Abstract:
An improved FPGA comprising, a direct interconnect structure for providing selective data routing without stressing the general-purpose routing resources and enabling high rate of data exchange within the FPGA. At least two IP cores are connected to each other through said direct interconnect structure for enabling simultaneous data interaction among the ports of said IP cores and for providing configurable bus width routing between said IP cores, and a plurality of logic blocks connected to said IP cores through said direct interconnect structure for enabling simultaneous data routing among said IP cores and said plurality of logic blocks.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to general-purpose routing resources and in particular to an implementation of a direct routing structure between complex IP cores in FPGA.  
       BACKGROUND OF THE INVENTION  
       [0002]     FPGA architecture comprises a programmable routing structure and an array of configurable logic blocks. The programmable routing matrix comprising means for connecting configurable logic blocks (hereafter referred as logic blocks) to each other. An FPGA provides a combination of programmable logic and programmable connections to a general-purpose routing structure.  
         [0003]     In conventional FPGAs, the Programmable Interconnect Points (PIPs) are turned on by loading appropriate values into configuration memory cells associated with the PIPs, thereby creating paths for routing and establishing the logic performed by the configurable logic blocks. The signals on the routing paths change dynamically as values are being written to and read from flip-flops. A large amount of data is exchanged between logic blocks involving complex arithmetic and logic operations. The general-purpose routing resources are used to implement the interconnects between complex logic blocks. Data between the blocks is routed through the available switch matrix structure in the FPGA.  
         [0004]     An existing interface between complex logic blocks in FPGA is an interface between RAM and Digital Signal Processor (DSP) block. In conventional FPGAs the blocks of RAM are generated by configuring programmable parts of the FPGA. When the functionality of RAM is desired by multiple end users, it is economical to dedicate a portion of the chip to this purpose, thus allowing the particular function to be implemented at high density.  
         [0005]     Signal processing applications require execution of complex arithmetic and logical operations within the Configurable Logic Blocks. These blocks include MAC units, memory blocks, multipliers, shift registers, adders.  
         [0006]     U.S. Pat. No. 5,933,023 describing the existing structure of RAM blocks embedded in FPGAs, and is illustrated by  FIG. 1A . The patent describes a structure in which blocks of RAM are integrated with Configurable Logic Blocks in FPGA. Routing lines which access configurable logic blocks also access address, data, and control lines in the RAM blocks. The logic blocks of the FPGA can use these routing lines to access portions of RAM. The routing lines allow RAM blocks and arrays of RAM blocks to be configured long, wide, or in between, and allow logic blocks to conveniently access RAM blocks in a remote part of the chip.  
         [0007]     The drawback in the above said patent is that it cannot be used to provide an efficient routing structure between complex IP cores, where high rate of data exchange is required.  
         [0008]      FIG. 1B  is a block diagram of a configurable memory array device  200  in accordance with U.S. Pat. No. 6,104,208, which describes the function specific blocks in detail. The configurable memory array device  200  comprises configurable memory array blocks  202  ( 202 - 1  through  202 - 3 ) connected to a functional block  204  by way of a signal bus  206 . The signal bus  206  carries data and control signals, from the functional block  204  to the configurable memory array blocks ( 202 - 1  through  202 - 3 ) by using bi-directional signal lines  208 - 1  through  208 - 3 . The configurable memory array blocks  202 - 1  through  202 - 3  respectively connect to external circuitry by way of bi-directional input/output (I/O) lines;  210 - 1  through  210 - 3 .  
         [0009]     The connectivity between the DSP block and the RAM blocks in U.S. Pat. No. 6,104,208 is not efficient and the connections have to be made using general-purpose routing resources, and Reconfigurable Interconnects are used for the purpose of routing.  
         [0010]      FIG. 1C  shows the multifunction tile by Xilinx according to U.S. Pat. No. 6,573,749. The patent describes the method and apparatus of incorporating a multiplier into an FPGA. The invention provides an alternative structure that shares routing resources with a programmable structure having variable width. The document describes a multifunction tile and in one of the embodiments, the multifunction tile includes a configurable, dual-ported RAM and a multiplier that share the Input/Output resources of the multi-function tile. The RAM block and the multiplier block share their inputs bits and therefore, whenever the multiplier block is being used, the RAM block cannot be used in 32-bit mode.  
         [0011]     The connectivity of the multiplier block and RAM block in the above discussed patent is such that whenever the multiplier block is being used, the associated RAM block can only be used in specific modes (18 bit or lesser). The multiplier inputs and outputs cannot be stored in the associated RAM block.  
         [0012]     It is therefore felt that a direct interconnect structure is required between complex IP cores (Digital Signal Processors, Memory, High speed microprocessors) in FPGA, to avoid inefficient performance of general-purpose routing resources and for providing an integral connectivity between the complex IP cores and FPGA.  
       SUMMARY OF THE INVENTION  
       [0013]     To address the above-discussed deficiencies of the prior art, it is an object of the present invention to provide a direct interconnect structure between complex IP cores in FPGA.  
         [0014]     It is another object of the present invention to provide configurable bus width connectivity between the IP cores.  
         [0015]     It is further an object of the present invention to provide simultaneous routing of data among the IP cores and the logic blocks in FPGA.  
         [0016]     To achieve said objectives the present invention provides an improved FPGA having a direct routing structure, comprising:  
         [0017]     a direct interconnect structure for providing selective data routing without stressing the general-purpose routing resources and enabling high rate of data exchange within the FPGA,  
         [0018]     at least two IP cores connected to each other through said direct interconnect structure for enabling simultaneous data interaction among the ports of said IP cores, and providing configurable bus width routing between said IP cores, and  
         [0019]     a plurality of logic blocks connected to said IP cores through said direct interconnect structure for enabling simultaneous data routing among said IP cores and said plurality of logic blocks.  
         [0020]     Further, the present invention provides a method for implementing direct routing in FPGA, the method comprising steps of:  
         [0021]     enabling simultaneous data interaction among ports of said IP cores through said direct interconnect structure,  
         [0022]     providing configurable bus width routing between said IP cores through the selectors of the direct interconnect structure, and  
         [0023]     simultaneously routing data among said IP cores and said plurality of logic blocks through the direct interconnect structure.  
         [0024]     Thus, the present invention provides a direct an efficient routing structure between complex IP cores as signal processors and memory incorporated in FPGA.  
         [0025]     Before undertaking the DETAILED DESCRIPTION OF THE INVENTION,below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; and the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. It should be noted that the functionality associated with any particular apparatus or controller may be centralized or distributed. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The present invention will be described with reference to and as illustrated by the accompanying drawings, in which like reference numerals represent like parts, and in which:  
         [0027]      FIG. 1A  illustrates an existing PRIOR ART structure of FPGA with embedded Random Access Memory according to U.S. Pat. No. 5,933,023.  
         [0028]      FIG. 1B  illustrates the block diagram of an existing PRIOR ART configurable memory array according to U.S. Pat. No. 6,104,208.  
         [0029]      FIG. 1C  illustrates the PRIOR ART multifunction tile in accordance with U.S. Pat. No. 6,573,749;  
         [0030]      FIG. 2  illustrates the improved FPGA in accordance with the present invention;  
         [0031]      FIG. 3  illustrates the distribution of signals in the sub blocks of the memory block in accordance with the instant invention;  
         [0032]      FIG. 4  illustrates the distribution of signals in the sub blocks of the signal-processing block in accordance with the instant invention;  
         [0033]      FIGS. 5 and 6  illustrate the input matrices of the direct interconnect structure according to the instant invention;  
         [0034]      FIG. 7A  illustrates the input port of the signal-processing block being driven by the memory block;  
         [0035]      FIG. 7B  illustrates the simultaneous routing between the memory block and the signal-processing block′ 
         [0036]      FIG. 7C  illustrates the configurable bus width routing between the signal processing block and the memory block;  
         [0037]      FIG. 8A  illustrates the data routing from the output port of the signal-processing block to the first input port of the memory block;  
         [0038]      FIG. 8B  illustrates the data routing from the output port of the signal-processing block to the second input port of the memory block;  
         [0039]      FIG. 9  illustrates the bi-directional data interaction between the memory and signal-processing block; and  
         [0040]      FIG. 10  illustrates the multi port connectivity among the memory, signal processing block and logic block.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]      FIGS. 2 through 10 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged FPGA or like circuitry.  
         [0042]      FIG. 1  has been described under the heading ‘Background of the Invention’.  
         [0043]     The complex IP cores (hereafter referred as memory block and DSP block) that are connected through the Direct Interconnect structure are implemented in the FPGA are shown in  FIG. 2 . The figure shows that the size of the memory block (RAM block) is 18 K bits as, which comprises 16K data bits and 2K parity bits. The parity bits are available only in cross modes greater than or equal to 8. In the center of the FPGA is a plurality of Reconfigurable Logic Blocks (RLBs), separated periodically by columns of RAM blocks followed by the DSP blocks for providing routing between the Configurable Logic Blocks in FPGA. The figure also illustrates one column each of the RAM block and the DSP block. The RAM and DSP blocks span the height of eight Reconfigurable Logic Blocks. Signals are exchanged between RAM blocks and the DSP blocks by using the Direct Interconnect structure as shown in the  FIG. 2 . The Direct Interconnect structure comprises a configurable routing structure and hardwired interconnect structure for providing direct routing with minimized delay. Hardwired interconnects in the direct routing structure obviate the routing delay that would have been caused by routing the IP cores through the conventional switch matrix structure. The configurable routing structure is elaborated with reference to  FIGS. 5 and 6  in the document. RAM Block is configured to operate in multiple modes as a 512×32 array or a 1028×16 array.  
         [0044]     The RAM blocks illustrated in  FIG. 2  are dual port RAM blocks with each of the ports individually configurable in multiple modes. Since, said RAM block can be used as 16K×1 array, the total number of address bits required to address the RAM block is  14 . Thus, there are 28 address bits for the two ports of the memory and they operate as a single array for the two ports. Further, the total number of data bits for each port is  32 .  
         [0045]     The RAM block comprises sub blocks ( 301  to  308 ) are shown in  FIG. 3 . These sub blocks interact with the multiple switch boxes of the general-purpose routing structure besides being connected to the DSP block through the Direct Interconnect structure. The I/O port structure of the RAM block comprises two input ports (Ports A and B) and an output port. The Conventional signals in said RAM block have not been illustrated for the sake of simplicity. The address bits are designated by variables ADD_A and ADD_B for port A and port B respectively, wherein the number following the variables specifies the order of address bits. The data input bits are designated by variables DI_A and DI_B respectively and the data output bits are designated by DO_A and DO_B for signals A and B respectively.  
         [0046]     The DSP block comprises a plurality of sub blocks ( 401  to  408 ) and an I/O port structure comprising three input ports and an output port as shown in  FIG. 4 . Signals A and B are 18 bit wide, whereas signal C is 36 bit wide and the output bus is also 36 bits wide. Conventional signals in said DSP block have not been shown for the sake of simplicity. The Data Input bits are designated as DI and the number following them specifies the order of the data bits. The data output bits are designated as DO.  
         [0047]     The configurable routing structure is herein ( FIG. 5 ) described with reference to one sub block of the memory (RAM) block. The configurable routing structure comprises a selector (multiplexer) structure, wherein the selector structure comprises a plurality of logic selectors thus embodying a discrete selector structure. The selector structure in  FIG. 5  comprises four logic selectors of size nX 3 , wherein n equals the number of inputs to the logic selectors in the selector structure. The select lines function for the multiplexers are provided by the configuration bits in the FPGA. The distribution of signals in the logic selectors is such that the address inputs for port A and B of the memory are distributed in the four logic selectors. It is therefore observed that all these signals can be routed simultaneously with the help of Direct Interconnects. These addresses can be generated in the reconfigurable logic blocks adjacent to the RAM block and can be routed through the Direct Interconnects.  
         [0048]     The RAM block described here can be configured in any of the following modes: nX 1 , nX 2 , n X 4 , n X 8 , n X 16 , n X 32 , where n designates the number of bits in the array. It is further observed that in all these cases the lower data bits ( 0  to  15 ) are used in all the cases while the upper data ( 16  to  31 ) bits are used only in the nX 32  mode.  
         [0049]     Above said configurable bus width is achieved by using a discrete multiplexing logic (plurality of multiplexers) in the configurable routing structure. The upper data bits of port B and the lower data bits of port A are multiplexed to form one combination. Similarly, the upper data bits of port A and the lower data bits of port B are multiplexed together for providing a multi-port bi-directional data interaction among the IP cores and the configurable logic blocks in the FPGA.  
         [0050]     The stated distribution of signals implies that the lower data bits of both the ports can be routed simultaneously into the RAM block using the Direct Interconnects without stressing the general purpose routing resources. Further, the  32  data bits of any one port (A or B) can be routed simultaneously using the Direct Interconnect Structure. The data bits may be generated in the logic blocks adjacent to the RAM blocks or may be computed in the DSP block also adjacent to the RAM block.  
         [0051]      FIG. 6  shows the configurable routing structure interacting with a sub block of the DSP block. The routing structure herein described is similar to the routing structure of the RAM block and comprises four logic selectors of size nx 2  and nx 3 . The routing structure receives inputs from the memory block and the DSP block. The DSP block takes three inputs namely, A, B and C of width  18 ,  18  and  36  respectively and operates on these signals and gives the following combination of output signals. 
 Out=(sigma)  A*B    Or  Out= A*B+C    
         [0052]      FIGS. 7A, 7B  and  7 C illustrate the method in which both A and B port outputs of RAM block can drive the A and B port inputs of the DSP block. The port names herein prefixed by DIs indicate the data input ports and those prefixed by DOs indicate data output ports.  FIG. 7A  shows the connectivity between the two bits each of ports A and B of the signal processor and memory.  FIG. 7B  shows that the B and C inputs of the DSP block are fed simultaneously.  FIG. 7C  shows that the 32 data bits of input C of the DSP block can be fed by the RAM block using the Direct Interconnect structure described in  FIG. 6 .  
         [0053]      FIG. 8A and 8B  show the routing combinations by which the DSP block outputs can feed the memory block address and data inputs. The flexible address bus accessibility in the figure further illustrating the configurable bus width routing. The port names (A, B) in above said figures that are prefixed by ADD signify the address inputs of the memory block, whereas the port names prefixed by DIs signify the data inputs of the memory block. The bi-directional connectivity between the DSP block and the memory block ensures a faster and efficient routing structure, which is essential for effective implementation of digital signal processing applications.  
         [0054]     Above said routing combinations are explained explicitly as follows: 
        1) All the data bits of A, and all the data bits of B of the DSP block can be simultaneously routed from the memory block to the DSP block via Direct Interconnects.     2) All the data bits of A and the lower data bits of C of the DSP block can be routed form the RAM block to the DSP block.     3) All the data bits of C (except the last four bits i.e. parity bits) can be routed to the DSP block from the RAM block.     4) All the address bits of port A and port B of the RAM block can be simultaneously routed from the adjacent logic block.     5) All the data input bits of port A and port B of the RAM block can be simultaneously routed from the adjacent logic blocks.     6) All the outputs of DSP block (except for the last four bits) may drive the port A data input bits of RAM block.     7) All the outputs of DSP block (except for the last four bits) may drive the port B data input bits of RAM block.     8) All these signals may also be routed form the adjacent logic block via the Direct Interconnect structure.        
 
         [0063]     The bi-directional data routing between the memory and the signal-processing block is further explained using  FIG. 9 . The plurality of logic selectors in the Direct Interconnect structure enable the bi-directional routing between complex IP cores.  
         [0064]     The discrete structure of the logic selectors is significant in providing configurable bus width connectivity between the IP cores.  
         [0065]     The DIs that signify the data inputs in the signal processing block are routed through the direct interconnect structure to the DOs of the memory block and are further routed to the logic block ( FIG. 10 ), the logic block thus facilitating the minimal delay multiport data interaction among the IP cores (memory and signal processor) and the plurality of the logic blocks.  
         [0066]     It is therefore observed that implementation of the network of Direct Interconnects between the RAM blocks, DSP blocks and the Reconfigurable Logic Blocks not only offer fast and efficient data exchange between them but also integrates these blocks to the core. This structure is significant in complex Digital Signal Processing Applications where the data computed in the DSP block needs to be stored in memory or the coefficients of filters are stored in memory and are required in the DSP block for computation. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.