Abstract:
A floorplan for a reconfigurable chip uses slices adjacent to each of four corners of a region, each of the slices including tiles that contain multiple reconfigurable functional units including ALUs. The placement of the slices in the corners of their region allows for better and quicker interconnection between elements on the slices.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to reconfigurable chips. Reconfigurable chips are chips that can be configured to a number of different uses. A reconfigurable chip that recently has been found to be quite useful is a reconfigurable chip used to implement an algorithm, such as a communications system algorithm. Sections of the algorithm are swapped in and out of the reconfigurable chip as needed. 
     FIG. 1 shows a prior-art floorplan for such a reconfigurable chip. In floorplan  40  is shown an ASIC portion  42  which implements a central processor unit and other logic needed for the reconfigurable chip. Also shown is a reconfigurable fabric section  44  which implements the reconfigurable logic of the system. In one embodiment, the fabric  44  is divided into slices such as slice  46 . Each of the slices is composed of a number of tiles  48 . Each of the tiles contains a number of reconfigurable functional units, or data path units. These reconfigurable functional units preferably use a dedicated arithmetic logic unit (ALU). Preferably, the elements within a region such as slices and tiles are more interconnected than elements in different regions. 
     A disadvantage with the division of slices as shown in FIG. 1 is that the reconfigurable fabric portion  44  tends to be longer than it is wide. These long interconnections make it difficult to meet timing requirements, especially for connections between the ASIC portion  42  and the portions on the far side of a slice. The resistive/capacitive (RC) constant for these interconnection regions tends to be relatively high, producing a longer flight time with relatively slow rise and fall times resulting in a relatively high power dissipation. 
     It is desired to have an improved floorplan that improves on the timing for interconnection of elements on a reconfigurable chip. 
     SUMMARY OF THE PRESENT INVENTION 
     One embodiment of the present invention comprises a region on the reconfigurable chip including four slices, each of the slices being adjacent to a corner of the region. Each slice has multiple tiles; each tile has multiple reconfigurable logic units; and each reconfigurable logic unit includes an arithmetic logic unit. 
     By placing the slices adjacent to each corner of the region on the reconfigurable chip, the interconnection time between the reconfigurable logic units on the chip is reduced. Additionally, the regions with slices in the four corners have an aspect ratio closer to one than when elongated slices are used. 
     In one embodiment, the slices are rectangular. In another embodiment the slices are L-shaped to allow a center logic portion within the region. The regions described above have the advantage in that they can be placed within an even greater sized region of the floorplan. Four such regions can be put in the corners of an even greater region on the chip. The regions of the present invention are thus much more scalable for additional designs. 
     Another embodiment of the present invention uses a multiplexer receiving inputs from at least three reconfigurable logic units. The multiplexer is operably connected to an interconnect bus. Such an interconnection system using such multiplexer helps remove the tri-state buffers from the bus system and thus reduces the RC constant for this system and reduces the interconnection times. This multiplexer system has a slight downside in that it reduces some of the interconnection flexibility. However, in many cases, the interconnection speed benefit outweighs this disadvantage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a prior-art floorplan design for a reconfigurable logic chip; 
     FIG. 2 illustrates one example of a floorplan of a reconfigurable logic system of the present invention; 
     FIG. 3 illustrates another embodiment of a floorplan or region of a reconfigurable chip of the present invention; 
     FIG. 4 is a design using a multiple of the regions of FIG. 3 into a larger region; 
     FIGS. 5A and 5B are prior-art designs for the datapath used in a tile; 
     FIGS. 6A and 6B show designs for replacing datapath units within the tile; 
     FIG. 7 is a design of a reconfigurable functional unit including an arithmetical logic unit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 illustrates a design for a floorplan region for use in a reconfigurable logic chip. The region  50  includes slices  52 . Slices  52  include tiles  54 . The slices  52  are placed adjacent to the corners of the region  50 . This arrangement allows the entire region  50  to be more square-shaped with an aspect ratio closer to one. This also reduces the interconnection distances between many of the elements on different tiles of the reconfigurable chip. The ASIC elements can be placed in regions such as region  56  between the different slices. In one embodiment a crossbar switch or other switch  58  is used to interconnect the slices. 
     FIG. 3 illustrates an alternate embodiment of a region for a reconfigurable chip. Region  60  includes slice  62 . Slice  62  includes tile  64 . Using an L-shaped slice  62  has the advantage that it allows for a center ASIC region  66 ; it has the slight disadvantage that fewer of the tiles can be placed in each slice. In this example, three tiles are used in each slice rather than four tiles of the example of FIG.  2 . 
     Although this area is called a slice, it is clear from FIGS. 2 and 3 that these slices are preferably not elongated as shown in the prior art. Indeed, the terms “slice”, “tile”, and “region” are used in the present invention and claims merely to indicate different areas on the floorplan of a reconfigurable logic chip and are not meant in any further geometrically descriptive sense. 
     The regions of FIGS. 2 and 3 can be the entire reconfigurable chip or multiple regions can be arranged within a larger region. 
     FIG. 4 illustrates a system in which multiple regions  70  are placed within a larger region  72 , regions  70  including slices  74  and tiles  76 . Note that the regions of FIGS. 2 and 3, because of the aspect ratio closer to one and because of the relatively short interconnection distances between elements on the chip, tend to be quite scalable, meaning that they can be further connected together into a larger region for a reconfigurable chip. This means that a specific design for a reconfigurable chip can have a greater reuse in the next generation reconfigurable chips. 
     FIG. 5 illustrates a prior-art example of a tile structure  80 . This tile structure includes a configuration memory  82  along with a number of datapath units  84 , the datapath units being a reconfigurable functional unit preferably containing an arithmetic logic unit (ALU). The interconnection between the data path units in the tile is typically done by a bus structure such as that shown in FIG.  5 B, in which multiple tri-state drivers are connected to a bus. This embodiment of FIG. 5B has a disadvantage that the number of tri-state drivers further adds to the slowing of the transmission of signals across the bus  88 . 
     FIG. 6A illustrates an alternate embodiment of a tile structure  90 . One interconnection system is shown in FIG. 6B in which a multiplexer  92  is connected to more than three of the datapath units; in this case, all of the datapath units in the tile  90 . The output of the multiplexer  92  is sent to the tri-state buffer  94 . The bus  96  is connected to many fewer tri-state buffers and can thus speed up the interconnection of the system of the present invention due to the reduced RC constant for the bus  96 . Use of the multiplexer  92  reduces the flexibility of the bus  96 ; however, in many situations, the increase in speed compensates for this disadvantage. 
     FIG. 7 is a diagram of a reconfigurable functional unit or datapath unit  20 . The datapath unit includes input multiplexers  22  and  24 ; buffers  26  and  28 ; registers  32  and  34 ; shift register  36 ; logic  38 ; additional internal multiplexers; and ALU  30 . 
     The use of the ALU allows for distributive reconfigurable computing to be done on the reconfigurable chip. The reconfigurable functional units including the ALU are placed in tiles which are placed within slices which are placed within a region or regions on the reconfigurable chip. 
     It will be appreciated by those of ordinary skill in the art that the invention can be implemented in other specific forms without departing from the spirit or character thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is illustrated by the appended claims rather than the foregoing description, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced herein.