Abstract:
Presented herein is a system and method for byte slice based DDR timing closure. In one embodiment, there is presented a method for synthesizing/laying out a dual data rate memory, said method comprising synthesizing/laying out a portion of the dual data rate memory; replicating the portion; and placing the synthesized/laid out portion and the replicated portions in proximity to a corresponding plurality of pads.

Description:
RELATED APPLICATIONS 
     This application claims priority to “Byte Slice Based DDR Timing Closure”, Provisional Application for U.S. Patent, Ser. No. 60/495,585, filed Aug. 15, 2003, which is incorporated herein by reference in its entirety for all purposes. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     [Not Applicable] 
     MICROFICHE/COPYRIGHT REFERENCE 
     [Not Applicable] 
     BACKGROUND OF THE INVENTION 
     A dual data rate (DDR) memory is characterized by a data signal that provides bits of information during the rising edge of a clock signal as well as the falling edge of the DQS signal. Accordingly, 2 bits/cycle are possible. The data signal is to be sampled at 90 and 270 degrees phase shift from the DQS signal. 
     As the clock signal increases, such as from 100 MHz to 200 MHz, the time period shrinks from 10 ns to 5 ns. Skews that may be permissible for slower clocks become unacceptable for faster clocks. 
     Integrated circuits are generally designed using synthesis tools. The timing for data pins in a DDR memory are carefully measured and adjusted. However, as the number of data pins increases, the effort is also repeated. This leads to increased prefabrication period. 
     Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the invention as set forth in the remainder of the present application with reference to the drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     presented herein is a system and method for byte slice based DDR timing closure. 
     In one embodiment, there is presented a method for synthesizing/laying out a dual data rate memory, said method comprising synthesizing/laying out a portion of the dual data rate memory; replicating the portion; and placing the synthesized/laid out portion and the replicated portions in proximity to a corresponding plurality of pads. 
     In another embodiment, the portion comprises a plurality of input/outputs. 
     In another embodiment, the plurality of input/outputs comprises a byte lane. 
     In another embodiment, synthesizing/laying out the portion further comprises generating a macro, said macro synthesizing/laying out the portion. 
     In another embodiment, the macro comprises a plurality of cells, each of said cells corresponding to a particular one of the plurality of input/outputs. 
     In another embodiment, there is presented a computer readable media for synthesizing a dual data rate memory controller. The computer readable media stores a plurality of instructions. The plurality of instructions comprises receiving a macro representing a portion of the dual data rate memory controller; replicating the macro; and placing the macro and the replicated macros in proximity to a corresponding plurality of pads. 
     In another embodiment, the portion comprises a plurality of input/outputs. 
     These and other advantageous and novel features as well as details of illustrated embodiments will be more fully understood from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary dual data rate memory controller interface; 
         FIG. 2  is a flow diagram for synthesizing the dual data rate memory controller in accordance with an embodiment of the present invention; 
         FIG. 3  is a block diagram of a synthesized dual data rate memory controller portion in accordance with an embodiment of the present invention; and 
         FIG. 4  is a block diagram of an exemplary computer system in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , there is illustrated a block diagram describing an exemplary 64-bit dual data rate memory. The dual data rate memory controller is an integrated circuit comprising of say 64 data pins D( 0 ). . . D( 63 ), eight data strobe signal pins DQS( 0 ). . . DQS( 7 ), and eight data mask signals DQM( 0 ). . . DQM( 7 ). Each eight of the data pins, e.g., D( 0 ). . . D( 7 ), is associated with a particular one of the data strobe signal pins, e.g., DQS( 0 ), and a particular one of the data mask signals, e.g., DQM( 0 ). The eight data pins D( 0 ). . . D( 7 ), the associated data strobe signal DQS( 0 ), and the data mask signal DQM( 0 ), are collectively referred to as a byte lane. 
     The data signal pins D provide or receive data signals. The data signals are synchronized with a clock, such that the data signal pins D provide/receive a bit of information during both a high cycle and low cycle of the clock signal. Accordingly, during each clock cycle, each data pin D can either provide or receive two bits per clock cycle. 
     During a memory write, a memory controller provides the data signals to the data pins D; along with data strobe signals DQS. The data strobe signals DQS are shifted 90 degrees with respect to the data signals. The DDR memory latches the data signals at both the rising edge and the following edge of the DQS signal. 
     During a memory read, the DDR memory provides the DQS signals, DQS( 0 ). . . DQS( 7 ), along with the data signals D( 0 ). . . D( 63 ). The DQS signals are aligned with the data signals. 
     As the clock signal for the DDR memory becomes faster, timing skews that are acceptable for slower clocks signals become unacceptable for faster clocks signals. Thus, minimal timing skews between the data pins D are permissible. 
     Integrated circuits, such as DDR memory controllers are generally converted from RTL to gates/layout using synthesis/layout tools. During the design, the timing of data paths associated with the data pins D are carefully measured and adjusted. However, as in the present illustration, with 64 pins, the efforts increase. 
     Referring now to  FIG. 2 , there is illustrated a flow diagram for synthesizing a dual data rate memory controller in accordance with an embodiment of the present invention. At  205 , a portion of the dual data rate memory controller is synthesized. According to certain aspects of the invention, the portion can comprises, for example, a byte lane. The portion is synthesized and laid out such that the timing is measured and appropriate. 
     Additionally, according to certain aspects of the present invention, the portion of the dual data rate memory controller can be represented by what is known as a macro. The macro comprises a plurality of cells, each of which corresponds to a particular one of the data pins D. At  210 , the portions are replicated as needed. At  215 , each of the synthesized portion and the replication portions are placed in proximity to a corresponding plurality of pads. 
     Referring now to  FIG. 3 , there is illustrated a block diagram describing an exemplary synthesized DDR memory controller in accordance with an embodiment of the present invention. Each of the byte lanes is associated with a particular one of a plurality of macros  305 . Each of the macros is placed in proximity with pads  310 . 
     Referring now to  FIG. 4 , a representative hardware environment for practicing the present invention is depicted and illustrates a typical hardware configuration of a computer information handling system  58  in accordance with the subject invention, having at least one central processing unit (CpU)  60 . CpU  60  is interconnected via system bus  12  to random access memory (RAM)  64 , read only memory (ROM)  66 , and input/output (I/O) adapter  68  for connecting peripheral devices such as disc units  70  and tape drives  90  to bus  62 , user interface adapter  72  for connecting keyboard  74 , mouse  76  having button  67 , speaker  78 , microphone  82 , and/or other user interfaced devices such as a touch screen device (not shown) to bus  62 , communication adapter  84  for connecting the information handling system to a data processing network  92 , and display adapter  86  for connecting bus  62  to display device  88 . 
     Although the invention has been described with a certain degree of particularity, it should be recognized that elements thereof may be altered by persons skilled in the art without departing from the spirit and scope of the invention. One of the embodiments of the invention can be implemented as sets of instructions resident in the random access memory  64  of one or more computer systems configured generally as described in  FIG. 4 . Until required by the computer system, the set of instructions may be stored in another computer readable memory, for example in a hard disk drive, or in a removable memory such as an optical disk for eventual use in a CD-ROM drive or a floppy disk for eventual use in a floppy disk drive. Further, the set of instructions can be stored in the memory of another computer and transmitted over a local area network or a wide area network, such as the Internet, when desired by the user. One skilled in the art would appreciate that the physical storage of the sets of instructions physically changes the medium upon which it is stored electrically, magnetically, or chemically so that the medium carries computer readable information. The invention is limited only by the following claims and their equivalents.