FIELD OF THE INVENTION  
       [0001]     Embodiments of the present invention generally relate to the field of memory, and, more particularly to a method, apparatus and system for posted write buffer for memory with unidirectional full duplex interface.  
       BACKGROUND OF THE INVENTION  
       [0002]     As the computing power of processors increases, so does the need for faster data transfers with memory devices. In addition to improving memory bandwidth, it is beneficial to improve the efficiency with which memory bandwidth is utilized. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]     The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements, and in which:  
         [0004]      FIG. 1  is a block diagram of an example electronic appliance suitable for implementing a buffer agent, in accordance with one example embodiment of the invention;  
         [0005]      FIG. 2  is a block diagram of an example buffer agent architecture, in accordance with one example embodiment of the invention;  
         [0006]      FIG. 3  is a flow chart of an example method for posted write buffering, in accordance with one example embodiment of the invention; and  
         [0007]      FIG. 4  is a block diagram of an example storage medium comprising content which, when accessed by a device, causes the device to implement one or more aspects of one or more embodiment(s) of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0008]     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that embodiments of the invention can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the invention.  
         [0009]     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.  
         [0010]      FIG. 1  is a block diagram of an example electronic appliance suitable for implementing a buffer agent, in accordance with one example embodiment of the invention. Electronic appliance  100  is intended to represent any of a wide variety of traditional and non-traditional electronic appliances, laptops, desktops, cell phones, wireless communication subscriber units, wireless communication telephony infrastructure elements, personal digital assistants, set-top boxes, or any electric appliance that would benefit from the teachings of the present invention. In accordance with the illustrated example embodiment, electronic appliance  100  may include one or more of processor(s)  102 , memory controller  104 , buffer agent  106 , system memory  108 , posted write buffer  110 , write interface  112 , read interface  114 , input/output controller  116 , network controller  118 , and input/output device(s)  120  coupled as shown in  FIG. 1 . Buffer agent  106 , as described more fully hereinafter, may well be used in electronic appliances of greater or lesser complexity than that depicted in  FIG. 1 . Also, the innovative attributes of buffer agent  106  as described more fully hereinafter may well be embodied in any combination of hardware and software.  
         [0011]     Processor(s)  102  may represent any of a wide variety of control logic including, but not limited to one or more of a microprocessor, a programmable logic device (PLD), programmable logic array (PLA), application specific integrated circuit (ASIC), a microcontroller, and the like, although the present invention is not limited in this respect.  
         [0012]     Memory controller  104  may represent any type of chipset or control logic that interfaces system memory  108  with the other components of electronic appliance  100 . In one embodiment, the connection between processor(s)  102  and memory controller  104  may be referred to as a front-side bus. In another embodiment, memory controller  104  may be referred to as a north bridge.  
         [0013]     Buffer agent  106  may have an architecture as described in greater detail with reference to  FIG. 2 . Buffer agent  106  may also perform one or more methods for buffering memory writes, such as the method described in greater detail with reference to  FIG. 3 . While shown as being part of memory controller  104 , buffer agent  106  may well be part of another component, for example processor(s)  102  or input/output controller  116 , or may be implemented in software or a combination of hardware and software.  
         [0014]     System memory  108  may represent any type of memory device(s) used to store data and instructions that may have been or will be used by processor(s)  102 . Typically, though the invention is not limited in this respect, system memory  108  will consist of dynamic random access memory (DRAM). In one embodiment, system memory  108  may consist of Rambus DRAM (RDRAM). In another embodiment, system memory  108  may consist of double data rate synchronous DRAM (DDRSDRAM). The present invention, however, is not limited to the examples of memory mentioned here.  
         [0015]     Posted write buffer  110  represents a relatively small memory used to temporarily store data before it is retired (written) to its destination address. Posted write buffer  110  may be indexed so that a particular data entry can be retired irrespective of the order in which it was received. In one embodiment, Posted write buffer  110  also stores the address(es) to which the data will eventually be retired. Posted write buffer  110  may contain control logic to, among other things, reset and maintain a buffer pointer, to input data to buffer locations, and to output data to memory devices.  
         [0016]     Write interface  112  represents a unidirectional interface through which data and commands are sent to system memory  108 . In one embodiment write interface  112  is a serial interface. In another embodiment write interface  112  is a parallel interface.  
         [0017]     Read interface  114  represents a unidirectional interface through which data is read from system memory  108 . In one embodiment read interface  114  is a serial interface. In another embodiment read interface  114  is a parallel interface.  
         [0018]     Input/output (I/O) controller  116  may represent any type of chipset or control logic that interfaces I/O device(s)  120  with the other components of electronic appliance  100 . In one embodiment, I/O controller  116  may be referred to as a south bridge. In another embodiment, I/O controller  116  may comply with the Peripheral Component Interconnect (PCI) Express™ Base Specification, Revision 1.0a, PCI Special Interest Group, released Apr. 15, 2003.  
         [0019]     Network controller  118  may represent any type of device that allows electronic appliance  100  to communicate with other electronic appliances or devices. In one embodiment, network controller  118  may comply with a The Institute of Electrical and Electronics Engineers, Inc. (IEEE) 802.11b standard (approved Sep. 16, 1999, supplement to ANSI/IEEE Std 802.11, 1999 Edition). In another embodiment, network controller  118  may be an Ethernet network interface card.  
         [0020]     Input/output (I/O) device(s)  120  may represent any type of device, peripheral or component that provides input to or processes output from electronic appliance  100 .  
         [0021]      FIG. 2  is a block diagram of an example buffer agent architecture, in accordance with one example embodiment of the invention. As shown, buffer agent  106  may include one or more of control logic  202 , memory  204 , controller interface  206 , and buffer engine  208  coupled as shown in  FIG. 2 . In accordance with one aspect of the present invention, to be developed more fully below, buffer agent  106  may include a buffer engine  208  comprising one or more of data services  210 , table services  212 , and/or retire services  214 . It is to be appreciated that, although depicted as a number of disparate functional blocks, one or more of elements  202 - 214  may well be combined into one or more multi-functional blocks. Similarly, buffer engine  208  may well be practiced with fewer functional blocks, i.e., with only table services  212 , without deviating from the spirit and scope of the present invention, and may well be implemented in hardware, software, firmware, or any combination thereof. In this regard, buffer agent  106  in general, and buffer engine  208  in particular, are merely illustrative of one example implementation of one aspect of the present invention. As used herein, buffer agent  106  may well be embodied in hardware, software, firmware and/or any combination thereof.  
         [0022]     Buffer agent  106  may have the ability to send data to a posted write buffer, to maintain a table of the data in the posted write buffer, and to retire data from the posted write buffer to a memory address. In one embodiment, buffer agent  106  may communicate to posted write buffer  110  the buffer location to be used to store the data. In another embodiment, buffer agent  106  and posted write buffer  110  may utilize a shared algorithm to determine which buffer location will be used to store data without requiring the location to be communicated.  
         [0023]     As used herein control logic  202  provides the logical interface between buffer agent  106  and its host electronic appliance  100 . In this regard, control logic  202  may manage one or more aspects of buffer agent  106  to provide a communication interface to electronic appliance  100 , e.g., through memory controller  104 . Control logic  202  may also enable buffer agent  106  to determine if can be written (retired) to a particular memory address or whether a read transaction is temporarily blocking the ability to write to certain memory devices.  
         [0024]     According to one aspect of the present invention, though the claims are not so limited, control logic  202  may selectively invoke the resource(s) of buffer engine  208 . As part of an example method for posted write buffering, as explained in greater detail with reference to  FIG. 3 , control logic  202  may selectively invoke data services  210  that may send data to a posted write buffer. Control logic  202  also may selectively invoke table services  212  or retire services  214 , as explained in greater detail with reference to  FIG. 3 , to maintain a table of the data in the posted write buffer or to retire data from the posted write buffer to a memory address, respectively. As used herein, control logic  202  is intended to represent any of a wide variety of control logic known in the art and, as such, may well be implemented as a microprocessor, a micro-controller, a field-programmable gate array (FPGA), application specific integrated circuit (ASIC), programmable logic device (PLD) and the like. In some implementations, control logic  202  is intended to represent content (e.g., software instructions, etc.), which when executed implements the features of control logic  202  described herein.  
         [0025]     Memory  204  is intended to represent any of a wide variety of memory devices and/or systems known in the art. According to one example implementation, though the claims are not so limited, memory  204  may well include volatile and non-volatile memory elements, possibly random access memory (RAM) and/or read only memory (ROM). Memory  204  may be used to store a table to represent the data stored in posted write buffer  110 , for example.  
         [0026]     Controller interface  206  provides a path through which buffer agent  106  can communicate with memory controller  104 . Buffer agent  106  utilizes this interface to receive data to be written to memory and to send data and commands along write interface  112  to system memory  108 .  
         [0027]     As introduced above, buffer engine  208  may be selectively invoked by control logic  202  to send data to a posted write buffer, to maintain a table of the data in the posted write buffer, or to retire data from the posted write buffer to a memory address. In accordance with the illustrated example implementation of  FIG. 2 , buffer engine  208  is depicted comprising one or more of data services  210 , table services  212  and retire services  214 . Although depicted as a number of disparate elements, those skilled in the art will appreciate that one or more elements  210 - 214  of buffer engine  208  may well be combined without deviating from the scope and spirit of the present invention.  
         [0028]     Data services  210 , as introduced above, may provide buffer agent  106  with the ability to send data to a posted write buffer. In one example embodiment, data services  210  may send the address to which the data will ultimately be retired along with the data to be stored temporarily in posted write buffer  110 . In another embodiment, a data frame sent to posted write buffer  110  may include a bit vector to indicate the buffer entry in which to store the data. Alternatively, the bit vector can be left out if there is a shared algorithm by which table services  212  and posted write buffer  110  know beforehand the buffer entry in which the data will be stored. The data frame could include a byte of data or a series of bytes so as to match the entry size of posted write buffer  110  or the write protocol for system memory  108 .  
         [0029]     As introduced above, table services  212  may provide buffer agent  106  with the ability to maintain a table of the data in the posted write buffer. In one example embodiment, table services  212  may maintain a table in memory  204  that contains the same data as posted write buffer  110 . In another embodiment, the table maintained in memory  204  may contain a subset of the data stored in posted write buffer  110  or may contain the memory addresses associated with the data indexed in posted write buffer  110 . Table services  212  may share an algorithm with posted write buffer  110  to determine in which buffer entry a particular set of data will be stored. In one embodiment, both table services  212  and posted write buffer  110  know the size of posted write buffer  110 , the buffer entry in which to store the first set of data after a reset, and the method for selecting subsequent buffer entries. An example method for selecting subsequent buffer entries would be to utilize the first unused entry.  
         [0030]     Retire services  214 , as introduced above, may provide buffer agent  106  with the ability to retire data from the posted write buffer to a memory address. In one embodiment, retire services  214  may send a column access strobe (CAS) command to a memory address of system memory  108  along with a bit vector corresponding to the data entry in posted write buffer  110  that is to be retired. In another embodiment, retire services  214  may send only the bit vector corresponding to the data entry in posted write buffer  110  that is to be retired, where posted write buffer  110  contains the memory address to which the data is to be retired.  
         [0031]      FIG. 3  is a flow chart of an example method for posted write buffering, in accordance with one example embodiment of the invention. It will be readily apparent to those of ordinary skill in the art that although the following operations may be described as a sequential process, many of the operations may in fact be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged without departing from the spirit of embodiments of the invention.  
         [0032]     According to but one example implementation, method  300  begins with data services  210  being invoked to send ( 302 ) memory write data to posted write buffer  110 . In one example embodiment, the data could be received from network controller  118 . In another embodiment, the data could be provided by processor  102 .  
         [0033]     Next, buffer agent  106  may invoke table services  212  to create ( 304 ) a table entry. In one example embodiment, table services  212  tracks the data sent to posted write buffer  110  and the addresses to which the data will be written.  
         [0034]     Next, control logic  202  may decide ( 306 ) whether data in the posted write buffer can be retired. In one embodiment, a read transaction from a particular memory bank would prevent a write to that memory bank from occurring simultaneously. Based on the address to which the data will be written, control logic  202  may determine whether the data can be retired.  
         [0035]     If the data can not be retired, control logic  202  may selectively invoke send services  210  or retire services  214  to send ( 308 ) or retire other data, respectively. In one example embodiment, send services  210  is selectively invoked to send other data to be temporarily stored in posted write buffer  110  if there is no other data that can be retired. In another embodiment, retire services  214  is selectively invoked to retire other data stored in posted write buffer  110  if there are no unused buffer entries.  
         [0036]     If the data can be retired, control logic  202  may selectively invoke retire services  214  and table services  212  to retire ( 310 ) data and update table entries, respectively. In one embodiment, retire services  214  includes a bit vector corresponding to the data in posted write buffer  110  to be retired as part of a CAS frame that prepares the appropriate memory device to store the data. Table services  212  may clear the entry associated with the data retired so that it may be reused.  
         [0037]      FIG. 4  illustrates a block diagram of an example storage medium comprising content which, when accessed by a device, causes the device to implement one or more embodiment(s) of the invention, for example buffer agent  106  and/or associated method  300 . In this regard, storage medium  400  includes content  402  (e.g., instructions, data, or any combination thereof) which, when executed, causes the appliance to implement one or more aspects of buffer agent  106 , described above.  
         [0038]     The machine-readable (storage) medium  400  may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, or other type of media/machine-readable medium suitable for storing electronic instructions. Moreover, the present invention may also be downloaded as a computer program product, wherein the program may be transferred from a remote computer to a requesting computer by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem, radio or network connection).  
         [0039]     Many of the methods are described in their most basic form but operations can be added to or deleted from any of the methods and information can be added or subtracted from any of the described messages without departing from the basic scope of the present invention. Any number of variations of the inventive concept is anticipated within the scope and spirit of the present invention. In this regard, the particular illustrated example embodiments are not provided to limit the invention but merely to illustrate it. Thus, the scope of the present invention is not to be determined by the specific examples provided above but only by the plain language of the following claims.
In some embodiments, a method, apparatus and system for posted write buffer for memory with unidirectional full duplex interface are presented. In this regard, a buffer agent is introduced to send data to a posted write buffer and to send an independent indication to the memory to write the data to an address. Other embodiments are also disclosed and claimed.