Abstract:
The invention relates to an intra-tile buffering system for a field programmable gate array. The field programmable gate array comprises a field programmable gate array tile comprising a number of rows and a number of columns. Each row has a left end and a right end, and each column has a top end and a bottom end. Each row comprises a plurality of functional groups with an interface group located at said right end and said left end. Each column comprises a plurality of functional groups with an interface group located at said top end and said bottom end. A primary routing structure is coupled to said functional groups and interface groups and configured to receive primary output signals, route primary output signals within said at least one field programmable gate array tile, and provide primary input signals to said functional groups and interface groups. Each functional group is configured to receive a primary input signal, perform a logic operation, and generate a primary output signal. Each interface group is configured to transfer signals from said primary routing structure to outside of said at least one field programmable gate array tile, and includes a plurality of input multiplexers configured to select signals received from outside of said at least one field programmable gate array tile and provide signals to the primary routing structure inside said at least one field programmable gate array tile. Said primary routing structure comprises a horizontal bus coupled to each row of functional groups, a vertical bus coupled to each column of functional groups, a horizontal buffer coupled to each horizontal bus and spaced every Nth column of functional groups, where N is an integer, and a vertical buffer coupled to each horizontal bus and spaced every Mth row of functional groups, where M is an integer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosed system relates to field-programmable gate arrays (FPGAs), and more particularly, to a field programmable gate array (FPGA) tile intra-tile buffer system. 
     2. Description of the Related Art 
     A field-programmable gate array (FPGA) is an integrated circuit (IC) that includes a two-dimensional array of general-purpose logic circuits, called cells or logic blocks, whose functions are programmable. The cells are linked to one another by programmable buses. The cell types may be small multifunction circuits (or configurable functional blocks or groups) capable of realizing Boolean functions of a few variables. The cell types are not restricted to gates. For example, configurable functional groups (“FGs”) typically include memory cells and connection transistors that may be used to configure logic functions such as addition, subtraction, etc., inside of the FPGA. A cell may also contain at least one flip-flop. Some types of logic cells found in FPGAs are those based on multiplexers and those based on programmable read only memory (PROM) table-lookup memories. Erasable FPGAs can be reprogrammed repeatedly. This technology is convenient when developing and debugging a prototype design for a new product and for small-scale manufacture. 
     FPGAs typically include a physical template that includes an array of circuits, sets of uncommitted routing interconnects, and sets of user programmable switches associated with both the circuits and the routing interconnects. When these switches are properly programmed (set to on or off states), the template or the underlying circuit and interconnect of the FPGA is customized or configured to perform specific customized functions. By reprogramming the on-off states of these switches, an FPGA can perform many different functions. Once a specific configuration of an FPGA has been decided upon, it can be configured to perform that one specific function. 
     The user programmable switches in an FPGA can be implemented in various technologies, such as ONO antifuse, M-M antifuse, SRAM memory cell, Flash EPROM memory cell, and EEPROM memory cell. FPGAs that employ fuses or antifuses as switches can be programmed only once. A memory cell controlled switch implementation of an FPGA can be reprogrammed repeatedly. In this scenario, an NMOS transistor is typically used as the switch to either connect or disconnect two selected points (A, B) in the circuit. The NMOS&#39; source and drain nodes are connected to points A, B respectively, and its gate node is directly or indirectly connected to the memory cell. By setting the state of the memory cell to either logical “1” or “0”, the switch can be turned on or off and thus point A and B are either connected or disconnected. Thus, the ability to program these switches provides for a very flexible device. 
     FPGAs can store the program that determines the circuit to be implemented in a RAM or PROM on the FPGA chip. The pattern of the data in this configuration memory (“CM”) determines the cells&#39; functions and their interconnection wiring. Each bit of CM controls a transistor switch in the target circuit that can select some cell function or make (or break) some connection. By replacing the contents of CM, designers can make design changes or correct design errors. The CM can be downloaded from an external source or stored on-chip. This type of FPGA can be reprogrammed repeatedly, which significantly reduces development and manufacturing costs. 
     In general, an FPGA is one type of programmable logic device (PLD), i.e., a device that contains many gates or other general-purpose cells whose interconnections can be configured or “programmed” to implement any desired combinational or sequential function. As its name implies, an FPGA is “field-programmable”, meaning that the device is generally programmed by designers or end users “in the field” via small, low-cost programming units. This is in contrast to mask programmable devices which require special steps in the IC chip-manufacturing process. 
     A field-programming unit typically uses design software to program the FPGA. The design software compiles a specific user design, i.e., a specific configuration of the programmable switches desired by the end-user, into FPGA configuration data. The design software assembles the configuration data into a bit stream, i.e., a stream of ones and zeros, that is fed into the FPGA and used to program the configuration memories for the programmable switches or program the shift registers for anti-fuse type switches. The bit stream creates the pattern of the data in the configuration memory CM that determines whether each memory cell stores a “1” or a “0”. The stored bit in each CM controls whether its associated transistor switch is turned on or off. End users typically use design software to test different designs and run simulations for FPGAs. 
     When an FPGA that has been programmed to perform one specific function is compared to an application specific integrated circuit (ASIC) that has been designed and manufactured to perform that same specific function, the FPGA will necessarily be a larger device than the ASIC. This is because FPGAs are flexible devices that are capable of implementing many different functions, and as such, they include excess circuitry that is either not used or could be replaced with hard-wired connections when performing one specific function. Such excess circuitry generally includes the numerous programmable transistor switches and corresponding memory cells that are not used in implementing the one specific function, the memory cells inside of functional groups, and the FPGA programming circuitry. This excess circuitry is typically eliminated in the design of an ASIC that makes the ASIC a smaller device. An ASIC, on the other hand, is not a flexible device. In other words, once an ASIC has been manufactured it cannot be reconfigured to perform a different function, which is possible with an FPGA. 
     Designers of FPGAs (as well as other PLDs) often provide their circuit designs to IC manufacturers who typically manufacture the FPGAs in two different ways. First, an FPGA design may be manufactured as its own chip with no other devices being included in the IC package. Second, an FPGA design may be embedded into a larger IC. An example of such a larger IC is a system on a chip (SOC) that includes the embedded FPGA as well as several other components. The several other components may include, for example, a microprocessor, memory, arithmetic logic unit (ALU), state machine, etc. In this scenario the embedded FPGA may be only a small part of the whole SOC. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention relates to an intra-tile buffering system for a field programmable gate array. The field programmable gate array comprises a field programmable gate array tile comprising a number of rows and a number of columns. Each row has a left end and a right end, and each column has a top end and a bottom end. Each row comprises a plurality of functional groups with an interface group located at said right end and said left end. Each column comprises a plurality of functional groups with an interface group located at said top end and said bottom end. A primary routing structure is coupled to said functional groups and interface groups and configured to receive primary output signals, route primary output signals within said at least one field programmable gate array tile, and provide primary input signals to said functional groups and interface groups. Each functional group is configured to receive a primary input signal, perform a logic operation, and generate a primary output signal. Each interface group is configured to transfer signals from said primary routing structure to outside of said at least one field programmable gate array tile, and includes a plurality of input multiplexers configured to select signals received from outside of said at least one field programmable gate array tile and provide signals to the primary routing structure inside said at least one field programmable gate array tile. Said primary routing structure comprises a horizontal bus coupled to each row of functional groups, a vertical bus coupled to each column of functional groups, a horizontal buffer coupled to each horizontal bus and spaced every Nth column of functional groups, where N is an integer, and a vertical buffer coupled to each horizontal bus and spaced every Mth row of functional groups, where M is an integer. 
     A better understanding of the features and advantages of the present disclosed system will be obtained by reference to the following detailed description of the disclosed system and accompanying drawings which set forth an illustrative embodiment in which the principles of the disclosed system are utilized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustrating a field programmable gate array. 
     FIG. 2 is a schematic illustrating a more detailed view of one tile shown in FIG.  1 . 
     FIG. 3 is a schematic illustrating a detailed view of a side-by-side pair of functional groups. 
     FIG. 4 is a schematic illustrating a detailed view the inner components and connections of a functional group. 
     FIG. 5 is a schematic illustrating a detailed view of a look up table which comprises a functional group. 
     FIG. 6 is a schematic illustrating an interface group. 
     FIG. 7 is a schematic illustrating two side-by-side interface groups. 
     FIG. 8 a  is a schematic illustrating the horizontal intra-tile buffers and the vertical intra-tile buffers on a portion of one field programmable gate array tile. 
     FIG. 8 b  is a schematic illustrating routing resources between functional groups. 
     FIGS. 9 a  and  9   b  are schematics illustrating the programmable interconnectors comprising the CL turn areas. 
     FIGS. 10 a  and  10   b  are schematics illustrating the intra-tile horizontal buffers. 
     FIGS. 11 a  and  11   b  are schematics illustrating the intra-tile vertical buffers. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, an overall view of one embodiment of the disclosed system is shown. Field-programmable gate array (FPGA)  250  has IO &amp; PAD ring  254  on the outer perimeter. RAM blocks  258  are between IO &amp; PAD ring  254  and boundary scan chains  262 . Circuitry within and including boundary scan chains  262  forms a core to which RAM may be added. This core is also easily adapted to other configurations. 
     In this embodiment four FPGA tiles  263  are shown arranged in a 2 by 2 matrix. Built-in self-test interface module (“BIST”)  264  is adjacent to FPGA tiles  270 . Configuration interface  266  is a configuration control module that receives the bitstream program into its configuration RAM. Joint test action group (“JTAG”) interface  268  is a module that is an access point that allows for high-level test control. 
     FIG. 2 is a schematic illustrating a more detailed view of one FPGA tile  263  from FIG.  1 . In one embodiment, each FPGA tile is made up of a plurality of pairs of functional groups (FGs—each pair referred to as a “FG×2”)  274  arranged in a side-by-side manner. FGs are small multifunction circuits that are capable of realizing many Boolean functions. The FGs include look-up tables (LUTs) and other circuits capable of realizing Boolean functions, as well as memory cells that are used to configure logic functions such as addition, subtraction, etc. 
     Still referring to FIG. 2, in one embodiment FG×2s  274  are arranged in a 16 by 8 array of FG×2s. Since an FG×2 is a pair of side FGs, then this array is equivalent to a 16 by 16 array of FGs. Each row containing 8 FG×2s comprise  16  FGs because there are 2 side by side FGs in each FG×2. Please refer to FIG. 3 for a more detailed view of FG×2  274 . 
     Around the outer perimeter of the 16×8 FG×2 array are interface groups (“IGs”)  286 . IGs  286  provide an interface for FPGA tiles  270  to other FPGA tiles or devices, or to pad rings for connecting the FPGA tiles to IC package pins. In general, the logic structure of the FPGA tile is provided by the FGs and the IGs. The IGs are arranged around the FG×2 array as follows: There are two columns of IGs  286 , one on the left side and one on the right side of the FG×2 array. There are two rows  282  of pairs of IGs referred to as IG×2 located on the top side and bottom side of the FG×2 array. 
     Also included in the FPGA tiles, but not shown in FIG. 2, are several horizontal and vertical regular routing buses, routing interconnect areas, switching transistors, and global signal distribution routing structure, all of which will be discussed below. 
     FIG. 3 illustrates a more detailed view of FG×2  274 . Two FGs  294  and  298  comprise FG×2  274 . Each of FGs  294  and  298  are configured to receive inputs from the following routing resources: EUI[ 0 : 4 ], EBI[ 0 : 4 ], GG[ 0 : 7 ], SL[ 0 : 7 ] and CI. Both of FGs  294  and  298  are also configured to send outputs through the following resources: CO, Y[ 0 : 4 ], and LINT ports. The LINT ports carry a secondary routing signal. Between FGs  294  and  298  is a vertical channel containing vertical bus VA  291  which carries the following routing resources: VT[ 0 : 11 ] [ 0 : 4 ], VSL[ 0 : 7 ], VLL[ 0 : 9 ], and VCL[ 0 : 9 ]. The convention of [ 0 : 11 ] [ 0 : 4 ] means that there are 12 ( 0  through  11 ) sets of 5 ( 0  through  4 ) routing resources. Adjacent to VA bus  291  is cross bus XA  293 . The routing within XA  293  is described in detail in FIG.  10 . Horizontal busses HA  295  and  297  carry the following routing resources: HT[ 0 : 11 ] [ 0 : 4 ], HSL[ 0 : 7 ], HLL[ 0 : 9 ], HCL[ 0 : 9 ], and HFT[ 0 : 41 ]. 
     FIG. 4 illustrates a schematic providing a more detailed view of FGs from FIG.  3 . Each FG  304  may include four logic units (“LUBs”)  308 ,  312 ,  316 ,  320 . Each LUB is coupled to routing resource Y[ 0 ] through Y[ 3 ] respectively. LUBs is  308 ,  312 ,  316  and  320  provide Boolean functions and logic operations of FG  304 . Each of the LUBs  308 ,  312 ,  316  and  320  includes several inputs on which Boolean functions and logic operations are performed. As shown, each of LUBs  308 ,  312 ,  316  and  320  includes twenty-four such inputs (not including the CI routing resource), but it should be understood that the number of inputs may vary in accordance with the invention. Specifically, each of LUBs  308 ,  312 ,  316  and  320  receives signals through input ports UI[ 0 : 4 ] and BI[ 0 : 4 ] which correspond to signals received through regular input ports EUI[ 0 : 4 ] and EBI[ 0 : 4 ]. Also, each of LUBs  308 ,  312 ,  316  and  320  receives signals through input ports GI[ 0 : 5 ] and JI[ 0 : 7 ]. The input signals via input port JI[ 0 : 7 ] include two output signals JO and JPO from each of LUBs  308 ,  312 ,  316  and  320 . Thus, two output signals JO and JBO of each of LUBs  308 ,  312 ,  316  and  320  are fed back to the inputs by way of JI[ 0 : 7 ]. 
     Input signals GI[ 0 : 5 ] are selected from the SL[ 0 : 7 ] and GG[ 0 : 7 ] routing resources. Sixteen-to-one multiplexer  324  selects one of the inputs from routing resources SL[ 0 : 7 ] and GG[ 0 : 7 ] and makes four copies of the selected input, as indicated by the slash “/” and associated number “4”. Thus the routing resource GI[ 0 : 3 ] is shown exiting multiplexer  324 . Routing resource GG[ 7 ] and CI are added to the GI[ 0 : 3 ] bus, thereby forming a GI[ 0 : 5 ] bus. 
     Each of LUBs  308 ,  312 ,  316  and  320  also includes a clock/enable/preset/clear (“C/E/P/C”) input. The C/E/P/C input is used to control a flip-flop included inside each of LUBs  308 ,  312 ,  316  and  320 . The C/E/P/C input signal is generated by selection circuitry, shown in the dashed lines of box  326 . The C/E/P/C selection circuitry receives inputs UI[ 0 : 4 ], BI[ 0 : 4 ], JI[ 0 : 7 ], and GI[ 0 ; 5 ] at each of twenty-four-to-one multiplexers  328 ,  332 ,  336  and  340 . Each multiplexer  328 ,  332 ,  336  and  340  selects one signal from buses UI[ 0 : 4 ], BI[ 0 : 4 ], JI[ 0 : 7 ], and GI[ 0 : 5 ]. Each signal selected by each multiplexer  328 ,  332 ,  336  and  340  is sent to nine-to-one multiplexers  344 ,  348 ,  352 , and  356  via routing resources GX[ 0 ], GX[ 1 ], GX[ 2 ], and GX[ 3 ] respectively. Each of nine-to-one multiplexers  344 ,  348 ,  352 , and  356  also receives an input from the GG[ 0 : 7 ] routing resource. The signal selected by multiplexer  344  becomes clock signal CLK, the signal selected by multiplexer  348  becomes preset signal PRSTN (“P”), the signal selected by multiplexer  352  becomes clear signal CLRN(“C”), and the signal selected by multiplexer  356  becomes enable signal E. The use of multiplexers  344 ,  348 ,  352  and  356  allows any of the signals GX[ 0 : 3 ], GG[ 0 : 7 ], and ground to be selected as one of the C/E/P/C signals. 
     The GG[ 0 : 7 ] bus is an inter-tile global bus that is coupled to every FG in all FPGA tiles. The signals in the GG[ 0 : 7 ] bus are often selected as the C/E/P/C signals. It should be well understood, however, that the illustrated C/E/P/C selection circuitry from FIG. 4 is just one embodiment of such a selection circuit and that various different designs of C/E/P/C selection circuit in box  326  may be used to select various different signals in accordance with the invention. 
     It should be understood, however, that various different designs of the circuitry discussed above may be used to select various different numbers of signals for LUBs  308 ,  312 ,  316  and  320  in accordance with the invention. In one embodiment, LUBs  308 ,  312 ,  316  and  320  are all of the same design, but in another embodiment they are not of the same design. 
     FIG. 5 illustrates a more detailed view of one of LUBs  308 ,  312 ,  316 , and  320  from FIG.  4 . LUB  358  includes two look-up tables (“LUTs”)  362  and  366 . Each LUT  362  and  366  comprises three inputs A, B, C, one output Y, and several internal memory cells (not shown). LUT  362  also comprises output CO. LUTs  362  and  366  are configured by programming internal memory cells (not shown), and the setting of the internal memory cells taken together provides a specific configuration for each of LUTs  362  and  366 . Configuration data used to program the internal memory cells is generated by design software. Once a specific configuration of the internal memory cells is decided upon, inputs A, B, C may be used to generate output Y in accordance with the desired logic function. 
     Inputs A, B, C of the LUT  362  are provided by twenty-four-to-one multiplexers  370 ,  374  and  378 , respectively, and inputs A, B, C of LUT  366  are provided by twenty-four-to-one multiplexers  382 ,  386  and  390 , respectively. Each of multiplexers  370 ,  374 ,  378 ,  382 ,  386 ,  390  receives as inputs buses EUI[ 0 : 4 ], EBI[ 0 : 4 ], JI[ 0 : 7 ], and GI[ 0 : 5 ], comprising twenty four inputs in total. Three signals are selected from these twenty-four signals as inputs A, B, C for each of LUTs  362  and  366 . 
     When only a three input LUT is needed, one of LUTs  362  and  364  is used. In one embodiment, LUT  362  is used while LUT  364  is not used. The Y output of LUT  362  can be sent directly to the JO output of LUB  358 , or the Y output of LUT  362  can be sent to the Y output of LUB  358  by using two-to-one multiplexer  394  to select the Y output of LUT  362 . Additionally, the Y output of LUT  362  can be sent to the JPO output of the LUB  358  by using two-to-one multiplexer  398  to select the Y output of the LUT  362  and two-to-one multiplexer  402  to select the output of multiplexer  398 . Thus, multiplexers  394 ,  398  and  402  can be used to send the Y output of LUT  362  to any of the outputs Y, JO, JPO of the LUB  358 . 
     Additionally, when two, three input LUTs are needed, LUT  362  and  366  can be used independently as three input LUTs. The Y output of LUT  362  can be sent directly to the JO output of LUB  358 , or the Y output of the LUT  362  can be sent to the Y output of the LUB  358  by using two-to-one multiplexer  394  to select the Y output of LUT  362 . The Y output of LUT  366  can be sent directly to the JPO output of LUB  358 , or the Y output of the LUT  366  can be sent to the Y output of the LUB  358  by using two-to-one multiplexer  394  to select the output of two-to-one multiplexer  402 , which can select the output of two-to-one multiplexer  398 , which can select the Y output of the LUT  366 . 
     As stated previously, one purpose of including two LUTs in the LUB is so that they can be used together to provide a four-input LUT. Specifically, the Y output of LUT  362  and the Y output of LUT  366  are connected to the inputs of two-to-one multiplexer  398 . In order to simulate a single, four-input LUT, two-to-one multiplexer  406  selects the signal from twenty-four-to-one multiplexer  390  as input C to LUT  362 . Two-to-one multiplexer  410  selects the signal from twenty-four-to-one multiplexer  378  as the fourth input to LUT  362 . Thus, both LUTs  362  and  366  receive the first, second and third inputs at their A, B, and C inputs and multiplexer  410  is programmed to select the fourth input and provide it to the control input of multiplexer  398 . 
     According to well-known Boolean logic techniques and the Shannon Expansion, connecting three-input LUTs  362  and  366  in this manner will simulate a single four-input LUT with the result being generated at the output of multiplexer  398 . The output of multiplexer  398  can be provided to the JPO output of LUB  358  by way of multiplexer  402  or to the Y output of LUB  358  by way of the multiplexers  394  and  402 . 
     FIG. 6 illustrates a more detailed view of the routing resources adjacent to IGchan  286  of FIG.  2 . Vertical bus (VAL)  418  and horizontal bus (HAL)  415  are shown adjacent to the IGchan  414 . Positioned diagonal to Igchan  414  is cross-bus (XAL)  417 . IGchan  414  has the following inputs: PI[ 0 : 13 ], CO[ 0 : 9 ], GG[ 0 : 7 ], SL[ 0 : 7 ] and the following outputs: PO[ 0 : 13 ], LINT, and CI[ 0 : 9 ]. The CO[ 0 : 9 ], GG[ 0 : 7 ], and SL[ 0 : 7 ] inputs are coupled to HAL bus  415 . The CI[ 0 : 9 ] and LINT outputs are coupled to the VAL bus  418 . 
     FIG. 7 illustrates a more detailed view of a typical IG×2 as first shown in FIG.  2 . The IG×2  420  has two IGs  424  and  428 . Between IGs  424  and  428  is vertical bus VAT  432 . Below and adjacent to each of IGs  424  and  428  are horizontal busses HAT  436  and  440 . Adjacent to VAT  432  and HAT busses  436  and  440  is cross bus XAT  444 . Each of IGs  424  and  428  has outputs PO[ 0 : 13 ], CI[ 0 : 9 ], and LINT. Each of IGs  424  and  428  has inputs PI[ 0 : 13 ], CO[ 0 : 9 ], GG[ 0 : 7 ], and SL[ 0 : 7 ]. 
     FIG. 8 a  illustrates a portion of the plurality of functional groups comprising a FPGA tile, see FIG.  2 . Intra-tile horizontal buffers (“HBF”)  602  are horizontally spaced apart by four functional groups. Intra-tile vertical buffers (“VBF”)  606  are vertically spaced apart by four functional groups. Other spacing for the tile buffers may be used depending on design requirements. Horizontal routing resources HT[ 0 : 11 ] [ 0 : 4 ], HLL[ 0 : 9 ], HCL[ 0 : 9 ], and HSL[ 0 : 7 ] are buffered at HBF  602 . 
     Vertical routing resources VT[ 0 : 11 ] [ 0 : 4 ], VLL[ 0 : 9 ], VCL[ 0 : 9 ], and VSL [ 0 : 7 ] are buffered at VBF  606 . Details of HBF  602  and VBF  606  are illustrated below. 
     A primary routing structure comprises the horizontal routing resources and the vertical routing resources. The routing resources VCL[ 0 : 9 ] and HCL[ 0 : 9 ] intersect at programmable interconnect  610 . 
     FIG. 8 b  is a schematic illustrating routing resources between functional groups. Routing resource HT[ 0 : 11 ] [ 0 : 4 ] is shown as 12 ( 0  through  11 ) sets of 5 ( 0  through  4 ) routing resources. HT[ 0 : 11 ] [ 0 : 4 ] intersect the routing resource EUI and EBI at SW 1   603 . Routing resources EUI and EBI connect to functional groups, for example functional groups  294  and  298  in FIG.  3 . Routing resources HLL[ 0 : 9 ], HCL[ 0 : 9 ] and HSL[ 0 : 7 ] are also shown. HSL[ 0 : 7 ] is coupled to routing resource SLI[ 0 : 7 ]. Each SW 1   603  comprises programmable interconnects. In one embodiment, functional groups may transmit data to each other with EUI and EBI routing resources and through HLL[ 0 : 9 ] routing resources, as indicated by programmable interconnects  603  at the intersection of EUI, EBI and HLL[ 0 : 9 ] routing resources. 
     FIG. 9 a  is a schematic illustrating programmable interconnect  610  between VCL[ 0 : 9 ] and HCL[ 0 : 9 ], see FIG. 8 a . HCL[ 0 ] intersects with VCL[ 0 ], HCL[ 1 ] intersects with VCL[ 1 ], HCL[ 2 ] intersects with VCL[ 2 ], and so on, until HCL[ 9 ] intersects with VCL[ 9 ]. 
     FIG. 9 b  is a schematic illustrating intersection points  608  from FIG. 9 a . Each programmable interconnect in intersection point  608  from FIG. 9 a  comprising vertical track  611  driving horizontal track  613  with three-state buffer  609 . 
     FIG. 10 a  is a schematic illustrating a more detailed view of HBF  602  from FIG. 8 a . Each of the HT[ 0 : 11 ] [ 0 : 4 ], HSL[ 0 : 7 ] and HLL[ 0 : 9 ] tracks are segmented by buffer  614 . However, the HCL[ 0 : 9 ] tracks do not have a buffer that segments them. Buffer  618  couples together each of the HCL[ 0 : 9 ] with each of the HLL[ 0 : 9 ] tracks. For example, HLL[ 0 ] is segmented by buffer  614  and coupled through buffer  618  to HCL[ 0 ], which is not segmented. HLL[ 1 ] is segmented by buffer  614  and coupled through buffer  618  to HCL[ 1 ], which is not segmented, and so on, until HLL[ 9 ] is segmented by buffer  614  and coupled through buffer  618  to HCL[ 9 ], which is not segmented. 
     Because the HCL tracks are coupled in this way to a buffer, the HCL tracks may be referred to as a non-segmented, horizontal bus. The HLL may be referred to as the segmented, horizontal bus due to the buffer. Vertical buffers  618  also comprise the three-state bi-directional transistor configuration shown in FIG. 10 b.    
     FIG. 10 b  is a schematic illustrating three-state, bi-directional transistor configuration  619 . Configuration  619  represents buffers  614  and  618  from FIG. 10 a . Configuration  619  isolates signals on one side of the configuration from signals on the other side, allowing a single line to behave as if it were two separate lines. 
     FIG. 11 a  is a schematic illustrating a more detailed view of VBF  606  in FIG. 8 a . Each of the VT [ 0 : 11 ] [ 0 : 4 ], VSL[ 0 : 7 ] and VLL[ 0 : 9 ] tracks are segmented by bi-directional buffer  622 . However, the VCL[ 0 : 9 ] tracks do not have a buffer that segments them. Buffer  626  couples together each of the VCL[ 0 : 9 ] with each of the VLL[ 0 : 9 ] tracks. For example, VLL[ 0 ] is segmented by buffer  622  and coupled through buffer  626  to VCL[ 0 ], which is not segmented. VLL[ 1 ] is segmented by buffer  622  and coupled through buffer  626  to VCL[ 1 ], which is not segmented, and so on, until VLL[ 9 ] is segmented by buffer  622  and coupled through buffer  626  to VCL[ 9 ], which is not segmented. 
     Because the VCL tracks are coupled in this way to a buffer, the VCL tracks may be referred to as a non-segmented, vertical bus. The VLL tracks may be referred to as the segmented, vertical bus due to the buffer. Each of buffers  626  also comprises a three-state bi-directional transistor configuration illustrated in FIG. 11 b.    
     FIG. 11 b  is a schematic illustrating three-state, bi-directional transistor configuration  639 . Configuration  639  represents buffers  622  and  626  from FIG. 11 a . Configuration  639  isolates signals on one side of the configuration from signals on the other side, allowing a single line to behave as if it were two separate lines. 
     Functional groups are separated from one another by horizontal buses HA and vertical buses VA (see FIG.  3 ). Cross bus XA connects VA and HA buses with routing resources HT[ 0 : 11 ] [ 0 : 4 ], HSL[ 0 : 7 ], HLL[ 0 : 9 ], HCL[ 0 : 9 ], VT[ 0 : 11 ] [ 0 : 4 ], VSL[ 0 : 7 ], VLL[ 0 : 9 ], and VCL[ 0 : 9 ]. Within a FPGA tile, in one embodiment every fourth functional group is separated from the next four functional groups by a buffer, in both the horizontal and vertical directions (see FIG. 8 a ). A matrix comprised of N-by-N functional groups defines a local signaling group within which signals may be transmitted, between functional groups, over one or both of HLL[ 0 : 9 ] and HCL[ 0 : 9 ] for horizontal transmissions and one or both of VLL[ 0 : 9 ] and VCL[ 0 : 9 ] for vertical transmissions, or a combination of horizontal and vertical transmission. 
     Signals may be transmitted between functional groups when the functional groups are not in one local signaling group by using routing resources HCL[ 0 : 9 ] and VCL[ 0 : 9 ] (see FIGS. 10 a  and  11   a ). Routing resources HCL[ 0 : 9 ] and VCL[ 0 : 9 ] are not segmented by buffers HBF and VBF, respectively, therefore signaling between local signaling groups may occur over those resources. 
     The routing interconnect areas includes transistor switches and memory cells at many intersections of signal lines, but not at all intersections. From this disclosure, it will be apparent to persons of ordinary skill in the art, however, that the specific number of lines in any of the routing buses may vary in accordance with the present disclosed system. Furthermore, it should be well understood that the specific number of lines in any of the signal buses may vary in accordance with the present disclosed system. 
     From this disclosure, it will be apparent to persons of ordinary skill in the art that various alternatives to the embodiments of the disclosed system described herein may be employed in practicing the disclosed system. It is intended that the following claims define the scope of the disclosed system and that structures and methods within the scope of these claims and their equivalents be covered thereby.