trails In SIAM Journal of Computing volume 2 2 pages 88 105 1973 7 K TEAM S A Khepera User Manual Pr verenges Switzer land http www k team com 8 D S Linden Optimizing signal strength in situ using an evolvable antenna system In A Stoica J Lohn R Katz D Keymeulen and R S2. makes it an ex cellent tool for various other applications 6 Conclusion We have presented the POEtic chip a new reconfigurable circuit with an embedded microprocessor We have shown its usefulness for bio inspired systems and described fea tures which are important for the rapid prototyping of var ious applications The different software tools currently available have been described showing the ease of use of this new circuit In the near future the microprocessor tools and the or ganic subsystem tools will be merged in order to allow rapid tests of systems that involve both the microproces sor and a reconfigurable part using the entire POEtic tis sue For these systems a total VHDL simulation could be performed involving the VHDL description of both parts As an alternative the processor emulator will be linked to the VHDL simulation of the organic subsystem to give an excellent visualization of the microprocessor and molecule states This new tool will allow the rapid creation and test of new designs for POEtic without any need for a real cir cuit When the final chip is available the new tool will be used to visualize the state of the real circuit showing the molecules and the routing units state gathered by communi cation with the microprocessor 6 1 Acknowledgements This project is funded by the Future and Emerging Tech nologies programme IST FET of the European Commu nity under grant IST 2000 28027
3. 00000000 k03 00000000 00000004 EC000008 MOVEL RO H 84 kade doooooodi BoE Ad00o0do 00000005 54000000 CALL RO R06 00000000 RO 00000000 00000006 95440100 ADDI RLO R1O0 H 100 Ros oooo0000 ROS 00000000 00000007 C8000007 JUMPrI H 7 Dio Gbodait Rir 00000000 00000008 95440001 ADDI R10 R10 H 1 ni DDODODOO meai ADDI B10 RLO ESL R14 00000000 O x 00000000A 95440001 ADDI R10 R10 H 1 P16 00000000 FrrrrFES FFFFFFFF FFFFFFFY FFFFFFFF FFFFFFFF O000000B 95440001 ADDI R10 R10 H 1 R18 00000000 FFFFFFEC FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF oo00000C 60000000 RET R20 00000000 FFFFFFFO FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF 0000000D ECZOFFFF MOVEL R1 H FFFF R22 00000000 FFFFFFF4 FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF QODOUNOE AAAOVOAE ADD RZ RO RL R24 00000000 FFFFFFFS FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF 00000000F ECOOFFFF MOVEL RO HSFFFF R26 00000000 FFFFFFFC FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF 00000010 EC308000 MOVEH RL H 8000 R28 00000000 00000000 EC041000 C8000003 00000008 ED400100 00000011 14400001 ADD R2 RO R1 R30 00000000 00000004 EC000008 54000000 95440100 C8000007 ROORAUAS ECLOGONA RU ER RO H 8000 00000008 95440001 95440001 95440001 95440001 POPOTNE BESOg oes MOVEL R1 H 1 0000000C 60000000 ECZOFFFF 14400001 ECOOFFFF 00000014 14400001 ADD RZ RO RI 00000010 EC308000 14400001 EC108000 EC200001 DECOYS TS ECHONGDL MOVEL RO HS1LS 00000014 14400001 Ecooooo1 EC308000 14400001 l 00000018 EC000000 ECZ00001 18400001 18410000 oo0000
4. POEtic can be used as a platform for evolvable hardware repro ducing the work of Thompson 15 in a faster man ner A very fast way of evolving the configuration stream of POEtic has been developed 13 and will be tested with the chip as soon as it is available Com pared to commercially available FPGAs POEtic will be the best solution for solving these kind of prob lems for two reasons Firstly the microprocessor on the same chip as the reconfigurable array can rapidly change the configuration Secondly the implementa tion of the molecules being based only on multiplex ers allows unconstrained evolution by ensuring that short circuits cannot occur e As a third example on the Epigenetic axis a new kind of spiking neuron defined in 4 is currently being mapped to the molecules of POEtic These neurons have learning capabilities and are capable of taking care of a robot navigation task by recognizing ver tical lines with a linear camera A single neuron has now been tested and will serve to create a neural net work The routing layer a feature that does not exist in common FPGAs will serve to connect neurons to gether and the microprocessor will be used to evolve neuron parameters such as synaptic weights These three examples show the potential of POEtic as a prototyping platform for bio inspired systems Further more its on chip microprocessor with access to the con figuration bits of the reconfigurable array
5. Zebulum editors The 2002 NASA DoD Conference on Evolvable Hardware pages 147 151 Alexandria Virginia 15 18 July 2002 Jet Propulsion Laboratory California Institute of Technology IEEE Com puter Society 9 D Mange M Sipper A Stauffer and G Tempesti Towards robust integrated circuits The embryonics approach In Pro ceedings of the IEEE volume 88 4 pages 516 541 April 2000 10 J M Moreno Y Thoma E Sanchez O Torres and G Tem pesti Hardware realization of a bio inspired POEtic tissue In Proc 2004 NASA DoD Conference on Evolvable Hard ware Seattle USA To be published 11 D Roggen and Y Thoma An evolving and developing cel lular electronic circuit In Ninth International Conference on the Simulation and Synthesis of Living Systems ALIFE9 Boston Massachusetts USA To be published 12 E Sanchez D Mange M Sipper M Tomassini A Perez Uribe and A Stauffer Phylogeny ontogeny and epigenesis Three sources of biological inspiration for softening hard ware In T Higuchi M Iwata and W Liu editors Evolv able Systems From Biology to Hardware volume 1259 of LCNS pages 33 54 Berlin 1997 Springer Verlag 13 Y Thoma and E Sanchez A reconfigurable chip for evolv able hardware In Proc Genetic and Evolutionary Computa tion COnference GECCO 2004 Seattle USA To be pub lished 14 Y Thoma E Sanchez J M Moreno Arostegui and G Tem pesti A dynamic routing algor
6. in order to make their purpose clear These user defined components can then be used in other schematics allow ing a library of useful components to be constructed and re used The schemed editor figure 7 consists of two main parts the front end which handles the graphical user interface and the back end which can convert high level schematics into molecules The front end is written in C using the wx Widgets class library It presents a typical schematic editing interface with which users can connect components using wires The various properties of the components e g number of a schemed Schematicl modifi ae File Edit Tools Window Help x E x O E MM eE Molecule Choose E a p Figure 7 A schematic editor allows the rapid creation of designs which can then be ex ported as a molecular structure bits in a counter number of inputs to a logic gate can be set up using dialogue boxes Schematics can be saved and loaded in a simple text based format The back end has the task of taking a set of components and interconnections and generating the appropriate PO Etic molecules The process can be divided into five stages simplification logic synthesis component synthesis place ment and routing Firstly the schematic is simplified in some basic ways Groups of components are expanded into their constituent parts Connections between other connections are simpli fied s
7. not adjacent to one another It is composed of eight mul tiplexers two in each direction Each multiplexer can se lect from the two signals coming from each direction the output of the molecule or a second output The second out put is in most cases the inverse of the first The switch box has been designed with multiplexers rather than with anti fuse or RAM bits in order to avoid any short circuit This feature means that a developer can use POEtic as platform for evolvable hardware without any risk as no randomly generated bitstream configuration can destroy the chip The molecule can act in different operating modes fig ure 3 e In 4 LUT mode the output is any function of the four inputs e In 3 LUT mode two outputs are computed each from any 3 input function e In Comm mode the LUT is split into a 8 bit shift reg ister and a 3 input LUT e In Memory mode the LUT is used as a 16 bit shift register and can be used to implement a serial access memory e In Input mode the molecule retrieves a value from the dynamic routing layer e In Output mode the molecule sends a value to the dy namic routing layer e In Configure mode the molecule can partially recon figure a neighbouring molecule e In Trigger mode the molecule serves as a trigger to synchronize the dynamic routing process Figure 3 3 bits define the ope
8. to self repair without any global control Some artificial systems for example the embryon ics project 9 use the same principles to make an artificial organism out of many identical cells that can differentiate and self repair On the Epigenetic axis E we find the learning capabil ities of living beings based on neural networks Our brain or even a fly s brain is capable during its life of acquiring a lot of experience Furthermore these learned experiences have an effect on the organism s behaviour Artificial neural networks 17 are based on these principles and their pur pose is to develop systems that can for example learn to execute a task or recognize a pattern There has been considerable research involving one or more of these three life axes Most of it is done in software due to the lack of a real hardware platform specifically de signed for such applications However hardware implemen tations can dramatically improve the speed of genetic algo rithms evolvable hardware and neural networks by taking advantage of the inherent parallelism of hardware systems The POEtic 12 chip 10 is a new reconfigurable hard ware platform for rapidly prototyping bio inspired systems that employ POE principles In this paper we describe three applications which take advantage of the special features of POEtic to show its potential for prototyping These special features can be summarized as e combination of a micropr
9. 01C EC108000 ECZ00001 18400001 18410000 00000020 EC1O FFF ECZ00001 18400001 18410000 00000024 F0000000 F0000001 F0000002 F0000003 00000028 F0200004 F4400003 F4400002 F4400001 00000002C 70630002 FO84001F FOASOO1F D00A0000 00000030 00000000 00000000 00000000 00000000 00000034 00000000 00000000 00000000 00000000 00000038 00000000 00000000 00000000 00000000 0000003 oooo0000 oooooo00 ooooo000 ooooooo0 E gt ix counter 6 Start Size Type Info 00000000 00000400 ROM lt internal gt 00000400 O0001C00 RAM lt internal gt 00002000 00000010 DLL MSVC Basic DLL 00002010 00000010 DLL MSVC counter DLL MSVC print DLL 1156 instruction sec Figure 4 The emulator showing assembler code the registers and the memory con tents 4 The Design Tools Creating a design for the molecular array is a more diffi cult task than compiling a C program for the microproces sor Development tools are an important way of easing the task of designing a molecular array A program called PO EticMol allows creation of designs at the molecular level and visualization of the system during a simulation while a schematic editor lets the developer create designs at the gate level ioi xl File Edit wiew Project Tools Window Help la x OSA LBAS Figure 5 The graphical user interface of POEticMol showing the configuration of 6 molecules 4 1 Molecular Design POEticMol provides a graphical inte
10. 3 allows communication with all in ternal elements as shown in figure 1 as well as with external devices It also permits the interconnection of many POEtic chips in order to realize a bigger virtual reconfigurable array The microprocessor can configure the array and also re trieve its state Access is made in parallel so configuration and partial reconfiguration are very fast The retrieved state can be used to calculate the fitness of an individual in the case of an evolutionary process or simply to debug any de sign running on POEtic For genetic algorithms evolution can be performed by the microprocessor This obviates the need for slow data transmission to and from a host com puter 2 2 The Reconfigurable Array The organic subsystem is composed of two layers the molecular layer that is reconfigured by the microprocessor and the routing layer which implements a dynamic routing algorithm managed by the molecules The molecular layer is a grid of basic elements called molecules Although being similar to standard FPGA ele ments molecules have special features which are useful for bio inspired systems The main components are a 4 input look up table a flip flop and a switch box as depicted in figure 2 Figure 2 On the left 9 molecules of the re configurable array In the centre a molecule in 4 LUT mode On the right the switch box of a molecule The switch box allows the connection of molecules that are
11. Etic chip s architecture is general enough for the implementation of any type of application that needs a microprocessor to communicate closely with a reconfig urable array However the applications that have been de veloped for the POEtic chip thus far are all bio inspired sys tems We now go on to briefly describe three of these appli cations e A PO tissue 11 that brings Phylogenetic and On togenetic mechanisms into play has already been de signed for the POEtic chip Its purpose is to use a ge netic algorithm to evolve a cellular system where ev ery cell can act as a 3 input function Evolution deals with the cells functionality and with the connectiv ity by exploiting the dynamic routing capabilities of the circuit Evolution is done by the microprocessor while the ontogenetic part that is the development of the system starting from a single cell is executed in the organic subsystem This application takes advan tage of the dynamic routing so that the organism can grow the partial reconfiguration to differentiate cells and of the rapid communication between the micropro cessor and the reconfigurable array three features not present in commercial FPGAs e Evolvable hardware EHW on the Phylogenetic axis deals with the design of analog or digital circuits us ing genetic algorithms This technique replaces the de sign engineer with an algorithm and can be used in many different areas e g robot control
12. Prototyping with a bio inspired reconfigurable chip Yann Thoma and Eduardo Sanchez Logic Systems Laboratory Swiss Federal Institute of Technology of Lausanne EPFL Lausanne Switzerland yann thoma epfl ch eduardo sanchez epfl ch Carl Hetherington Dept of Electronics University of York York UK cthl103 ohm york ac uk Abstract In this paper we explain how the POEtic chip can be used for rapid prototyping The POEtic chip currently in the test phase is a system on chip SoC containing a microproces sor and a reconfigurable array Special features allow the dynamic creation of data paths in the reconfigurable array at runtime It has been specially designed to ease the de velopment of bio inspired systems such as neural networks but can serve as a general purpose platform or as a pro totype for hardware software codesign An AMBA bus al lows POEtic chips to be connected to each other or to ex ternal devices After describing the hardware SoC we dis cuss the software tools that have been created to design and test different applications Three of these applications are described in order to demonstrate the utility of the POEtic chip s special features 1 Introduction In recent years bio inspiration has been more and more important in the design of electronic and software systems Artificial neural networks take care of sorting mail by ana lyzing human handwriting 16 while new antenna shapes are develop
13. ecules have been placed on the tissue the last step is to implement their interconnections using the switch boxes that are a part of each molecule A connection be tween two molecules is constructed using Dijkstra s short est path algorithm and the switch boxes on the path are con figured appropriately At present there is no optimisation or re try step if rout ing fails Such techniques are currently under development The result of the synthesis is a set of molecules which are written to disk in the format used by POEticMol This tool can then be used to view the results of the schemed synthe sis 4 3 Simulation The test phase is a crucial part of any system design al lowing developers to find and fix errors POEticMol simu lates the entire organic subsystem using its VHDL descrip tion This description has been used to create the electronic layout of the final chip and so reflects exactly the real chip behaviour Figure 8 shows every component involved in a simu lation software DLLs files Modelsim a digital designs simulator is launched by POEticMol and simulates the or ganic subsystem A Foreign Language Interface supplied by Modelsim allows the VHDL code to be interfaced with a windows DLL written in C or C Using this mechanism we defined a special component POEticvhdl dll which in terfaces the simulation and the graphical user interface of POEticMol using a pipe file The simulation and the GUI can th
14. ed using genetic algorithms 8 Designers can draw inspiration from the three life axes Phylogeny evo lution Ontogenesis development and Epigenesis learn ing The Phylogenetic axis P represents the way in which species evolve and how parents share their genetic heritage to create a new individual The neo Darwinian theory is now used by developers to solve complex problems for which no Daniel Roggen Autonomous Systems Laboratory EPFL Lausanne Switzerland daniel roggen epfli ch Juan Manuel Moreno Dept of Electronic Engineering Technical University of Catalunya UPC Barcelona Spain moreno eel upc es deterministic method can be found Genetic algorithms 6 are based on a selection from a population of individuals representing potential solutions using a fitness function de pending on the problem being solved The selected individ uals share their genotype to create a new generation by ap plying cross over and mutation The process is repeated un til an acceptable solution is found The Ontogenetic axis O corresponds to the develop ment of an organism from its first cell the zygote and to the self healing capabilities of living beings No machine or computer is capable of the self repair seen in nature al though such a capability would be very useful for many sit uations such as space exploration where humans cannot intervene In a real organism every cell contains the en tire genome allowing cells
15. erefore communicate with the GUI controlling the simulation and retrieving its state Inputs Outputs to the simulation are controlled by a sep arate DLL called POEticio dll that can be rewritten by the developer It allows the forcing of inputs and the re trieval of outputs in order for example to interface with another piece of software like a robot simulator or to write data into a file A DLL function is called every clock cy cle allowing the control of inputs outputs with high level functions supplied by the programmer During a simulation the GUI displays the state of the molecules and routing units either together or separately In this way the developer has a global view on the entire system either step by step or after any number of clock cy cles Furthermore if the design has been developed with the schematic editor a pipe file allows the DLL loaded by Mod elsim to send simulation values to the schematic In this Depends on the application Schematic Editor General architecture for simulation o Figure 8 The different programs and files in volved in the simulation process In this ex ample the VHDL simulation is linked to a Khepera robot 7 simulator and schematic editor using pipe files way the user can visualize the molecule states correspond ing to the higher level design s state 5 Applications Although specially designed for bio inspired cellular ap plications the PO
16. in understanding the processor architecture As the simulator only displays signals in a chronogram its usefulness is reduced when simulating complex pro grams Therefore after the VHDL model of the CPU was frozen a CPU emulator was designed figure 4 It executes CPU programs using a software model which decodes in structions one by one and updates the variables represent ing the CPU state registers memory content etc accord ingly The CPU programs execute faster when the CPU is emulated because the emulator does not resort to the more complex VHDL models Speedups compared to the VHDL simulation of the order of 10 to 100 were observed even though the emulator is not fully optimized The emulator provides a graphical user interface which shows the status of the CPU The code window shows the instructions in the program memory together with their op codes and the corresponding comments that were placed in the source assembler file Breakpoints can be set and the code executed line by line or continuously until either a breakpoint is reached or the execution is stopped manu ally The register window and the memory window show the content of the registers and the CPU memory highlight ing the entries which have been changed by the execution of an instruction The current version of the emulator can import output files from the WinTim32 meta assembler and support for the LCC meta compiler will be added in the near future The e
17. ithm for a bio inspired re configurable circuit In P Y K Cheung G A Constan tinides and J T de Sousa editors Proc of the 13th Inter national Conference on Field Programmable Logic and Ap plications FPL 03 volume 2778 of LNCS pages 681 690 Berlin Heidelberg 2003 Springer Verlag 15 A Thompson On the automatic design of robust electron ics through artificial evolution In M Sipper D Mange and A P rez Uribe editors ICES 9S volume 1478 of Lecture Notes in Computer Science pages 13 24 Berlin Heidelberg 1998 Springer Verlag 16 L S Yaeger J B Webb and R F Lyon Combining neural networks and context driven search for online printed hand writing recognition in the newton A I Magazine 19 1 73 89 1998 17 J Zhu and P Sutton FPGA implementations of neural net works a survey of a decade of progress In P Y K Cheung G A Constantinides and J T de Sousa editors Proc of the 13th International Conference on Field Programmable Logic and Applications FPL 03 number 2778 in LNCS pages 1062 1066 Berlin Heidelberg Springer Verlag
18. mulator can export the program in a VHDL ROM file for subsequent verification using VHDL simulation Export in the COE format which is used by the Xilinx memory synthesis tools is also supported and can be used to initial ize the content of the program ROM when synthesizing the CPU on an FPGA Plugins in the form of DLLs can be included to emu late memory mapped peripherals When the CPU reads or writes memory locations which correspond to the address space of a plugin the corresponding functions of the DLL are called This offers the opportunity to emulate peripher als of the SoC without modifying the emulator In this way a peripheral emulating an UART Universal Asynchronous Receiver Transmitter has been implemented When char acters are written to its memory address they are displayed in the console of the emulator This is a convenient way of displaying program information from the assembler code in a way which is fully compatible with a SoC using a real UART Further DLLs have been written to interface the em ulator with the molecule design tools described in the next sections These DLLs allow simultaneous execution of CPU programs and molecular hardware z zio xi E r gt e _cooo0000 EC041000 MVSPL H 1000 PC 00000009 IM 00000000 SP 00001001 LFSR 00000000 00000001 C8000003 JUMPrI H 3 enc gODODONUOS Or cas Se o Heo 00000002 00000008 NOP ROO 00000008 ROl 00000000 00000003 ED400100 MOVEL R10 H 100 aS
19. n E sel_n0 s_in0 x gt i ay seLinputl dinw selmi win0 C Memory sel_input2 dff_out v sel_e0 w_in0 v dff_enable none si sel_el w_inl T C Communication C Input C Output Trigger Others sel_s0 n_in0 ed z vV Reset Value t Gonhgure sel_s1 none v won l Sequential output V Rising Clock Edge sel_w0 Je ind x Partial reconfiguration LUT DFF enable from neighbor sel_w1 func_lout w Global enable disabled LUT mus inputs SwitchBox Contig input north v Mode Local Reset none Others DFF reset Asynchronous Change Color Group developme Comment o Default values LUT LUT content 0000111101111111 C Synchronous Most significant bit on the left Figure 6 The dialog in which the user can de scribe the entire molecular configuration ray of POEtic molecules to implement a particular circuit The molecular array is passed to the POEticMol tool from which the synthesized molecules can be examined and sim ulated in the normal way In addition schemed collects the results of any simulations that are run and presents the re sults on the schematic Schemed also presents some other useful tools for schematic designers Firstly a set of components and in terconnections can be grouped together into a new user defined component Such a component might be a de sign for a simple neuron for example The inputs and outputs of this new component can be named as appropri ate
20. nnected to other cells by means of this mechanism As the path creation is made at runtime and can be made incrementally POEtic is a very good ar chitecture on which to grow neural networks or any other system involving a changing topology The hardware circuit having been presented we now look at the development tools for the microprocessor and the organic subsystem 3 The Processor Tools The first of the processor tools is an assembler which has been written to test the microprocessor design Like ev ery assembler it translates an ASCII description to machine code in a simple manner It has been derived from the Win Tim32 meta assembler 2 The assembler although very useful for developing effi cient code and for testing the processor is not ideal for end users A C compiler derived from the LCC meta compiler 5 has been realized as an alternative The machine code generated by the assembler or the compiler can be run by either a simulator an emulator or by the real chip A VHDL description of the microprocessor has been used to create the electronic layout of the chip These VHDL files also serve to simulate the microprocessor when used with Modelsim 1 a tool to simulate and debug hard ware designs The machine code can be put into a VHDL file describing the processor ROM and compiled in Mod elsim The result of the simulation is a waveform which ex actly mimics the processor s signals and this can be helpful
21. o that all connections go between one component s output and another s input Secondly any logic gates within the circuit are collected together Logic gates are different from most other compo nent types in that several gates can be synthesized using a single POEtic molecule all other component types require an integer number of molecules for their implementation The logic gates in the circuit are collapsed into the smallest suitable number of 4 input 1 output look up tables such LUTs can be synthesized directly into molecules The third step is to synthesize the molecules that are re quired for each component Each component type has an al gorithm to generate the required molecules and these algo rithms can be dependent on parameters of the component For example there are several different ways of implement ing a trigger component and the optimal implementation depends on the number of clock cycles that is required be tween trigger pulses Schemed can use the trigger length that the designer has specified in order to choose the opti mal trigger representation Following synthesis is the process of placing compo nents within the tissue Firstly components are topographi cally sorted based on their interconnections Then the ar rangement of molecules required for each component is found The required molecule arrangements are then laid out onto the tissue using a simple snake like placement al gorithm Once mol
22. ocessor and a reconfigurable array e parallel configuration e partial reconfiguration e dynamic routing The next section briefly describes the POEtic hardware platform Section 3 discusses the microprocessor program ming tools while section 4 describes the reconfigurable hardware development tools We then show some applica tions that are currently being developed on this platform before concluding 2 The POEtic Platform The POEtic chip has been specifically designed to ease the development of bio inspired applications It is com posed of two main parts a microprocessor in the environ mental subsystem and a 2 dimensional reconfigurable ar ray called the organic subsystem figure 1 This array is made of small elements called molecules that are essen tially composed of a 4 input look up table and a flip flop Although being oriented for bio inspired systems its ar chitecture makes it a good candidate for any general design as the microprocessor can access the reconfigurable array very rapidly This can be useful for both configuration and state retrieval A test chip containing the microprocessor and twelve molecules is currently being manufactured This ASIC pro totype uses a CMOS 0 35 um 1P 5M technology Based on this prototype the final chip will be designed and then real ized 2 1 The Microprocessor The microprocessor is a 32 bit RISC processor specif ically designed for the POEtic chip Its purpose is
23. rational mode of a molecule On the left a molecule in 4 LUT mode On the right a molecule in 3 LUT mode One of the special features of the reconfigurable array is that molecules can be partially reconfigured without mi croprocessor intervention A molecule configuration is de scribed by 76 bits split into 5 blocks The molecule can allow a reconfiguration of each of its blocks and chooses the source of the configuration data A partial reconfigura tion is processed when a molecule in Configure mode is ac tive this is when its first input is active In this state config uration bits are shifted on every clock cycle with the sec ond input of the Configure molecule being sent out as the new configuration bitstream This feature allows LUT con tent or dynamic routing addresses to be changed at runtime It can be very useful for self repair systems in which the ar ray can partially reconfigure itself without needing an exter nal agent The routing layer is a grid of routing units which can dy namically create paths between different points of the cir cuit at runtime It implements a distributed dynamic rout ing algorithm based on addresses interested readers can see a description of this algorithm in 14 It can be used to create connections between any parts of the circuit by us ing the input output molecules In a cellular system e g a neural network for instance cells could be identified by a unique ID and then co
24. rface figure 5 for configuration of the molecules by hand The user sees all the molecules and can specify every configuration option via a dialog figure 6 In addition molecules can be grouped in order to ease the visualization of complex systems The inter molecular communication is done through switch boxes and manual configuration of these switch boxes would be tedious A basic router has been in corporated which requires the developer only to click on a source and a target A path is automatically cre ated through the switch boxes using a breadth first search algorithm to find the shortest path between the two points Initially POEticMol was conceived as a prototype to ease the debugging phase of the organic subsystem It was a good tool to visualize the state of the molecules and rout ing units and has changed a lot since the first version of the chip Now that the chip is fixed it is widely used to cre ate new designs 4 2 Schematic Editor The POEticMol tool presents the designer with a low level view of the POEtic IC An additional tool schemed offers the option of a higher level design process Rather than operating in terms of molecules the front end to schemed allows users to draw circuits based on a col lection of high level components such as counters trig gers and logic gates The software can then synthesize an ar Molecule Properties x Mode LUT inputs Switch Box C ALUT sel_input0 config i
25. to con trol the organic subsystem including the configuration of molecules as well as to execute evolutionary processes During the design process particular attention was paid to the microprocessor size so as to leave more room for the re configurable array The main features of the POEtic microprocessor are as follows e The architecture is LOAD STORE POEtic tissue environmental subsystem organic subsystem processor system interface er ZS site fay Xe a E EA E S 7 booth ER E ee 16x16 multiplier PP V2 OL AD Figure 1 The POEtic chip showing the mi croprocessor and the reconfigurable array In the organic subsystem the molecular plane bottom is connected to the routing plane top Many elements connected to the AMBA bus another timer and serial and parallel ports are omitted in order to simplify the schematics e Every instruction is 32 bits e Every instruction is executed in one clock cycle e A five stage pipeline implements the datapath with the following states Fetch Decode Execute Memory and Writeback e 57 instructions are defined two of which give access to a hardware pseudo random number generator a read instruction and the load of an initial seed which can be very useful for evolutionary processes This gener ator has been implemented using a 32 bit linear feed back shift register e Up to 5 interrupt sources can be handled by the micro processor e An AMBA bus
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