Patent Publication Number: US-6665855-B2

Title: Method and arrangement for rapid silicon prototyping

Description:
RELATED PATENT DOCUMENTS 
     This is a continuation of U.S. patent application Ser. No. 09/215,942, filed on Dec. 18, 1998, now U.S. Pat. No. 6,347,395, and bearing the same title; priority to which is claimed under 35 U.S.C. §120. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed generally to semiconductors and their design and development involving hardware simulation (or emulation). More particularly, the invention relates to hardware emulation methods and arrangements involving reconfigurable and reusable circuits in an IC reference platform for expediting the design time of customized chips. 
     BACKGROUND OF THE INVENTION 
     The electronics industry continues to strive for high-powered, high-functioning circuits. Significant achievements in this regard have been realized through the fabrication of very large-scale integration of circuits on small areas of silicon wafer. Integrated circuits of this type are developed through a series of steps carried out in a particular order. The main objective in designing such devices is to obtain a device that conforms to geographical features of a particular design for the device. To obtain this objective, steps in the designing process are closely controlled to insure that rigid requirements are realized. 
     Semiconductor devices are used in large numbers to construct most modem electronic devices. In order to increase the capability of such electronic devices, it is necessary to integrate even larger numbers of such devices into a single silicon wafer. As the semiconductor devices are scaled down (i.e., made smaller) to form a larger number of devices on a given surface area, the structure of the devices and the fabrication techniques used to make such devices have become more refined. This increased ability to refine such semiconductor devices has lead to an ever-increasing proliferation of customized chips, and with each chip serving a unique function and application. This, in turn, has lead to various techniques to design and successfully test chips efficiently and inexpensively. 
     For many chip designs, customized chips are made by describing their functionality using a hardware-description language (HDL), such as Verilog or VHDL. The hardware description is often written to characterize the design in terms of a set of functional macros. The design is computer simulated to ensure that the custom design criteria are satisfied. For highly-complex custom chip designs, the above process can be burdensome and costly. The highly integrated structure of such chips leads to unexpected problems, such as signal timing, noise-coupling and signal-level issues. Consequently, such complex custom chip designs involve extensive validation. This validation is generally performed at different stages using a Verilog or VHDL simulator. Once validated at this level, the Verilog or VHDL HDL code is synthesized, for example, using “Synopsys,” to a netlist that is supplied to an ASIC (Application Specific Integrated Circuit) foundry for prototype fabrication. The ASIC prototype is then tested in silicon. Even after such validation with the Verilog or VHDL simulator, unexpected problems are typical. Overcoming these problems involves more iterations of the above process, with testing and validation at both the simulation and prototype stages. Such repetition significantly increases the design time and cost to such a degree that this practice is often intolerable in today&#39;s time-sensitive market. 
     Accordingly, there is a need for a way to develop customized chips that overcomes the above-mentioned deficiencies. The present invention addresses this need, and other needs, by way of a rapid silicon prototyping (RSP) process and arrangement in which a typical development period (from initial design to new product) can be reduced by more than fifty percent. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a semiconductor device designed using a rapid silicon process and/or processing arrangement. According to the present invention, the design effort of such devices is significantly benefited in connection with the design validation phase of the overall device implementation. 
     According to one embodiment, a rapid silicon process and processing arrangement involves the design of a high-complexity custom chip using design re-use, and on-chip bus architectures in a way that improves the ability of designers to create advanced custom integrated circuits (ICs) faster and with higher probabilities of success. 
     Consistent with one embodiment, the present invention is directed to a method for designing a semiconductor circuit arrangement, including its validation. The method comprises: providing a deconfigurable and extendible reference-chip development platform that is programmable, and that includes a programmable circuit and a plurality of functional block macros; using a collection of functional block macros at least one of which is obtained from the deconfigurable and extendible reference-chip development platform; extending the deconfigurable and extendible reference-chip development platform, including communicatively coupling at least one external device with the reference-chip development platform, and thereby providing an extended reference-chip development platform that enables co-development and co-validation of hardware and software. A subset of the collection of functional block macros can then be processed, e.g. synthesized, to the programmable circuit, and then a hardware representation of the synthesized subset of functional block macros in the programmable circuit can be validated within the extended reference-chip development platform. 
     Consistent with another embodiment, the present invention is directed to a rapid silicon process involving the validation of a FPGA and its implementation to a finished ASIC. This method embodiment of the present invention comprises the above-characterized method and in addition using at least one of the functional block macros in the subset from a functional block macro obtained from the deconfigurable and extendible reference-chip development platform and reusing this same functional block macro(s) in the subset by retargeting to an ASIC that is developed from the hardware representation. 
     According to another embodiment, the present invention is directed to a system for designing a semiconductor circuit arrangement. The system comprises: a deconfigurable and extendible reference-chip development platform that is programmable, and includes a hardware reconfigurable circuit and a plurality of functional block macros; a collection of functional block macros at least one of which is obtained from the deconfigurable and extendible reference-chip development platform; an interface circuit configured and arranged to extend the deconfigurable and extendible reference-chip development platform, including a two-way buffer arrangement and logic circuitry adapted to communicatively couple a plurality of external devices with the reference-chip development platform, and thereby provide an extended reference-chip development platform that enables co-development and co-validation of hardware and software; a synthesizer adapted to cause the subset of the collection of functional block macros to be represented as a configuration of the hardware reconfigurable circuit; and wherein the extended reference-chip development platform is adapted to validate the configuration in the hardware reconfigurable circuit within the extended reference-chip development platform. 
     Another aspect of the present invention is directed to a system for designing a semiconductor circuit arrangement. The system comprises: a deconfigurable and extendible reference-chip development platform that is programmable, and includes a programmable circuit and a plurality of functional block macros; a collection of functional block macros at least one of which is obtained from the deconfigurable and extendible reference-chip development platform; an interface circuit configured and arranged to extend the deconfigurable and extendible reference-chip development platform, including a bus and logic circuitry adapted to communicatively couple at least one external device with the reference-chip development platform, and thereby provide an extended reference-chip development platform that enables co-development and co-validation of hardware and software; a synthesizer adapted to cause the subset of the collection of functional block macros to be represented as a configuration of the programmable circuit; and wherein the extended reference-chip development platform is adapted to validate the configuration in the programmable circuit within the extended reference-chip development platform. 
     Other aspects of the present invention are directed and related to apparatuses and methods of design validation, each using one or more of the above rapid silicon process features. 
    
    
     The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description that follow more particularly exemplify these embodiments. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
     FIGS. 1 a ,  1   b  and  1   c  illustrate how a chip development reference design (FIG. 1 a ) can be used to validate a functional macro described in HDL (FIG. 1 c ) and later re-targeted to a manufactured ASIC (FIG. 1 b ), in accordance with a rapid silicon prototyping embodiment that is consistent with the present invention; 
     FIG. 2 illustrates a rapid silicon prototyping arrangement, according to one aspect of the present invention; 
     FIG. 3 illustrates an example embodiment of an emulation board, according to another aspect of the present invention; 
     FIG. 4 illustrates an example embodiment of a two-way bus-buffer interface arrangement, according to another aspect of the present invention; and 
     FIGS. 5 a ,  5   b  and  5   c  illustrate an example embodiment of an emulation board, according to the present invention. 
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of examples in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS 
     The present invention is believed to be generally applicable to the design of custom semiconductor chip devices. The invention has been found to be particularly advantageous for validation applications involving the development of highly-complex custom semiconductor chips where efficiency in terms of cost and turn-around time are considered to be important. While the present invention is not so limited, an appreciation of various aspects of the invention is best gained through a discussion of examples in such an environment where a functional block is defined in a hardware description language and then synthesized into a programmable circuit. 
     Turning now to the drawings, FIGS. 1 a  and  1   b  illustrate a rapid silicon prototyping implementation, according to the present invention, at two different stages of development. FIG. 1 a  includes a reference-chip development platform  100  that employs a collection of functional block macros  104  to design a custom silicon chip. The reference-chip development platform  100  is used in connection with a method involving a number of steps, including the integration of selected ones of the functional block macros  104 , the deselection or deconfiguration of other ones of the functional block macros  104 , and the synthesis of HDL source code into a hardware (re-) configurable circuit  110 . 
     FIG. 1 b  depicts a derivative of the reference-chip development platform  100  in the form of a validated custom integrated circuit  102 . A functional prototype of the custom integrated circuit  102  is validated on the reference-chip development platform  100  before manufacturing device  102 , using various tools that can validate for, and/or be integrated with, the specified design criteria, such as a customer&#39;s requirements for a specific application, as characterized by the selected and deselected functional block macros  104 . 
     FIG. 1 c  depicts a functional macro  110  described in HDL code  108  that is targeted to the reference-chip development platform  100  by synthesizing it. Subsequently, the same HDL code  108  is synthesized for the final ASIC  102  without requiring modification. The functional macro  110  that is integrated into the final ASIC  102  has already been validated in the reference-chip development platform  100 . 
     A software program is developed to exercise the hardware in the reference-chip development platform  100 . This same program can be reused to exercise the custom integrated circuit  102 . 
     Consistent with these above-discussed features, the deconfigurability and extendibility aspects permit both for redaction of potential (but unneeded) functionality and for use of external devices in connection with the reference-chip development platform  100 . These aspects of the present invention offer significant advantages in connection with the emulation and debugging of the custom integrated circuits, such as the integrated circuit  102  shown in FIG. 1 b.    
     In this context, deconfigurability refers to the deselection of communicative activity by one or more programmable components, depicted as blocks  104  in FIG. 1 a . For example, the components  104  can be deselected by programming the reference-chip development platform  100  such that the blocks  104  are not addressed, thereby disabling communication by ignoring the blocks  104 . The components  104  can also be removed without impacting the programmed reference-chip development platform  100 . In alternative embodiments, the components  104  are deselected, respectively, by physically disabling communication to components  104 . Example methods of physically disabling communication include programming configuration registers, reassigning memory maps, or de-asserting external enable signals. In each of these alternative embodiments, the reference-chip development platform  100  can be programmed such that they attempt to address and communicate with the blocks  104  or programmed such that they do not attempt to address and communicate with the blocks  104 . 
     Extendibility is provided by the reference-chip development platform  100  permitting external devices to be coupled to the reference-chip development platform by way of an off-platform bus  106  that does not require use of a bus bridge and its associated clocking protocol. Thus, this extendibility permits for virtual transparency insofar as the external devices are able to communicate with the reference-chip development platform via the bus  106 , as though the external devices were physically on the integrated circuit (IC) and part of the reference-chip development platform. As further discussed below, this virtual transparency is implemented using a master/slave communication relationship involving a two-way signal buffer as an interface between the reference-chip development platform and the external devices. 
     According to one specific implementation, each or selected ones of the components  104  are repeatedly used for a multitude of chip design applications. 
     FIG. 2 illustrates other examples of how the deconfigurability and extendibility can be used, according to the present invention, to develop a custom IC, such as the IC  102  of FIG. 1 b . More specifically, FIG. 2 illustrates an example system including a reference-chip development platform  210 , constructed and arranged with the above-discussed features. 
     Further, FIG. 2 illustrates a hardware accelerator  220 , a standard plug-in board  222 , a logic analyzer  224 , a microprocessor-based host compiler and debugger  226  coupled to the reference-chip development platform  210  using a JTAG control module  228 , and a user interface  230 . In one example implementation, the hardware accelerator  220  is implemented using equipment commercially available from IKOS Systems, Inc. The microprocessor-based host compiler and debugger  226  is implemented, in various embodiments, using one of several different types of programmable processors, including but not limited to an ARM or a DSP (such as VLSI Technology&#39;s OAK or Palm type processors). 
     The standard plug-in board  222  is used to extend the system beyond the FPGA capability and to provide connectivity with the off-chip bus (e.g., bus  106  of FIG. 1 a ). Example types of plug-in boards that may be used in this regard include those available from Philips Semiconductors, Inc. (VLSI Technology, Inc.); users of the reference-chip development platform  210 , however, can implement any custom or conventional plug-on logic for communication with the reference design busses. 
     The logic analyzer  224  is used to monitor the progress of the logic states of the functional block under evaluation. Compatible logic analyzers are available from Hewlett Packard, Inc. In one implementation, the logic analyzer  224  is programmed with HP Logic Analyzer Configuration Files, which are available from Philips Semiconductors, Inc. of San Jose, Calif. 
     The microprocessor-based host compiler and debugger  226  is conventional (e.g., a VLSI Technology Jumpstart Tool) and is used to compile and debug software source code. The JTAG control module  228  can be implemented using any JTAG control device such as the Jeeni box available from Philips Semiconductors, Inc. 
     The user interface  230  is exemplified in FIG. 2 as a conventional cellular telephone, but can be any “box” (or product) that would be implemented by the result of the development/validation effort via the reference-chip development platform  210 . In a typical application, user interface  230  includes an output (such as an electronic display or scribed output) and an input (such as a keypad or switches) for inputting data to the reference-chip development platform  210 . In this manner, the reference-chip development platform  210  is used to test and validate the functionality of the design of the subject FPGA(s) while using actual input and generating actual output data representative of the system being implemented. 
     An on-board FPGA (field programmable gate array)  232  is used to integrate application and/or customer specific functional blocks onto the busses ( 106  of FIG. 1 a ). In connection with integrating such functional blocks onto the busses to implement a functional block macro, the FPGA  232  can be used, other devices such as the hardware accelerator  220  and the FPGA prototype arrangement  234 / 236  can be used, or two or more of these input configuration sources can be in combination. It will also be appreciated that the ASIC is merely one type of programmable circuit into which such functional block macros are synthesized. Other types of programmable circuits of the hardware-configurable types include, but are not limited to, programmable logic devices (PLDs) including PALs and PLAs, complex PLDs, FPGAs and microcontrollers. 
     FIG. 3 illustrates an example embodiment of how the FPGA  232  functionality is validated using the emulation board. Once the application or customer specific functional blocks are integrated onto the busses, functional blocks inside the FPGA  232  are accessible within the RSP IC  310  just as if these functional blocks were inside the RSP IC  310 . The on-chip and off-chip logic, relative to the RSP IC  310 , can then be operated as one cohesive system and hardware and software co-validation can commence. 
     The logic for integrating is downloaded into the FPGA  232  by first synthesizing a register-transfer-level (RTL) HDL description (for example, using Verilog or VHDL) and then routing the resulting netlist into the FPGA  232 . The developer then validates the function of that macro at or near real time speeds, usually by writing software to the target CPU (for example, the ARM CPU  324 ). Referring also to FIG. 2, logic analyzer(s)  224 , oscilloscopes (not shown), software debuggers  226  and  228  and other tools such as USB Traffic Generators can be used to analyze various signals or model system interfaces. Internal signals on the block-under-test can easily be inspected by simply routing those signals to pins on the FPGA  232  and viewing them with the logic analyzer  224 . 
     Once the system with the off-chip logic extensions is validated, the RSP IC  310  can be created. The same RTL description of the macro or macros, depicted as  108 , that were put into the FPGA  232  can be synthesized at this stage using the same synthesis tools as before. No RTL modifications need to be made to the RTL HDL between the FPGA and ASIC versions. In this regard, the RSP acts as a “silicon simulator,” permitting that which is validated in the RSP system to be built into the ASIC. The above-mentioned devices, that are external to the reference-chip development platform  210 , are bus-coupled to the reference-chip development platform  210  for the purpose of synthesizing the functionally-defined block(s) and developing a customized FPGA prototype board  236  of FIG. 2 or on board FPGA  232 . 
     Another important aspect of the present invention, and of the emulation board of FIG. 3, concerns the extendibility of the RSP IC  310  via the off-platform bus  106  (also in FIG. 1 a ) and an off-chip interface  320 . The interface  320  uses a general bus  322 , but can be implemented using any of a variety of interfaces, including but not limited to PCI (Peripheral Component Interconnect) and AMBA (Advanced Microcontroller Bus Architecture) ASB (Advanced System Bus) compliant interfaces. The example interface illustrated in FIG. 3 provides a two-way signaling interface between an ASB bus  322  and the off-platform bus  106 . This two-way signaling interface is provided in connection with the microprocessor, in this illustrated example an ARM CPU,  324  coupled to the bus  322 . The off-chip interface  320  is designed to provide virtual transparency between the external devices that are communicatively coupled via the off-platform bus  106  and the bus  322 , with an important advantage being that no bus-bridge interface and/or its associated clocking protocols are needed to pass data therebetween. Accordingly, using the off-platform bus  106  and the off-chip interface  320 , the RSP IC  310  forms part of an extended reference-chip development platform. 
     Where a typical bus interface would be a bus-bridge interface such as a PCI-bridge implementation, in accordance with the present invention, communication across the buffers in the off-chip interface  320  is implemented using a master/slave communication relationship. When any external device communicates using the bus  322 , the off-chip interface  320  includes logic configured to determine whether the external device is the master or the slave. In this context, the master is the device initiating the communication, and the slave is the targeted respondent of the initiated communication. Once this master/slave determination is made, the logic controls the two-way buffers such that: for information written from the master to the slave, the control, address and data signals are copied from the master side of the off-chip interface  320  to the slave side of the off-chip interface  320 ; and for information read by the master from the slave, the control, address and data signals are copied from the slave side of the off-chip interface  320  to the master side of the off-chip interface  320 . 
     A key advantage of this approach is that the programming for the CPU  324  does not depend on the location of the CPU, on-chip or off-chip, of functional macros resident on the busses. The logic in the interface  320  makes the communication virtually transparent. Consequently, with essentially only one CPU program to debug, the overall validation time is minimized. 
     The emulation board of FIG. 3 further includes a shared-address extension arrangement  328  that permits the CPU  324  to communicate with multiple units  335 - 340 . In the example arrangement of FIG. 3, the multiple memory units include ROM, Flash, SRAM and DRAM types memory devices; others, however, may be used as well. 
     Other aspects of the emulation board are conventional and include interfaces well known to those skilled in the art. To name a few of those illustrated, the RSP IC  310  includes a conventional JTAG test port  350  for a JTAG test interface  352 , an off-chip VLSI (Technology) Peripheral Bus (VPB) interface  354 , and an on-chip ASB2VPB bridge interface  358 . For further information concerning the interfaces  354  and  358  and VLSI Technology adaptations to the JTAG interface  350 , reference may be made to commercially available VLSI Technology specifications characterizing these interfaces. 
     Communicating over the on-chip ASB2VPB bridge interface  358  are various conventional interfaces and devices. As shown in FIG. 3, these interfaces and devices include a general purpose input/output interface  360  for interfacing with a (dot-matrix or segment-type) display and an input device, a battery-powered real-time clock (RTC) unit  362 , a universal serial bus (USB) interface  364 , an IrDA interface  366 , an I 2 C interface  368 , a UART device  370 , an interrupt controller  371 , and timers  372 . The skilled artisan will appreciate that various implementations of this emulation board can include additional or fewer interfaces and devices. Including such interfaces and devices may depend upon factors including, among others, available silicon and congestion on one or more of the busses. Various commercially-available devices, such as the equipment addressed in the discussion above, can be used to enhance the flexibility of the design development and validation. For access to example equipment and software-related packages that may be useful in connection to various embodiments discussed above, reference may be made to the RSP7 User Guide, available from Philips Semiconductors, Inc. (VLSI Technology, Inc.), attached to the above-referenced parent patent application. 
     FIG. 4 illustrates a more particular example embodiment of a two-way interface arrangement  410 , in accordance with the present invention, that can be used in connection with an implementation of the off-chip interface  320  of FIG.  3 . The two-way interface arrangement  410  includes a logic (or control) circuit  412 , and three sets of two-way buffers, a plurality of data bus buffers  414 , a plurality of SD (slave-driven) buffers  416 , and a plurality of MD (master-driven) buffers  418 . One approach for implementing the off-chip interface  320  of FIG. 3 has the left side of the two-way interface arrangement  410  connecting to the off-platform bus  106  and the other side connecting to the bus  322 . The logic (or control) circuit  412  responds to slave select status signals carried by lines  422  and to bus arbitration signals carried by lines  428 . When the bus  322  is implemented using the illustrated AMBA ASB bus, the slave select status signals and the bus arbitration signals are as defined by the AMBA ASB bus/interface and respectively driven by a central bus decoder, depicted as  323  in FIG. 3, and a central bus arbiter, depicted as  325  in FIG.  3 . 
     Consistent with the off-chip interface  320  of FIG. 3, the data bus buffer  414 , the SD buffer  416  and the MD buffer  418  and the control block  412  are configured as described previously so as to provide a master/slave bus-copying communication relationship. 
     According to one specific embodiment, the two-way interface arrangement  410  has four noteworthy operations. First, using the bus arbitration signals, the control block  412  determines the location of the current master. For an AMBA ASB bus (e.g., bus  322  of FIG.  3 ), determining the location of the current master also requires that the control block  412  monitor the AMBA-ASB-defined AGNT and BWAIT signals. Second, the control block  412  determines the location of the current slave by monitoring the slave select status signals and, for an AMBA ASB bus, this determination requires monitoring the DSEL signals. Third, the control block  412  determines the direction in which data is to be transferred and, for an AMBA ASB bus, this determination requires monitoring the AMBA-ASB-defined BWRITE signal. A “read” entails a data transfer from slave to master, and a “write” entails a data transfer from master to slave. The fourth operation is the control block  412  enabling or disabling the three-state buffers between the two interfacing busses to effect proper bi-directional data movement. 
     As shown in connection with FIGS. 5 a ,  5   b  and  5   c , the three two-way buffers of FIG. 4 are enabled and disabled according to a set of general rules, an example of which follows. 
     FIG. 5 a  depicts an example set of rules for the MD buffer  418  for master-driven control (including address) signals. At block  510  of FIG. 5 a , the control block  412  determines if an internal (relative to the IC) device currently has control over the bus, in which case the internal device is the master. The control block  412  responds to a determination that the internal device is the master by enabling the outbound buffers  418   a  of the MD buffer  418 , and the control signals (including the address signals) are thereby copied from the internal side to the external side of the interface. If the control block  412  determines that an internal device currently does not have control over the bus, flow proceeds from decision block  510  to decision block  520  where the control block  412  determines if an external device is the master. If an external device is the master, the control block  412  responds by enabling the inbound buffers  418   b  of the MD buffer  418 , and the control signals (including the address signals) are thereby copied from the external side to the internal side of the interface. If neither side has control over the bus, the control block  412  does not enable any of the buffers  418   a ,  418   b.    
     FIG. 5 b  depicts an example set of rules for the SD buffer  416  for slave-driven response signals. At block  530  of FIG. 5 b , the control block  412  determines if an internal (relative to the IC) device is currently selected as a slave. If so, the control block  412  responds by enabling the outbound buffers  416   a  of the SD buffer  416 , and the response signals are thereby copied from the internal side to the external side of the interface. If the control block  412  determines that an internal device is not a slave, flow proceeds from decision block  530  to decision block  540  where the control block  412  determines if an external device is selected as a slave. If an external device is selected as a slave, the control block  412  responds by enabling the inbound buffers  416   b  of the MD buffer  416 , and the response signals are thereby copied from the external side to the internal side of the interface. If neither side (internal or external) has a device selected as a slave, the control block  412  does not enable any of the buffers  416   a ,  416   b.    
     FIG. 5 c  depicts an example set of rules for the data bus buffer  414  for data transfer signals. At block  550  of FIG. 5 c , the control block  412  determines if data is being or read. If data is being written, the control block  412  proceeds to block  552  where it determines if an internal device is the master and, if so, the control block  412  enables the outbound buffers  414   a  of the data bus buffer  414 . If data is being read, the control block  412  proceeds from block  550  to block  558  where it determines if an internal device is selected as a slave and, if so, the control block  412  enables the outbound buffers  414   a  of the data bus buffer  414 . Accordingly, a positive outcome of a decision at either block  552  or block  558  results in data being copied from the internal side to the external side of the interface. 
     A negative outcome of a decision at either block  552  or block  558  results in the control block  412  proceeding either to block  562  or block  564 . At each of these blocks, the control block  412  determines if it should enable the inbound buffers  414   b  of the data bus buffer  414 . From block  562 , the inbound buffers  414   b  are enabled if an external master owns the bus, and, from block  564 , the inbound buffers  414   b  are enabled if an external slave owns the bus. Otherwise, from either block  562  or block  564 , the buffers  414   a  and  414   b  are not enabled. 
     When implementing the general bus  322  of FIG. 3 as an AMBA ASB bus, the above discussion is modified in that the control block  412  proceeds from block  540  by enabling the associated outbound buffers. This is because, for the AMBA ASB bus, the slave response signals are constantly being driven by some device. When no slave is selected, the ASB decoder (e.g.,  323  of FIG. 3) drives the response signals. 
     Decision-making transitions internal to the control block  412  flow from one flow segment to the next, for example, from FIG. 5 a  to FIG. 5 b  to FIG. 5 c . Once the illustrated flow of any of FIGS. 5 a ,  5   b  and  5   c  is complete, the control block  412  is adapted to continue monitoring the slave select and bus arbitration signals by picking up at the beginning of the next flow segment. 
     In accordance with other specific embodiments, the RSP7 User Guide, as attached hereto in the form of an appendix, may be referred to for additional information generally. This appendix is incorporated herein in its entirety. 
     For further information regarding the implementation of FIG. 4, reference may be made to U.S. patent application Ser. No. 09/216,291, also filed on Dec. 18, 1998, and entitled METHOD AND ARRANGEMENT FOR BUS EXTENSION WITH VIRTUAL TRANSPARENCY, incorporated herein by reference. 
     The present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable fall within the scope of the present invention. For example, the busses on either side of the two-way interface  320  of FIG. 3 do not necessarily have to be of the types discussed above. Further, the skilled artisan will appreciate that, while the programmable circuit  310  of FIG. 3 is readily designed from into a single chip, other multi-chip arrangements are also acceptable, and that such multi-chip arrangements can be implemented using a similarly constructed, or another variety of, two-way interface for communication between the chip arrangements. The claims are intended to cover such alternative approaches as well.