Source: https://patents.google.com/patent/US10031733B2/en
Timestamp: 2019-04-25 17:18:29+00:00

Document:
A method for operating a system on a chip comprising a conventional processor unit (CISC, RISC, VLIW, DSP) and an array processor having a multidimensional arrangement of arithmetic units. Operation information for the array processor are stored in a memory shared between the conventional processor and the array processor. At runtime the conventional processor points the array processor to the memory area comprising the operation information. A management unit inside the array processor is autonomously loading the operation information into the array processor.
This application is a continuation of U.S. patent application Ser. No. 10/480,003, filed on Jun. 18, 2004, which is a national phase of International Application No. PCT/EP02/06865, filed on Jun. 20, 2002, which claims priority to German Patent Application No. DE 101 29237.6, filed on Jun. 20, 2001, the entire contents of each of which are expressly incorporated herein by reference thereto.
The present invention relates to data processing. In particular, the present invention relates to traditional, i.e., conventional and reconfigurable processor architectures as well as methods therefor, which permit translation of a classical high-level language (PROGRAM) such as Pascal, C, C++, Java, etc., in particular onto a reconfigurable architecture. The present invention relates in particular to integration and/or close coupling of reconfigurable processors with standard processors, data exchange, and synchronization of data processing.
A conventional processor architecture (PROCESSOR) is understood in the present case to refer to sequential processors having a von Neumann architecture or a Harvard architecture, such as controllers or CISC processors, RISC processors, VLIW processors, DSP processors, etc.
The term “reconfigurable target architecture” is understood in the present case to refer to modules (VPUs) having a function and/or interconnection that is repeatedly configurable, in particular configurable without interruption during run time, in particular integrated modules having a plurality of one-dimensionally or multidimensionally arranged arithmetic and/or logic and/or analog and/or memory modules, in particular also coarse-grained modules (PAEs) which are interlinked directly or via a bus system.
The generic class of such modules includes in particular systolic arrays, neural networks, multiprocessor systems, processors having a plurality of arithmetic units and/or logic cells, interlinking and network modules such as crossbar switches as well as known modules of the generic types FPGA, DPGA and XPUTER, etc. In this connection, reference is made in particular to the following patents and patent applications: P 44 16 881.0-53, DE 19781 412.3, DE 19781 483.2, DE 19654846.2-53, DE 19654593.5-53, DE 19704044.6-53, DE 19880 129.7, DE 19861 088.2-53, DE 19980312.9, PCT/DE 00/01869, DE 10036627.9-33, DE 10028397.7, DE 101 10530.4, DE 101 11 014.6, PCT/EP 00/10516, EP 01 102674.7, DE 19651 075.9-53, DE 19654846.2-53, DE 19654593.5-53, DE 19704728.9, DE 19707872.2, DE 101 39 170.6, DE 19926538.0, DE 101 42904.5, DE 101 10530.4. These are herewith incorporated to the full extent for disclosure purposes.
This system may be designed in particular as a (standard) processor or module and/or may be integrated into a semiconductor (system on chip, SoC).
Reconfigurable modules (VPUs) of different generic types (such as PACT XPP technology, Morphics, Morphosys, Chameleon) are largely incompatible with existing technical environments and programming methods.
Programs for these modules are typically incompatible with existing programs of CPUs. A considerable development expense is thus necessary for programming, e.g., in particular for modules of the generic types Morphics, Morphosys. Chameleon already integrates a standard processor (ARC) on more or less reconfigurable modules. This makes approaches for programming tools available. However, not all technical environments are suitable for the use of ARC processors; in particular there are often existing programs, code libraries, etc. for any indeterminate other CPUs.
In internal experiments it has been found that there are certain methods and program sequences which may be processed better using a reconfigurable architecture rather than a conventional processor architecture. Conversely, there are also such methods and program sequences which are better executed using a conventional processor architecture. It would be desirable to provide a sequence partitioning to permit appropriate optimization.
Conventional translation methods for reconfigurable architectures do not support any forwarding of codes to any standard compilers for generating object codes for any desired PROCESSOR. Ordinarily, the PROCESSOR is fixedly defined within the compiler.
In addition, there are no scheduling mechanisms for reconfiguring the individual configurations generated for VPUs. In particular there are no scheduling mechanisms for configuration of independently extracted portions or for individual partitions of extracted portions. Conventional corresponding translation methods are described in the dissertation Ubersetzungsmethodenjür strukturprogrammierbare Rechner [Translation Methods for Structure Programmable Computers], by Dr. Markus Weinhardt, 1997, for example.
Several conventional methods are known for partitioning array CODE” e.g., Joao M. P. Cardoso, Compilation of Java™ Algorithms onto Reconfigurable Computing Systems with Exploitation of Operation-Level Parallelism, Ph.D. dissertation, Universidade Tecnica de Lisboa (UTL), 2000.
However, these methods are not embedded into any complete compiler systems. Furthermore, these methods presuppose complete control of the reconfiguration by a host processor, which involves considerable complexity. The partitioning strategies are designed for FPGA-based systems and therefore do not correspond to any actual processor model.
An object of the present invention is to provide a method for a commercial application.
A reconfigurable processor (VPU) is thus designed into a technical environment which has a standard processor (CPU) such as a DSP, RISC, CISC processor or a (micro)controller. The design may be accomplished according to an embodiment of the present invention in such a way that there is a simple and efficient connection. One resulting aspect is the simple programmability of the resulting system. Further use of existing programs of the CPU as well as the code compatibility and simple integration of the VPU into existing programs are taken into account.
A VPU (or a plurality of VPUs, although this need not be mentioned specifically each time) is coupled to a preferred CPU (or a plurality of CPUs, although this need not be mentioned specifically each time) so that it assumes the position and function of a coprocessor (or a plurality of coprocessors that respond optionally). This function permits a simple tie-in into existing program codes according to the pre-existing methods for working with coprocessors according to the related art.
The data exchange between the CPU and VPU according to the present invention may be accomplished by memory coupling and/or IO coupling. The CPU and VPU may share all resources; in particular embodiments, it is also possible for the CPU and VPU to jointly use only a portion of the resources and to make other resources available explicitly and/or exclusively for a CPU or VPU.
To perform a data exchange, data records and/or configurations may be copied and/or written/read in memory areas particularly provided for those purposes and/or corresponding basic addresses may be set in such a way that these point to the particular data areas.
To control the coprocessor, preferably a data record which contains the basic settings of a VPU, e.g., certain basic addresses are provided, for example. In addition, status variables may also be provided for triggering and for function control of a VPU by a CPU and for acknowledgments from a VPU to a CPU. This data record may be exchanged via a shared memory (RAM) and/or via a shared peripheral address space (IO).
For synchronization of the CPU and VPU, unilaterally or mutually acting interrupt methods (which are implemented, for example, by signal transfer over interrupt lines and/or interrupt inputs that are specifically dedicated and/or designed for this purpose) and/or the synchronization is accomplished by polling methods. Furthermore, interrupts may also be used for synchronization of data transfers and/or DMA transfers.
In an example embodiment that is particularly preferred, a VPU is started by a CPU and thereafter operates preferably independently of the application.
A preferred design in which the VPU provides its own mechanisms for loading and controlling configurations is particularly efficient. The generic type of these VPUs include, for example, PACT XPP and Chameleon. The circuits according to the present invention permit a method of operation in which the configurations of the VPU are loaded into a memory together with the program to be executed by the CPU. During execution of the program, the CPU may refer the VPU to the memory locations (e.g., by giving the addresses or pointers), each containing configurations to be executed. The VPU may then load the configurations independently and without further influence by the CPU. The execution by the CPU starts immediately or optionally by means of additional information (e.g., interrupt and/or start instruction).
In a particularly preferred expansion, the VPU may read and write data independently within a memory.
In a particularly preferred expansion, the VPU may also independently load new configurations out of the memory and may perform new configurations as needed without requiring any further influence by the CPU.
These embodiments permit extensive operation of VPUs independently of CPUs. Only a synchronization exchange between CPU and VPU, which may preferably take place bidirectionally, is provided in addition to coordinate data processing operations and/or executions of configurations.
It has also been recognized that methods of data processing may and/or should preferably be designed so that particularly suitable portions (VPU code) of the program to be translated are identified and extracted for the reconfigurable target architecture (VPU) to permit particularly efficient data processing. These portions are to be partitioned accordingly and the time sequence configuration of the individual partitions is to be controlled.
The remaining portions of the program may be translated onto a conventional processor architecture (PROCESSOR). This is preferably accomplished in such a way that these portions are output as high-level language code in a standard high-level language (e.g., ANSI C) so that an ordinary high-level language compiler (optionally pre-existing) is able to process it without difficulty.
It should also be pointed out that these methods may also be used for groups of a plurality of modules.
In particular a type of “double buffering” may be used for a particularly simple and at the same time rapid reconfiguration in which a plurality of VPUs are provided, so that a portion of the VPUs may be reconfigured at a time when another portion is computing and perhaps yet another may be inactive, for example.
Data links, trigger links, status links, etc. are exchanged among a plurality of VPUs in a suitable way, and are optionally wired through addressed buses and/or multiplexers/demultiplexers according to the VPUs that are currently active and/or to be reconfigured.
One advantage of this method is that existing code which has been written for any processor, may continue to be used by involving a VPU, and no modifications or only comparatively minor modifications need be made. The modifications may also be performed incrementally, with more code being transferred gradually from the processor to the VPU. The project risk drops, and there is a significant increase in clarity. It should be pointed out that such a successive transfer of more and more tasks to the VPU, i.e., to the integral, multidimensional, partially reconfigurable and in particular coarse-grained field of elements, has a special meaning on its own and is regarded as being inventive per se because of its major advantages in system porting.
In addition, the programmer is able to work in his/her accustomed development environment and need not become adjusted to a novel and possibly foreign development environment.
A first aspect of the present invention may be seen in the fact that a PROCESSOR is connected to one or more VPUs so that an efficient exchange of information is possible, in particular in the form of data information and status information.
Importance may also be attributed to the configuration of a conventional processor and a reconfigurable processor so that exchange of data information and/or status information between same is possible during running of one or more programs and/or without having to significantly interrupt data processing on the reconfigurable processor and/or the conventional processor in particular; importance may also be attributed to the design of such a system.
d) other memory media (hard drive, flash ROM, etc.).
In principle, the VPU and/or the CPU may also independently access the memory without the assistance of a DMA. The shared memory may also be designed as a dual port memory or a multiport memory in particular. Additional modules may be assigned to the system, and in particular reconfigurable FPGAs may be used to permit fine-grained processing of individual signals or data bits and/or to make it possible to establish flexible adaptable interfaces (e.g., various serial interfaces (V24, USB, etc.), various parallel interfaces, hard drive interfaces, Ethernet, telecommunications interfaces (alb, TO, ISDN, DSL, etc.)).
The structure of a VPU is known, for example, from the patents and patent applications described above. Attempts to arrive at alternative module definitions have become known under the name Chameleon, for example. VPUs may be integrated into a system in various ways. For example, a connection to a host processor is possible. Depending on the method, the host processor may assume the configuration control (HOSTRECONF) (e.g., Chameleon) or there may be, for example, a dedicated unit (CT) for controlling the (re)configuration.
Accordingly, the translator according to the method described here generates the control information for the reconfiguration for a CT and/or a HOSTRECONF.
The translation principle may be embodied in such a way that by using a preprocessor, the portions that may be mapped efficiently and/or reasonably on the particular certain VPU(s) may be extracted from a PROGRAM via a PREPROCESSOR. These portions are transformed into a format suitable for VPUs (NML) and are then translated further into an object code.
The remaining code and/or the extracted code is expanded according to experience at or with respect to the location of the code portions that are missing due to the extraction, by adding an interface code which controls communication between PROCESSOR(s) and VPU(s) according to the architecture of the target system. The remaining code which has been optionally expanded may preferably be extracted. This may take place as follows, for example: . . . .
“II START EXTRACTION″ denotes the start of a code to be extracted.
″II END EXTRACTION″ denotes the end of a code to be extracted.
In such a case, the unit for implementation of the program in configuration codes is designed to recognize the hints and/or implementation instructions.
In this case, the unit for implementation is designed to tie NML program portions, i.e., program portions for execution in and/or on a reconfigurable array, into a larger program.
Alternatively and/or additionally, extraction from an object-oriented class is also possible. Macros suitable for a VPU are defined as a class in the class hierarchy o fan object-oriented programming language. The macros may be characterized by annotation so that they are recognized as codes intended for a VPU and are processed further accordingly—even in higher hierarchies of the language.
Within a macro, a certain networking and/or mapping is preferably predetermined by the macro which then determines the mapping of the macro onto the VPU.
Instantiation and chaining of the class results in implementation of the function which includes a plurality of macros on the VPU. In other words, instantiation and chaining of macros define the mapping and interconnection of the individual operations of all macros on the VPU and/or the interconnection and/or data exchange between the VPU and CPU, if necessary.
The interface codes are added in instantiation. Chaining describes the detailed mapping of the class on the VPU.
A class may also be formed as a call of one or more NML routines, for example.
Extraction by analysis is also possible. Portions within the PROGRAM which may be mapped efficiently and/or appropriately on the VPU are recognized using the analytical methods adapted to the particular VPU.
These portions are extracted from the PROGRAM.
An analytical method suitable for many VPUs, for example, is to create data flow graphs and/or control flow graphs from the PROGRAM. These graphs may then be analyzed automatically with regard to their possible partitioning and/or mapping onto the target VPU. In this case, the portions of the graphs generated and/or the corresponding PROGRAM PORTIONS, which may be partitioned and/or mapped sufficiently well, are extracted. To do so, a partitionability and/or mappability analysis may be performed, evaluating the particular property. Partitioning and extraction of the program portions on the VPU as well as the introduction of the interfaces provided are then performed according to this evaluation.
Reference is made here explicitly to the analytical methods described in German Patent Application DE 101 39 170.6 which may be used, for example. The aforementioned patent application is herewith incorporated to full extent for disclosure purposes.
One possible analytical method is also provided by recognition of certain data types.
Different data types are more or less suitable for processing on a VPU. For example, complex pointer arithmetics, i.e., pointer-based data addressing (pointer) is difficult to map onto a VPU, whereas arrays are very easily mappable.
Therefore, the particular suitable data types and at least essential portions of their data processing may be transferred largely automatically or manually to a VPU according to the present invention and extracted accordingly. The extraction is performed in response to the occurrence of certain data types and/or data operations.
It should be pointed out here that additional parameters assigned to the data types may provide additional information for determining the executability and/or execution performance on a VPU and therefore may also be used to a significant extent for extraction. For example, the size of the arrays to be computed plays a significant role. It is usually not worthwhile to perform computations for small arrays on a VPU because the resources needed for synchronization and data exchange between the CPU and VPU may be excessive. However, it should again be pointed out that small arrays for which computations are performed particularly frequently within a loop are nevertheless very suitable for VPUs if the loop is computed almost completely on the VPU. Large arrays, however, may usually be computed particularly efficiently on a VPU.
In addition, it should be pointed out that certain data types may be created by a specially adapted compiler or, optionally, by a user (e.g., by using TYPE in Pascal), these being particularly suitable for VPUs and data processing of which is then executed on a VPU.
The term “stream” defines a data stream usually of a great, possibly not previously known, and/or infinite, length. Stream1 here had a length that was not previously known. For example, an FIR filter programmed with this type of data (or, for example, an FFT or DCT) could be mapped automatically onto a VPU—and optionally rolled out. The reconfiguration is then typically and preferably performed in response to other mechanisms than the data stream, e.g., by counters, comparators, CT-controlled and/or by timeout. For example, if wave configuration or some other reconfiguration is to be triggered here, then this characterization of a data packet, in particular data bytes, prompted via conventional methods may be the last to take place to trigger the reconfiguration after and/or with the run-through of this data packet, which is characterized as the last data packet.
stream2 defines a data stream having the length of 256 bytes here, which may be treated like stream1, but has the property of ending after 256 bytes and thus possibly triggering a reconfiguration after the end in the sense of the patents cited above by the same applicant. In particular a wave reconfiguration, e.g., according to DE 19704728.9, DE 19926538.0, DE 10206857.7, DE 10028397.7 may be triggered with the occurrence of the last data byte and the particular PAE processing the byte may be reconfigured with the processing of this last data byte.
A translation of the extracted code according to NML which is suitable for the implemented VPU may preferably be performed.
For data flow-oriented VPUs, a data flow graph and/or a control flow graph may be created automatically, for example. The graphs are then translated into NML code.
Corresponding code portions such as loops may then be translated via a database (lookup) or ordinary transformations may be performed. For code portions, macros may also be provided and are then used further according to the IKR disclosed in the aforementioned patent applications.
Modularization according to PACT13 (PCT/DEOO/01869), FIG. 28 may also be supported.
Optionally, the mapping and/or its preparation may already take place on the VPU, e.g., by performing the placement of the required resources and routing the connections (place and route). This may be done, for example, according to the conventional rules of placement and routing.
It is also possible to analyze the extracted code and/or the translated NML code for its processing efficiency by using an automatic analytical method. The analytical method is preferably selected so that the interface code and the performance influences derived from it are also included in the analysis at a suitable point. Suitable analytical methods are described, for example, in the patent applications by the present patent applicant as cited above.
The analysis is optionally performed via complete translation and implementation on the hardware system by executing the PROGRAM and performing measurements using suitable conventional methods.
It is also possible that, based on the analyses performed, various portions that have been selected for a VPU by extraction might be identified as unsuitable. Conversely, the analysis may reveal that certain portions that have been extracted for a PROCESSOR would be suitable for execution on a VPU.
An optional loop which leads back to the extraction portion after analysis based on suitable decision criteria to execute this loop with extraction specifications according to the analysis permits optimization of the translation results. This is thus an iteration. This procedure is preferred.
A loop may be introduced into the compiler run at various points.
The resulting NML code is to be partitioned according to the properties of the VPU used as needed, i.e., broken down into individual portions which may be mapped into the particular resources available.
A plurality of such mechanisms, in particular those based on graphic analysis, are known per se according to the related art. However, a preferred variant is based on analysis of the program sources and is known by the term temporal partitioning. This method is described in the aforementioned Ph.D. thesis by Cardoso, which is herewith incorporated to the full extent for disclosure purposes.
Partitioning methods, regardless of the type, are to be adapted according to the type of VPU used. When using VPUs which allow storage of intermediate results in registers and/or memories, the tie-in of the memories for storage of data and/or states is to be taken into account through the partitioning. The partitioning algorithms (e.g., the temporal partitioning) are to be adapted accordingly. Usually the actual partitioning and scheduling are greatly simplified and made possible in a reasonable manner for the first time through these patents.
Many VPUs offer the possibility of differential reconfiguration. This may be used when only relatively few changes within the configuration of PAEs are necessary in a reconfiguration. In other words, only the changes in a configuration in comparison with the present configuration are reconfigured. The partitioning in this case may be done so that the possibly differential configuration following a configuration contains only the required configuration data and does not constitute a complete configuration. It is possible to also take into account the configuration data overhead for analytical purposes in evaluating the partitioning efficiency.
The scheduling mechanisms for the partitioned codes may be expanded so that scheduling is controlled by acknowledgment messages of the VPU to the particular unit being reconfigured (CT and/or HOSTRECONF). In particular, the resulting possibility of a conditional execution, i.e., explicit determination of the subsequent partition by the state of the instantaneous partition, is utilized in partitioning. In other words, it is possible to optimize the partitioning so that conditional executions such as IF, CASE, etc. are taken into account.
If VPUs which have the ability to transmit status signals between PAEs are used, the PAEs responding to the particular states transmitted and/or cooperating in their processing, then within the partitioning and the scheduling, the additional execution may also be taken into account within the configuration of PAEs, i.e., without the necessity of complete or partial reconfiguration due to an altered conditional program run.
In addition, scheduling may support the possibility of preloading configurations during the run time of another configuration. A plurality of configurations may also be preloaded speculatively, i.e., without being certain that the configurations are needed at all. Through selection mechanisms, the configurations that are used may then be selected at run time (see also the example NLS in DE 10050442.6, EP 01 102674.7).
According to an additional or alternative variant, data processing within the VPU connected to the CPU requires exactly the same number of cycles as data processing within the computation pipeline of the CPU. In the case of today's high-performance CPUs having a plurality of pipeline stages (>20) in particular, this concept may be used ideally. The special advantage is that no separate synchronization measures such as RDY/ACK are necessary and/or no adaptation of opcodes to the register control is necessary. In this method, the compiler must ensure that the VPU maintains the required number of cycles and that data processing may be balanced by the insertion of delay stages such as a fall-through FIFO, such as that described in other patent applications cited above.
The code that is output is usually completely processable on the particular downstream compilers, preferably without any additional measures. If necessary, compiler flags and constraints may be generated for controlling downstream compilers, in which case the user may optionally add his or her own specifications and/or may modify the specifications generated. The downstream compilers do not require any significant modifications, so that standard conventional tools may in principle be used.
The method proposed here is thus suitable in particular as a preprocessor and/or as a processor method, for example, upstream from compilers and development systems. However, it should be pointed out explicitly that instead of and/or together with the translator described previously, compilers according to PACT11 (DE 101 39 1706; US 200310056202) may also be involved in principle.
An FPGA may be connected to the architecture described here, in particular directly to the VPU, to permit fine-grained data processing and/or to permit a flexibly adaptable interface (e.g., various serial interfaces (V24, USB, etc.), various parallel interfaces, hard drive interfaces, Ethernet, telecommunications interfaces (a/b, TO, ISDN, DSL, etc.)) to additional modules. The FPGA may be configured from the VPU architecture, in particular by the CT and/or by the CPU. The FPGA may be operated statically, i.e., without run time reconfiguration, and/or dynamically, i.e., with run time reconfiguration. Providing an interface code has already been mentioned. The interface code which is inserted into the extracted code may be predefined by various methods. The interface code is preferably stored in a database which is accessed. The unit for implementation may be designed to take into account a selection, e.g., by the programmer, in which the appropriate interface code is selected, e.g., based on instructions in the PROGRAM or by compiler flags. An interface code suitable for the implementation method of the VPU/CPU system, used in each case, may be selected.
connection methods between the VPU and CPU(s). This may be taken into account in the organization of the database by keeping an appropriate memory device ready and available for this information.
b) The interface code may be written by the user himself, who determined the system structure, or it may be modified from existing (exemplary) interface code and added to the database. The database is preferably designed to be user-modifiable in this regard to allow the user to modify the database.
c) The interface code may be generated automatically by a development system using which the system structure of the VPU-CPU system has been planned and/or described and/or tested, for example.
The interface code is usually preferably designed in such a way that it conforms to the requirements of the programming language in which the extracted code was written and into which the interface code is to be inserted.
Communication routines may be introduced into the interface codes to synchronize various development systems for the PROCESSOR and the VPU. In particular, code for the particular debugger (e.g., according to PACTI!) may also be included.
The interface code is designed to control and/or enable data exchange between the PROCESSOR and the VPU. It is therefore a suitable and preferred interface for controlling the particular development systems and debuggers. For example, it is possible to activate a debugger for the PROCESSOR as long as the data is being processed by the processor. As soon as the data is transferred via the interface code to one or more VPUs, a debugger for the VPUs is to be activated. If the code is sent back to the PROCESSOR, the PROCESSOR debugger is again to be activated. It is therefore also possible and preferable to handle such sequences by inserting control codes for debuggers and/or development systems into the interface code.
Communication and control between the different development systems should therefore preferably be handled via control codes introduced into the interface codes of the PROCESSOR and/or VPU. The control codes may largely correspond to existing standards for the control of development systems.
Administration and communication of the development systems are preferably handled as described in the interface codes, but they may also be handled separately from them (if appropriate) according to a corresponding similar method.
In many programming languages, in particular in sequential languages such as C, a precise chronological order is predetermined implicitly by the language. In the case of sequential programming languages, this is accomplished by the sequence of individual instructions, for example. If required by the programming language and/or the algorithm, the time information may be mapped onto synchronization models such as RDY/ACK and/or REQ/ACK or to a time stamp method.
The property of sequential languages of being controlled only by instruction processing is connected to the data flow principle of controlling processing through the data flow, i.e., the existence of data. In other words, an instruction and/or a statement (e.g., s:=s+inputstream;) is processed only when it is possible to execute the operation and the data is available.
It is noteworthy that this method does not usually result in any change in the syntax or semantics of a high-level language. More complex functions of a high-level language such as looping are implemented by macros. The macros are predefined by the compiler and are instantiated at the translation time.
Macros are constructed either of simple language constructs of the high-level language or they are constructed at the assembler level. Macros may be parameterized to permit simple adaptation to the algorithm described (see also PACT11).
A standard processor, e.g., an RISC, CISC or DSP (CPU), is thus linked to a reconfigurable processor (VPU).
Two different linkage variants, but preferably variants that may also be implemented simultaneously, may be described as follows.
A first variant includes a direct link to the instruction set of a CPU (instruction set linkage).
A second variant involves linkage via tables in the main memory. Tabulation means are therefore provided in this variant.
Free unused instructions are usually present within an instruction set (ISA) of a CPU. One or more of these free unused instructions is now used to control VPUs (VPUCODE).
A configuration unit (CT) of a VPU is triggered by the decoding of a VPUCODE, and executes certain sequences as a function of the VPUCODE. There is thus a responsive CT for VPU decoding.
A VPUCODE may, for example, trigger the loading and/or execution of configurations by the configuration unit (CT) for a VPU.
In an expanded embodiment, a VPUCODE may be translated to different VPU instructions via a translation table which is preferably managed by the CPU, or alternatively it may also be managed by the CPU, by a VPU, or from an external unit.
The configuration table may be set as a function of the CPU program or code section that has been executed.
After arrival of a load instruction, the VPU loads configurations out of its own memory or a memory shared with the CPU. In particular, a VPU configuration may be included in the code of the CPU program being executed at the moment.
After receiving an execution instruction, a VPU executes the configuration to be executed and performs the corresponding data processing. The end of data processing may be indicated to the CPU by a termination signal (TERM). Appropriate signal lines/interrupt inputs, etc. are present and/or configured accordingly.
Due to the occurrence of a VPUCODE, wait cycles may be executed on the CPU until the termination signal (TERM) of the termination of data processing by the CPU arrives.
In a preferred embodiment, processing of the next code continues. If another VPUCODE occurs, then it is possible to wait for the preceding code to be terminated or all the VPCODEs that have been started are queued in a processing pipeline or a task switch is performed, in particular as described below.
Termination of data processing is signaled by the arrival of the termination signal (TERM) in a status register. Termination signals arrive in the order of a possible processing pipeline.
Data processing on the CPU may be synchronized to the arrival of a termination signal by testing the status register.
In one possible embodiment, a task switch may be triggered if an application cannot be continued before the arrival of TERM, e.g., due to data dependencies.
It is preferable if loose links are established between processors and VPUs, in which VPUs function largely as independent coprocessors.
Such a linkage involves one or more shared data sources and data sinks, usually over shared bus systems and/or shared memories. Data is exchanged between a CPU and a VPU via DMAs and/or other memory access controllers. Data processing is preferably synchronized via an interrupt control or a status query mechanism (e.g., polling).
A tight linkage corresponds to the direct linkage of a VPU to the instruction set of a CPU, as described above.
In a direct arithmetic unit linkage, a high reconfiguration performance in particular is important. Therefore, wave reconfiguration is preferred. In addition, the configuration words are preferably preloaded so that when the instruction is executed, the configuration may be configured particularly rapidly (via wave reconfiguration, in the optimum case within one cycle). It would also be possible to provide a plurality of arrays, identical arrays in particular, instead of a partial array configuration in the case of high-performance applications, but also in the case of primarily low-performance applications in particular, and to reconfigure at least one of these for a new task, in particular in advance, and then to change easily and completely to another array as needed instead of a reconfiguration or partial reconfiguration of an integral multidimensional coarse-grained field which is partially reconfigurable in run time. Signals may be sent to the subarrays, e.g., via MUX1DEMUX stages, in particular I/O signals, data signals, status signals, and/or trigger signals.
For wave reconfiguration, the configurations that are presumably to be executed will preferably be recognized in advance by the compiler at compilation time and preloaded accordingly at run time.
At the time of instruction execution, the corresponding configuration is optionally selected and executed individually for each PAE and/or for a P AE subset. Such methods are also described in the publications identified above.
A preferred implementation may provide for different data transfers between a CPU and a VPU. Three particularly preferred methods that may be used individually or in combination are described below.
In the case of register linkage, the VPU may take data from a CPU register, process it and write it back to a CPU register.
Synchronization mechanisms are preferably used between the CPU and the VPU.
For example, the VPU may receive a RDY signal due to the data being written to the CPU register by the CPU and then the VPU may process the data thus written. Readout of data from a CPU register by the CPU may result in an ACK signal, which thus signals to the VPU data acceptance by the CPU. Use of the conventional RDY/ACK protocol in a different manifestation is advantageous in the present case precisely with coarse-grained cells of reconfigurable units.
CPUs do not typically make similar mechanisms available.
Two possible implementations are described in greater detail.
One approach that is easily implemented is to perform the data synchronization via a status register. For example, the VPU may indicate to the status register the successful readout of data from a register and the associated ACK signal and/or input of data into a register and the associated RDY signal. The CPU first tests the status register and performs wait loops or task switching, for example, until the RDY or ACK is received, depending on the operation. The CPU will then continue to perform the particular register data transfer.
In an expanded embodiment, the instruction set of the CPU is expanded by adding load/store instructions with an integrated status query (load_rdy, store_ack). For example, a new data word is written into a CPU register only when the register has first been read out by the VPU and an ACK signal has been received. Accordingly, load_rdy reads data out of a CPU register only when the VPU has previously entered new data and generated a RDY signal.
Data belonging to a configuration to be executed may be written to the CPU registers and/or may be read out of the registers successively more or less by block moves as in the related art. Block move instructions that are implemented if necessary may preferably be expanded by the integrated RDY/ACK status query described here.
A plurality of modifications and different embodiments of this basic method are possible.
The wave reconfiguration mentioned above allows starting of a new VPU instruction and the corresponding configuration as soon as the operand of the previous VPU instruction has been accepted from the CPU registers. The operands for the new instruction may be written directly into the CPU register after the instruction start.
According to the wave reconfiguration method, the VPU is reconfigured successively for the new VPU instruction on completion of data processing of the previous VPU instruction, and the new operands are processed.
In addition, data may be exchanged between a VPU and a CPU through suitable bus accesses to shared resources.
If there is to be an exchange of data that has been processed by the CPU just prior to the exchange and therefore is presumably still in the cache of the CPU which is preferably to be provided or if the data is processed by the CPU immediately next and therefore is logically placed in the cache of the CPU, this data is preferably read by the VPU out of the cache of the CPU or it is written to the cache of the CPU. This may be determined largely in advance at the compilation time through suitable analyses of the application by the compiler and the binary code may be generated accordingly.
If there is to be an exchange of data that is presumably not in the cache of the CPU and/or is presumably not needed subsequently in the cache of the CPU, it is preferably read directly by the VPU from the external bus and the data source connected to it (e.g., memory, peripheral) and/or written to the external bus and the data sink associated with it (e.g., memory, peripheral). This may be ascertained by the compiler largely in advance at compilation time of the application through suitable analyses, and the binary code may be generated accordingly.
In a transfer over the bus bypassing the cache, a protocol between the cache and the bus is preferably implemented, ensuring correct contents of the cache. For example, the conventional MESI protocol may be used for this purpose.
The methods described here need not at first have any particular mechanism for operating system support. It is preferable to ensure that an operating system to be executed behaves according to the status of a VPU to be supported, which is possible and to which end in particular schedulers may be provided.
In the case of a tight arithmetic unit linkage, the status register of the CPU into which the linked VPU enters its data processing status (termination signal) is preferably queried. If further data processing is to be transmitted to the VPU and the VPU has not yet terminated the previous data processing, the system will wait and/or a task switch will preferably be performed.
For coprocessor coupling, mechanisms controlled via the operating system, in particular the scheduler, are preferably used.
A simple scheduler may either allow the current task to continue running on the CPU after transfer of a function to a VPU, if it is able to run independently and simultaneously with data processing on a VPU. If or as soon as the task must wait for termination of data processing on the VPU, the task scheduler switches to another task.
Each task newly activated will check (if it uses the VPU) before use on whether the VPU is available for data processing and/or whether it is still processing data at the present time. Either it must then wait for termination of data processing or preferably the task is switched.
A simple and nevertheless efficient method may be created by so-called descriptor tables which may be implemented as follows, for example.
Each task generates one or more tables (VPUCALL) having a suitable fixed data format in the memory area assigned to it for callup of the VPU. This table contains all the control information for a VPU such as the program/configuration to be executed and/or the pointer to the memory location(s) or data sources of the input data and/or the memory location(s) or data sinks of the result data and/or additional execution parameters, e.g., data array variables.
The memory area of the operating system contains a table or an interlinked list (LINKLIST) which points to all the VPUCALL tables in the order of their creation.
Data processing on the VPU then takes place in such a way that a task creates a VPUCALL and calls up the VPU via the operating system. The operating system creates an entry in the LINKLIST. The VPU processes the LINKLIST and executes the particular VPU call referenced. The termination of the particular data processing is indicated by a corresponding entry in the LINKLIST and/or VPUCALL table.
The VPU thus works largely independently of the CPU. The operating system and/or the particular task must only monitor the tables (LINKLIST and/or VPUCALL).
These two methods are particularly efficient in performance if the VPU used has an architecture which allows reconfiguration that is and/or may be superimposed on data processing.
It is thus possible to start a new data processing and possibly a reconfiguration associated with it, immediately after reading the last operands out of the data sources. In other words, it is no longer the termination of data processing, but instead reading the last operands is necessary for synchronization. This greatly increases the performance in data processing.
The possible use of an operating system has an additional influence on the handling of states. Operating systems use task schedulers, for example, for managing multiple tasks to permit multitasking.
Task schedulers interrupt tasks at a certain point in time, start other tasks and, after the latter have been processed, resume processing of the interrupted task. Locally relevant states may remain unsaved if it is ensured that a configuration (which corresponds to processing of a task) will be terminated only after complete processing—i.e., when all data and states to be processed within this configuration cycle have been saved.
However, if the task scheduler interrupts configurations before they have been completely processed, local states and/or data must be stored. In addition, this is advantageous when the processing time of a configuration cannot be predicted. In conjunction with the known holding problem and the risk that a configuration will not be terminated at all (e.g., due to an error), this also seems appropriate to prevent a deadlock of the entire system.
In other words, taking into account task switching, relevant states may also be regarded as states which are necessary for task switching and correct restart of data processing.
Thus, in task switching the memory for results and, if necessary, also the memory for the operands must be saved and restored again at a later point in time, i.e., on returning to this task. This may be performed by a method comparable to the conventional PUSHIPOP instructions and methods. In addition, the state of data processing, i.e., the pointer to the last operand processed completely, must be saved. Reference should be made here in particular to PACT18.
a) The interrupted configuration is reconfigured and only the operands are loaded. Data processing begins anew as if the processing of the configuration had not even been started. In other words, all data computations are executed from the beginning, and if necessary, computations are even performed in advance. This option is simple but not very efficient.
b) The interrupted configuration is reconfigured, the operands and results that have already been calculated being loaded into the particular memory. Data processing is continued with the operands that have not been completely computed. This method is much more efficient, but it presupposes that additional states which occur during processing of the configuration may become relevant, if necessary; for example, at least one pointer to the last operand completely computed must be saved, so that it is possible to begin again with their successors after reconfiguration.
A particularly preferred variant for managing relevant data is made available through the context switching described below. In task switching and/or in executing and switching configurations (see, for example, patent application PACT15 (PCT/EP02/02398), which is herewith fully included for disclosure purposes) it may be necessary to save data or states, which are not typically saved together with the working data in the memories for a following configuration because they merely mark an end value, for example.
Context switching according to the present invention is implemented by removing a first configuration while the data to be saved remains in the corresponding memories (REGs) (memories, registers, counters, etc.).
A second configuration is loaded, connecting the REG in a suitable manner and in a defined 20 order to one or more global memories.
The configuration may use address generators, for example, to access the global memory (memories). The configuration may use address generators, for example, to access REGs designed as memories. According to the configured connection between the REGs, the contents of the REGs are written into the global memory in a defined order, with the particular addresses being specified by address generators. The address generator generates the addresses for the global memory (memories) so that the memory areas containing data (PUSH AREA) of the first configuration that has been removed may be assigned unambiguously.
In other words, different address spaces are preferably provided for different configurations. 30 This configuration corresponds to a PUSH of conventional processors.
Other configurations then use the resources.
The first configuration should be restarted. Before that, a third configuration interconnecting the REGs of the first configuration in a defined order is started.
The configuration may use address generators, for example, to access REGs configured as memories.
An address generator generates addresses so that correct access to the PUSH AREA assigned to the first configuration is achieved. The generated addresses and the configured order of the REGs are such that the data of the REGs is output from the memories and into the REGs in the original order. The configuration corresponds to that of a POP of conventional processors.
In summary, a context switch is performed so that by loading particular configurations which operate like PUSH/POP of conventional processor architectures, the data to be saved is exchanged with a global memory.
The function is to be illustrated in an example. A function adds up two rows of numbers, where the length of the rows is not known at translation time, but instead is known only at run time.
This function is now interrupted during execution, e.g., by a task switch, or because the memory provided for x is full. At this point in time, a, b and x are in memories according to the present invention; i and optionally length must be saved, however.
To do so, the configuration “example” is terminated, with the register content being saved and a configuration push being started, reading i and length out of the registers and writing them into a memory.
According to this embodiment, push is terminated and the register content may be deleted.
Other configurations are executed. After a period of time, the example configuration is restarted.
Before that, a configuration pop is started, and it reads the register contents out of the memory again.
After execution, pop is terminated and the register contents remain unchanged. The configuration “example” is restarted.
FIG. 1 shows an example of a possible system structure.
FIG. 2 shows an example compilation sequence.
FIG. 3 shows the structure of an example VPU.
FIG. 4 shows an example CPU.
FIG. 5 shows an example abstract system definition.
FIG. 6 shows an example interface.
FIG. 7 shows data transfers between VPU and CPU.
FIG. 8 shows a memory area of the operating system.
FIG. 1 illustrates an example of, in accordance with the present invention, an example method and shows a possible system structure, a PROCESSOR (0101) being connected to a VPU (0103) via a suitable interface (0102) for data exchange and status exchange.
A PROGRAM code (0110) is broken down (e.g., by a preprocessor for a compiler) into a portion (0111) suitable for the PROCESSOR and a VPU-suitable portion (0112), for example, according to the extraction methods described here.
Portion 0111 is translated by a standard compiler (0113) corresponding to the PROGRAM code, the additional code from a database (0114) for description and management of the interface (0102) between the PROCESSOR and a VPU being previously inserted. Sequential code executable on 0101 is generated (0116) and the corresponding programming (0117) of the interface (0102) is generated if necessary. The standard compiler may be of a type that is available as a conventional commercially available tool or as a portion of a development environment that is commercially available. The preprocessor and/or possibly the VPU compiler and/or possibly the debugger and additional tools may be integrated into an existing commercially available development environment, for example.
Portion 0112 is translated by a VPU compiler (0115), additional code for description and management of the interface (0102) being inserted from a database (0114). Configurations executable on 0103 are generated (0118) and, if necessary, the corresponding programming (0119) of the interface (0102) is also generated. It should be pointed out explicitly that in principle, compilers as described in DE 101 39 170.6 may also be used for 0115.
FIG. 2 shows a basic compilation sequence as an example. In the extraction unit (0202), a PROGRAM (0201) is broken down into VPU code (0203) and PROCESSOR code (0204) according to different methods. Different methods may be used in any combination for extraction, e.g., instructions in the original PROGRAM (0205) and/or subprogram calls (0206) and/or analytical methods (0207) and/or utilization of object-oriented class libraries (0206 a). The code extracted is translated, if necessary, and checked for its suitability for the particular target system (0208), if necessary. Feedback (0209) to the extraction is possible to obtain improvements due to modified allocation of the codes to a PROCESSOR or a VPU and/or a plurality of same.
Thereafter (0211) VPU code 0203 is expanded (0212) using the interface code from a database (0210) and/or (0204) is expanded using the interface code from 0210 to 0213.
The resulting code is analyzed for its performance (0214) and, if necessary, feedback (0215) to the extraction is possible to obtain improvements due to modified allocation of the codes to the PROCESSOR or a VPU.
The resulting VPU code (0216) is forwarded for further translation to a downstream compiler suitable for the VPU. For further translation, the resulting PROCESSOR code (0217) is processed further in any downstream compiler suitable for the PROCESSOR.
It should be pointed out that individual steps may be omitted, depending on the method. Generally, however, at least largely complete code, which is directly translatable without significant intervention by the programmer, or at least without any significant intervention, is output to the particular downstream compiler systems.
It is thus proposed that a preprocessor means be provided with a code input for supplying code to be compiled, with code analyzing means, in particular code structure and/or data format and/or data stream recognition and/or evaluation units, and with a segmenting evaluation unit for evaluating a code segmentation performed in response to signals from the code analyzing unit and, if necessary, with an iteration means for repeating a code segmentation until stable and/or sufficiently acceptable values are achieved, and with at least two partial code outputs, a first partial code output outputting partial code for at least one conventional processor, and at least one additional partial code output outputting code intended for processing by means of reconfigurable logic units, in particular multidimensional units having cell structures, in particular register means which process coarse-grained data and/or logic cells (PAEs) having arithmetic units and the like plus allocated register units, if necessary, and/or a fine-grained control means and/or monitoring means, such as state machines, RDY/ACK trigger lines and communication lines, etc.
Both partial code outputs may be located at one physical output as serial multiplex outputs.
The database for the interface codes (0210) is constructed independently of and prior to the compiler run. For example, the following sources for the database are possible: predefined by the supplier (0220), programmed by the user (0221) or generated automatically by a development system (0222).
FIG. 3 shows the structure of a particularly preferred VPU. Preferably hierarchical configuration managers (CTs) (0301) control and manage a system of reconfigurable elements (PACs) (0302). The CTs are assigned a local memory for the configurations (0303). The memory also has an interface (0304) to a global memory which makes the configuration data available. The configuration runs in a controllable manner via an interface (0305). An interface of the reconfigurable elements (0302) to sequence control and event management (0306) is present, as is an interface to the data exchange (0307). An interface of the reconfigurable elements (0302) for sequence control and event management (0306) is present as is an interface for data exchange (0307).
FIG. 4 shows details of an exemplary CPU system, e.g., a DSP of the C6000 type (0401) by Texas Instruments. This shows the program memory (0402), data memory (0403), any peripheral device (0404) and EMIF (0405). A VPU is integrated (0408) as a coprocessor via a memory bus (0406) and a peripheral bus (0407). A DMA controller (EDMA) (0409) may perform any DMA transfers, e.g., between the memory (0403) and the VPU (0408) or the memory (0403) and the peripheral device (0404).
FIG. 5 shows a more abstract system definition. A CPU (0501) is assigned a memory (0502) to which it has reading access and/or writing access. A VPU (0503) is connected to the memory. The VPU is subdivided into a CT portion (0509) and the reconfigurable elements for data processing (0510).
To increase the memory accesses, the memory may have a plurality of independent access buses (multiport). In a particularly preferred embodiment, the memory is segmented into a plurality of independent segments (memory banks), each bank being independently accessible. All the segments are preferably located within a uniform address space. One segment is preferably available mainly for the CPU (0504) and another segment is mainly available for data processing by the VPU (0505) while yet another segment is mainly available for the configuration data of the VPU (0506).
Typically and preferably, a fully configured VPU will have its own address generators and/or DMAs to perform data transfers. Alternatively and/or additionally, it is possible for a DMA (0507) to be provided within the system (FIG. 5) for data transfers with the VPU.
The system includes IO (0508) which may be accessible by the CPU and VPU.
The CPU and VPU may each have dedicated memory areas and IO areas to which the other has no access.
1 Basic addressees) of the CT memory area in 0506 for localizing the configurations.
2 Basic addressees) of data transfers with 0505.
3 IO addressees) of data transfers with 0508.
4 Synchronization information, e.g., resetting, stopping, starting the VPU.
5 Status information on the VPU, e.g., errors or states of data processing.
The CPU and the VPU are synchronized by data polling and/or preferably by interrupt control (0512).
FIG. 6 shows one possible embodiment of the interface structure of a VPU for tying into a system similar to that shown in FIG. 5. To do so, a memory/DMA interface and/or an IO interface is assigned (0601) to the VPU for data transfer; another system interface (0602) is responsible for sequence control such as managing interrupts, starting and stopping the processing, exchange of error states, etc.
The memory/DMA interface and/or IO interface is connected to a memory bus and/or an IO bus.
The system interface is preferably connected to an IO bus, but alternatively or additionally, it may also be connected to a memory according to 0511.
The interfaces (0601, 0402) may be designed for adaptation of different working frequencies of the CPU and/or the VPU and/or the system; for example, the system and/or the CPU may currently operate at 500 MHz and the VPU at 200 MHz.
The interfaces may perform a translation of the bus protocols, e.g., the VPU-internal protocol may be converted to an external AMBA bus protocol. They thus trigger bus protocol translation means and/or are designed for bus protocol translation, in particular bus protocol translation between an internal VPU protocol and a known bus protocol. It is also possible to provide for conversion directly to CPU-internal bus protocols.
The memory/DMA interface and/or the IO interface supports memory access by the CT to an external memory, which is preferably performed directly (memory mapped). The data transfer of the CT(s) and/or PAC(s) may be buffered, e.g., via FIFO stages.
External memories may be addressed directly; in addition, DMA-internal and/or external DMA transfers are also performed.
Data processing, e.g., the initialization, i.e., the start of configurations, is controlled via the system interface. In addition, status and/or error states are exchanged. Interrupts for the control and synchronization between the CTs and a CPU may be supported.
converted to external (standard) protocols (e.g., AMBA).
A preferred method of code generation for the system described here is described herein. This method describes a compiler which breaks down program code into code for a CPU and code for a VPU. The breakdown is performed by different methods on different processors. In a particularly preferred embodiment, the particular codes broken down are expanded by adding the interface routines for communication between CPU and VPU. The expansion may be performed automatically by the compiler.
0602), CTs and the PAC. The individual cycles are entered into the cells in the order of their execution. K1 references a configuration 1 that is to be executed.
It should be pointed out that synchronization between the EDMA and the VPU is performed automatically via interface 0401, i.e., DMA transfers take place only when the VPU is ready.
A second table shows a preferred optimized sequence as an example. The VPU itself has direct access to the configuration memory (0306). In addition, data transfers are executed by DMA circuit within the VPU, which may be fixedly implemented, for example, and/or formed by the configuration of configurable parts of the PAC.
The complexity for the CPU is minimal.
In summary, the present invention relates to methods that permit translation of a traditional high-level language such as Pascal, C, C++, Java, etc., onto a reconfigurable architecture. This method is designed so that only those portions of the program that are to be translated and are suitable for the reconfigurable target architecture are extracted. The remaining portions of the program are translated onto a conventional processor architecture.
For reasons of simplicity, FIG. 7 shows only the relevant components (in particular the CPU), although a significant number of other components and networks would typically be present.
A preferred implementation such as that in FIG. 7 may provide different data transfers between a CPU (0701) and a VPU (0702). The configurations to be executed on the VPU are selected by the instruction decoder (0705) of the CPU, which recognizes certain instructions intended for the VPU and triggers the CT (0706), so that it loads the corresponding configurations out of a memory (0707) assigned to the CT—which may be shared with the CPU in particular or may be the same as the working memory of the CPU—into the array of PAEs (PA, 0108).
CPU registers (0703) are provided to obtain data in a register connection, to process the data and to ‘write it back to a CPU register. A status register (0704) is provided for data synchronization. In addition, a cache is also provided, so that when data that has just been processed by the CPU is to be exchanged, it is still presumably in the cache (0709) of the CPU and/or will be processed immediately thereafter by the CPU.
The external bus is labeled as (0710) and through it, data is read out of a data source (e.g., memory, peripheral device) connected to it, for example, and/or is written to the external bus and the data sink connected to it (e.g., memory, peripheral device). This bus may in particular be the same as the external bus of the CPU (0712 & dashed line).
interlinked list (LINKLIST, 0801) which points to all VPUCALL tables (0802) in the order in which they are created.
reconfiguring itself into respective ones of the configurations that are defined by the loaded configuration definitions.
2. The method according to claim 1, wherein the conventional processor and the array processor are connected via both a shared memory and a bus system.
3. The method according to claim 2, wherein the conventional processor and the array processor share a cache.
4. The method according to claim 3, wherein a cache coherence protocol is implemented.
5. The method according to claim 3, wherein the cache comprises a plurality of segments, each being independently accessible.
6. The method according to claim 5, wherein the plurality of segments are within a unified address space.
7. The method according to claim 1, wherein the conventional processor and the array processor share a cache.
8. The method according to claim 7, wherein a cache coherence protocol is implemented.
9. The method according to claim 7, wherein the cache comprises a plurality of segments each being independently accessible.
10. The method according to claim 9, wherein the plurality of segments are within a unified address space.
11. The method according to claim 1, wherein the array processor is controlled by configurations provided in at least one list.
12. The method according to claim 11, wherein the at least one list is located in the shared memory.
13. The method according to claim 11, wherein the at least one list is a linked list.
14. The method according to claim 1, wherein a signal is generated by the array processor indicating a state of a current operation.
15. The method according to claim 14, wherein the signal schedules subsequent operations on the array processor.
16. The method according to claim 14, wherein the signal indicates that an operation has terminated.
US20030033514A1 (en) * 2000-07-20 2003-02-13 John Appleby-Allis System, method and article of manufacture for controlling peripherals and processing data on a system having no dedicated storage program and no central processing unit.
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