Abstract:
Methods and apparatus are provided for use in testing a memory ( 230 ) coupled to a processing node ( 214 ). A background scrubber ( 316 ) in the processing node ( 214 ) is initialized to perform a test of the memory ( 230 ). A status of the background scrubber ( 316 ) is checked in which the status indicates whether an error occurred during the test. A predetermined action is taken in response to the status indicating that the error occurred during the test.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     Related subject matter is found in a copending U.S. patent application, application Ser. No. 10/763,009, filed Jan. 21, 2004, entitled “MEMORY CHECK ARCHITECTURE AND METHOD FOR A MULTIPROCESSOR COMPUTER SYSTEM”, invented by Oswin Housty and assigned to the Assignee hereof. 
     TECHNICAL FIELD 
     The present invention generally relates to data processing systems, and more particularly relates to data processing systems that perform memory testing such as after system startup. 
     BACKGROUND 
     A computer system is generally defined in terms of three basic system elements: a central processing unit (CPU), memory, and input/output (I/O) peripheral devices. A typical computer system works with a computer program known as an operating system (OS). The OS is a program that manages all other programs in a computer, the user interface, the interface with peripheral devices, memory allocation, and so forth. Each OS is written for a variety of system configurations such as variable physical memory size, various numbers of peripherals connected to the system, etc. and thus it can remain ignorant of the actual system configuration. 
     On the other hand the basic input/output system (BIOS) is a computer program that uses the actual system configuration to manage data flow between the OS and attached memory and I/O peripherals. The BIOS can translate OS requests into concrete actions that the CPU can take in response. The BIOS is usually stored on a nonvolatile memory device such as a read-only memory (ROM) and may be programmed for the particular system configuration. 
     The BIOS also manages operation of the computer system after startup and before control is passed to the OS. The BIOS typically performs a memory check after power-on to determine whether the memory physically present in the system is operational and can be used by the OS, and takes corrective action if it finds any bad memory blocks. After completing the memory check and other startup tasks the BIOS passes control to the OS but thereafter is periodically called by the OS to perform system specific I/O functions. 
     Early personal computers (PCs) based on the IBM architecture and the DOS operating system showed the progress of the memory check on the screen. For early PCs with their relatively small amounts of memory (by today&#39;s standards) the memory check was a minor annoyance, and DOS displayed the progress of the memory check on the computer screen. As time went on, microprocessors and computer memories became faster. At the same time integrated circuit memories became cheap and new memory-intensive software programs were developed. Thus the length of the memory check at startup has remained a problem. 
     Furthermore certain computer applications such as servers are memory intensive. Thus the amount of time required for the memory check would delay normal system operation so long as to be a nuisance to users. One solution to this problem is to merely sample test a certain portion of the memory at startup. While this allows some memory testing to take place at startup before control is passed to the operating system, the amount of memory coverage at startup using such a scheme is low. 
     Thus it would be desirable to increase the amount of memory that can be tested at system startup without causing an annoyingly long delay, or alternatively to shorten the time required by the memory check to allow more memory to be tested in a given period of time. These and other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     BRIEF SUMMARY 
     A method is provided for use in testing a memory coupled to a processing node. A background scrubber in the processing node is initialized to perform a test of the memory. A status of the background scrubber is checked in which the status indicates whether an error occurred during the test. A predetermined action is taken in response to the status indicating that the error occurred during the test. 
     In another form a method is provided for use in a multiprocessing system having a plurality of processing nodes each including a memory. A background scrubber in each of the plurality of processing nodes is initialized to perform a test of the memory. A status of the background scrubber in each of the plurality of processing nodes is checked, in which the status indicates whether an error occurred during the test of the memory. A predetermined corrective action is taken in each of the plurality of processing nodes in which the status indicates that at least one error occurred during the test of the memory. 
     In another form a method is provided of testing a memory coupled to a processing node. A test of a plurality of locations in the memory is performed. Whether an error occurred during the test is determined. A predetermined corrective action is taken in response to at least one non-correctable error. A different action is taken in response to at least one correctable error. 
     In yet another form a basic input/output system (BIOS) memory adapted to be coupled to a boot strap processor (BSP) includes first, second, third, and fourth sets of instructions. The first set of instructions is executable by the BSP to initialize a background scrubber in a processor node to test a predetermined portion of a memory. The second set of instructions is executable by the BSP to determine when the background scrubber has tested the predetermined portion of the memory. The third set of instructions is executable by the BSP to determine whether any errors occurred when the background scrubber tested the predetermined portion of the memory. The fourth set of instructions is executable by the BSP to take a predetermined corrective action in response to the third set of instructions determining that at least one error occurred. 
     In still another form a method of testing a memory is provided for a computer system having the memory. A plurality of memory locations of the memory are tested. Whether an error occurred during testing is determined. If the error occurred, whether the error is correctable or non-correctable is determined. The memory is reconfigured to exclude a memory location if the error is non-correctable. A predetermined action is taken if the error is correctable. 
     SUMMARY 
     A method is provided for use in testing a memory coupled to a processing node. A background scrubber in the processing node is initialized to perform a test of the memory. A status of the background scrubber is checked in which the status indicates whether an error occurred during the test. A predetermined action is taken in response to the status indicating that the error occurred during the test. 
     In another form a method is provided for use in a multiprocessing system having a plurality of processing nodes each including a memory. A background scrubber in each of the plurality of processing nodes is initialized to perform a test of the memory. A status of the background scrubber in each of the plurality of processing nodes is checked, in which the status indicates whether an error occurred during the test of the memory. A predetermined corrective action is taken in each of the plurality of processing nodes in which the status indicates that at least one error occurred during the test of the memory. 
     In another form a method is provided of testing a memory coupled to a processing node. A test of a plurality of locations in the memory is performed. Whether an error occurred during the test is determined. A predetermined corrective action is taken in response to at least one non-correctable error. A different action is taken in response to at least one correctable error. 
     In yet another form a basic input/output system (BIOS) memory adapted to be coupled to a boot strap processor (BSP) includes first, second, third, and fourth sets of instructions. The first set of instructions is executable by the BSP to initialize a background scrubber in a processor node to test a predetermined portion of a memory. The second set of instructions is executable by the BSP to determine when the background scrubber has tested the predetermined portion of the memory. The third set of instructions is executable by the BSP to determine whether any errors occurred when the background scrubber tested the predetermined portion of the memory. The fourth set of instructions is executable by the BSP to take a predetermined corrective action in response to the third set of instructions determining that at least one error occurred. 
     In still another form a method of testing a memory is provided for a computer system having the memory. A plurality of memory locations of the memory are tested. Whether an error occurred during testing is determined. If the error occurred, whether the error is correctable or non-correctable is determined. The memory is reconfigured to exclude a memory location if the error is non-correctable. A predetermined action is taken if the error is correctable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  illustrates a block diagram of a personal computer (PC) system known in the prior art; 
         FIG. 2  illustrates a block diagram of a multiprocessor computer system according to the present invention; 
         FIG. 3  illustrates in block diagram form a portion of the computer system of  FIG. 2  having a bad memory element; 
         FIG. 4  illustrates a flow chart of a memory check algorithm according to the present invention; 
         FIG. 5  illustrates a flow chart of the waiting step of  FIG. 4 ; 
         FIG. 6  is a timing diagram illustrating the operation of the BIOS service processor of  FIG. 2  after power on; and 
         FIG. 7  is a timing diagram illustrating an alternative form of a memory check algorithm according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
       FIG. 1  illustrates a block diagram of a computer system  100  known in the prior art. Generally computer system  100  is a conventional personal computer (PC) system having an architecture adapted from the PC architecture first designed by the International Business Machines Corporation. Computer system  100  includes a high-performance central processing unit (CPU)  110  that executes instructions of the so-called x86 instruction set such as the microprocessor sold under the Athlon trademark available from Advanced Micro Devices of Sunnyvale, Calif. The x86 instruction set is based on the instruction set of the 8086 microprocessor first manufactured by Intel Corporation of Santa Clara, Calif. CPU  110  generally interfaces to external devices over a system bus  132  by which it is coupled to a system controller  120 , conventionally referred to as a “Northbridge”. Northbridge  120  offloads CPU  110  of the task of communicating with high performance system resources which may have different bus structures. One of these devices is main memory  134  in the form of synchronous dynamic random access memory (SDRAM) or double data rate (DDR) SDRAM over a dedicated memory bus  128 . Another one of these devices is an advanced graphics processor (AGP)  132  over an AGP bus  126 . 
     Northbridge  120  is also connected to a lower performance peripheral component interconnect (PCI) bus  122  to which several other devices, including a local area network (LAN) controller  136  and a small computer system interface (SCSI) controller  138 , are connected. Also connected to PCI bus  122  is a peripheral bus controller  140 , conventionally referred to as a “Southbridge”, for coupling to even lower performance devices. Southbridge  122  has various dedicated buses including a modem/audio bus  142 , a Low Pin Count (LPC) bus  144 , a universal serial bus (USB)  146 , and a dual Enhanced Integrated Drive Electronics (EIDE) bus  148 . One of the devices coupled to LPC bus  144  is a basic input/output system (BIOS) read only memory (ROM) chip  150 . Southbridge  140  is connected to a thermal monitor  114  which is connected to CPU  110  and allows Southbridge  140  to perform power management functions if CPU  110  exceeds a certain temperature during operation. Southbridge  140  has a bidirectional connection to CPU  110  by which CPU  110  programs it for operation. 
     In addition, Southbridge  140  has a bus known as a system management (SM) bus labeled “SM BUS”  160  by which it is connected to memory  134 . SM BUS  160  is the mechanism by which CPU  110 , under the control of the BIOS program stored in BIOS ROM  150 , is able to perform memory tests on memory  134  at startup. This conventional memory test may be performed as follows. After CPU  110  comes up out of reset, it fetches a reset vector pointing to a location in BIOS ROM  150  containing the startup program sequence. One of the items performed in the startup program sequence is to determine the configuration of memory  134 . The BIOS directs Southbridge  140  to poll memory  134  over SM bus  160  to determine how much memory is installed. After determining the memory configuration, the BIOS performs a memory check through Northbridge  120 . For example, the BIOS may cause CPU  110  to write a predefined test pattern (e.g., $55) to all memory locations, and subsequently read the memory locations to determine whether the test pattern was correctly stored. Later an opposite test pattern may be applied (e.g., $AA) to all memory locations and read back to determine whether each memory cell may assume either logic state. Any bad memory element is noted and used to configure Northbridge  120 , and in this way, bad memory may be mapped out of the system. 
     While this type of test can be efficiently performed on PCs which have a relatively small amount of memory, it becomes more difficult as the size of memory becomes larger. Furthermore new computers based on multiprocessor architectures may have their memory distributed among many system nodes, but configure the system using a BIOS program connected to a single node. In such a system this simple local memory test and reconfiguration will no longer suffice. 
     An alternate way of performing a memory test in a multiprocessor computer system can be better understood with reference to  FIG. 2 , which illustrates a block diagram of a multiprocessor computer system  200  according to the present invention. Computer system  200  includes generally eight processor nodes  210 – 217  connected in an array or fabric in which each node is connected to one or more adjacent nodes. For example, system  200  is an eight-processor system in which node  210  labeled “ 0 ” is connected to adjacent nodes  1  and  7 ; node  211  labeled “ 1 ” is connected to adjacent nodes  0 ,  2 , and  5 ; and so on. Each node used in system  200  has three available link controllers which are connected to either adjacent processor nodes or to I/O devices. Since nodes  0 ,  2 ,  4  and  6  use only two of their available three link controllers to connect to adjacent processor nodes, they have an additional link controller available for connection to I/O devices. 
     Each node in system  200  also has the capability to connect to local memory that will be directly accessible to it and indirectly accessible to all other processor nodes. In system  200 , for example, node  210  is connected to a 256 megabyte (MB) DRAM  220 , node  214  is connected to a 512 MB DRAM memory  230 , and node  217  is connected to a 256 MB DRAM memory  240 . However many other memory configurations are possible using various array configurations and memory may in fact be present on all of the nodes. 
     While the physical memory in system  200  is distributed among the nodes, all the memory is visible to every node. Thus the array is configured by programming respective nodes with configuration information. This configuration information can be used to form a system address map, which is a table of all memory and memory-mapped I/O devices in the system, and a node address map. If the processor in node  210  initiates an access to a particular physical address, the memory controller in node  210  will determine whether the physical address corresponds to a location in local memory  220  or in remote memory. If the physical address is in local memory, the memory controller in node  210  performs the access to DRAM  220 . If the physical address is in remote memory, the memory controller in node  210  determines the node number corresponding to the physical address and issues a request packet addressed to that node. The request packet eventually reaches the memory controller in the accessed node after it “hops” between the nodes over the array using the appropriate link controllers. 
     In order to determine the memory configuration in this multiprocessor system, one of the nodes is selected to be the boot strap processor (BSP). In system  200 , node  210  is the BSP (referred to hereinafter as BSP  210 ), and it includes a link controller connected to an I/O device in the form of a Southbridge  250 , which in turn is connected to a BIOS ROM  260 . Note that as used herein “BIOS” refers to either the software stored in BIOS ROM  260  or the device storing the software, as the context dictates. Note that the BIOS can be stored in any of a variety of known storage media, including a ROM, an erasable programmable ROM (EPROM), and electrically erasable programmable ROM (EEPROM), a flash EEPROM, and the like. 
     The selection of the node to be the BSP occurs as follows. On power up, the processor in each node contains startup microcode that sends packets on all three of its link controllers to determine what kind of device the respective link controller is connected to. For example, the first link controller on node  210  detects that it is connected to a processor (node  211 ), the second link controller detects that it is connected to a processor (node  217 ), and the third link controller detects that it is connected to a Southbridge (Southbridge  250 ). In response to detecting that its third link controller is connected to a Southbridge, node  210  becomes the BSP and accesses BIOS  260  to begin the startup sequence for the system. 
     Southbridge  250  is connected to all the memory devices in system  200  over an SM BUS  270 . Thus at startup the BIOS executing on BSP  210  uses SM BUS  270  to determine the amount and node location of memory devices in the system and to communicate the initial configuration to the processor array. The BIOS communicates this information to the processor array by programming the memory controllers and DRAM controllers in respective nodes with the configuration information. After the initial configuration has been determined, the BIOS performs a memory check, determines where any bad memory elements are located, and subsequently maps them out. 
     To explain how BSP  210  configures and tests the memory, reference is now made to  FIG. 3 , which illustrates in block diagram form a portion of computer system  200  of  FIG. 2  having a bad memory element. This portion includes node  214  and its associated local memory  230  both shown in greater detail. Node  214  includes a data processor in the form of a single-chip microprocessor  300  and an input/output (I/O) device  340 . Microprocessor  300  includes generally a central processing unit (CPU)  302 , a memory controller labeled “MCT”  304 , a crossbar switch labeled “XBAR”  306 , three link controllers  308 ,  310 , and  312  each labeled “HT” for HyperTransport, described more fully below, and a DRAM controller (DCT)  314 . 
     CPU  302  is a processor adapted to execute instructions of the x86 instruction set. CPU  302  however includes many sophisticated functions for high-performance execution of x86 programs including pipelining and superscalar design. 
     Memory controller  304  is the mechanism for data transfer between CPU  302  and both its local memory and remote memory distributed throughout the rest of the system. Memory controller  304  offloads the task of initiating and terminating memory accesses from CPU  302  and thus functions as an integrated Northbridge. It includes internal queues to allow efficient use of the external bus to the local memory. It also includes memory maps to determine whether an address of a memory access is intended for local memory or for remote memory, in which case it initiates a request packet to another node connected to node  214  via HT link controller  308  or  310 . 
     Memory controller  304  includes a background scrubber  316 . Background scrubber  316  operates with a machine check architecture (MCA) block (not shown in  FIG. 3 ) to provide a hardware mechanism to detect and report a variety of hardware (or machine) errors when reading and writing data, probing the caches, and during cache line fill and writeback operations. Software can enable microprocessor  300  to report machine check errors through the so-called machine check exception. The error conditions are logged in a set of model-specific registers (MSRs) that can be used by system software to determine the possible source of a hardware problem. 
     In particular background scrubber  316  is associated with memory  230  and is a hardware circuit that operates in the background, independent of CPU  302 . In a background mode, it periodically wakes up during idle periods to read portions of memory  230  to look for errors using an error correcting code (ECC) mechanism built in to the Northbridge portion of microprocessor  300 . The ECC mechanism allows certain memory errors to be detected and corrected, and other more serious memory errors to be detected. The ECC mechanism calculates and stores a Reed-Solomon code that describes the bit sequence of a unit of data. For example a 64-bit word requires seven extra bits to store this code and the MCA uses an eight-bit byte to store the ECC. Then when the data is next read, the stored ECC is compared to the calculated ECC. This mechanism allows single-bit errors (“correctable errors”) to be detected and corrected, and multiple bit errors (“non-correctable errors”) to be detected but not corrected. If background scrubber  316  finds a single-bit ECC error, it is able to correct the error and rewrite the correct data back to memory  230 . Thus it corrects the error before the memory line is read during normal operation, and thus saves the additional time it would take to fix single-bit ECC errors when they are encountered during normal operation. 
     Background scrubber  316  also has a mode known as redirect mode. In redirect mode, background scrubber  316  detects ECC errors while a requesting device, such as CPU  302 , accesses memory  230  during normal operation. Background scrubber  316  corrects correctable ECC errors as data is passed to the requesting device. Redirect mode and background scrubbing may both be active at the same time. Thus correctable errors “redirect” background scrubber  316  from the next address to be scrubbed in background mode to the memory location accessed by the requesting device that caused the error. Background scrubber  316  then rewrites the correct data back to memory  230  and resumes background operation, proceeding to the next address to be scrubbed after the end of the programmed interval. As will be described further below, the BIOS advantageously uses these features of background scrubber  316  to help it perform the memory check more efficiently. 
     XBAR  306  is a switching/multiplexing circuit designed to couple together the buses internal to microprocessor  300 . 
     HT link controllers  308 ,  310 , and  312  are coupled to devices external to microprocessor  300  over corresponding input and output channels. Each of HT link controllers  308 ,  310 , and  312  substantially complies with the physical interface specified in the HyperTransport™ I/O Link Specification, Revision 1.03, © 2001 HyperTransport Technology Consortium. In node  214  HT link controllers  308  and  310  function as coherent links that communicate with nodes  213  and  215  of  FIG. 2 , respectively, using a special coherent form of HyperTransport. HT link controller  312  functions as a host bridge that communicates with I/O device  340  using the non-coherent form of HyperTransport. Details of the HyperTransport protocol are not relevant to understanding the present invention and will not be discussed further. 
     I/O device  340  is an input/output device that, for example, implements the local area network communication protocol standardized by the Institute of Electrical and Electronics Engineers (IEEE) under the auspices of the IEEE 802.3 committee, commonly referred to as “Ethernet”. However other types of I/O functions are possible as well. 
     Local memory  230  includes four dual in-line memory modules (DIMMs)  350 – 353 . DIMMs  350 – 353  are banks of dynamic random access memories (DRAMs) and interface to microprocessor  300  using a conventional bus interface. For example, the DRAMs in DIMMs  350 – 353  comply with the JEDEC Double Data Rate (DDR) SDRAM Specification, Standard JESD79, Release 2, May 2002. In order to efficiently interface to multiple banks of memory using DDR timing specifications, microprocessor  300  includes DRAM controller  314  to operate the interface between memory controller  304  and DIMMs  350 – 353 . In addition to generating standard synchronous address, data, and control signals as specified in JESD79, DRAM controller  314  also includes memory region programming and comparison logic to generate unique chip select signals to activate selected ones of DIMMs  350 – 353 . As shown in  FIG. 3 , DRAM controller  314  outputs chip select signals labeled “CS 0 ”, “CS 1 ”, “CS 2 ”, and “CS 3 ” to DIMMs  350 – 353 , respectively. Note that these chip select signals are designated logically but the physical chip select signals are conventionally active low signals. 
     The operation of system  200  in the presence of a bad memory element will now be described by assuming DIMM  352  is bad, i.e., one or more storage locations in DIMM  352  are or become defective causing at least one memory element in DIMM  352  to fail the BIOS memory test. System  200  provides a way for the BIOS to detect the DIMM with the bad memory element using background scrubber  316 , take a corrective action such as mapping it out of the system, and continue operating, as will be described further below. 
       FIG. 4  illustrates a flow chart of a memory check routine  400  according to the present invention. Routine  400  may take various forms such as a subroutine called by the BIOS or a portion of the main BIOS routine. In general each step corresponds to one or more software instructions executable by the CPU in BSP  210 . Routine  400  may be coded by any of a variety of known programming techniques such as C++ language programming, assembly language programming, direct machine language coding, etc. 
     The algorithm begins at step  402  at which time BIOS  260  calls or begins processing routine  400 . At step  404  routine  400  initializes background scrubber  316 . Around this time the BIOS also initializes the overall machine check architecture (MCA) system. Routine  400  initializes background scrubber  316  by programming a starting address (the base address of memory  230 ), a limit address (the highest address in memory  230 ), and an interval value (the shortest interval between tests of successive memory locations), and starting background scrubber  316 . Thus step  404  performs any initialization tasks required to allow background scrubber  316  to test memory  230  independently of BIOS  260  and CPU  302 . BIOS  260  is free to perform other initialization tasks while background scrubber  316  proceeds with the memory test. 
     Next at step  406 , routine  400  waits until background scrubber  316  has completed one full testing cycle of memory  230 . This full testing cycle may not include testing all locations if background scrubber  316  has been programmed to sample test memory  230 . Advantageously during step  406  BIOS  260  is able to perform other power on self test activities that do not interfere with background scrubber  316  (such as operations that use the bus between DRAM controller  314  and memory  230 ). A method by which routine  400  efficiently determines whether background scrubber  316  has completed one full cycle of memory  230  is better understood with respect to  FIG. 5 , which illustrates a flow chart of step  406  of  FIG. 4 . After starting at step  502 , an index parameter N is first set to zero, and a parameter known as the current scrub address and designated “AN” is read by BSP  210 . Scrubber  316  maintains a copy of the current scrub address in an internal memory-mapped register. Next at step  506  the next current scrub address designated “AN+1” is read. Step  508  determines whether the next current scrub address AN+1 is less than the previous current scrub address AN (AN+1&lt;AN). This condition indicates that background scrubber  316  has incremented the current address pointer past the limit of memory  230  and wrapped around to the beginning. If not, at step  510  the index N is incremented and flow returns to step  506 . If AN+1&lt;AN, routine  500  determines that all memory locations have been tested and returns to routine  400 . This method has the advantage that it provides a simple way of determining when background scrubber  316  has incremented the addresses past the end of the memory space occupied by memory  230 . Note that this method does not require that background scrubber  316  test all locations, only that after initialization background scrubber  316  tests memory locations in ascending order and wraps its address after it has reached the limit address. 
     In an alternative implementation having the same advantage of routine  406 , background scrubber  316  could successively decrement (instead of increment) the scrub address during operation. In this case background scrubber  316  would be initialized at step  404  by setting the starting address to the highest address and the limit address to the lowest address. Then step  406  could be realized by altering step  508  to determine whether AN+1&gt;AN. 
     Returning now to  FIG. 4 , once BIOS  260  has determined that memory  230  has been fully tested, it checks the status of background scrubber  316  for errors at step  408 . BIOS  260  performs step  408  by reading a status register in background scrubber  316 . Decision box  410  then changes the flow based on whether any errors occurred. If the status register indicates that no errors occurred, then the memory test is complete and the flow returns to the remaining POST functions at step  418 . If the status register indicates that at least one error occurred, then BIOS  260  next determines whether the error was a correctable error at step  412 . 
     A correctable error status may indicate that the error was marginal and memory  352  is still usable, or that it was caused by a random electrical impulse that doesn&#39;t require correction. On the other hand an uncorrectable error is much more serious and usually indicates that a portion of memory  230 , such as DIMM  352 , is defective. BIOS  260  takes different actions depending upon the type error. If the error is uncorrectable, BIOS  260  takes a corrective action at step  416  since operating with defective memory will result in incorrect functioning of programs. In system  200  this corrective action takes the form of mapping the bad memory element out of the system and reporting the error to the user. Another example would be to alert the user to the error and shut down the computer. If the error is correctable, BIOS  260  takes another, different action at step  414 . This other action may be doing nothing, reporting the error to the user but continuing to operate using the memory element that caused the error, retesting the memory and only mapping the memory element out on a subsequent failure, etc. BIOS  260  discriminates among the types of errors and takes different actions appropriate to the type of error. 
     The memory check architecture described above can be used to check significantly larger amounts of memory in a given amount of time through the use of background scrubber  316  available on processing node  214 , or conversely allows the power on self test to complete in a much shorter amount of time and thus be less annoying to the user. 
     This advantage of the memory check architecture is multiplied in multiprocessor systems in which memory is resident on multiple nodes but only one of the processing nodes is selected to be the BSP. For example with respect to system  200  of  FIG. 2 , node  210  is selected to be the BSP. Node  210  advantageously initializes background scrubbers in each of processor nodes  210 ,  214 , and  217  during the memory test. Thus background scrubber hardware on all three processor nodes acts in parallel to efficiently test memories  220 ,  230 , and  240 . If the memory is evenly distributed on M nodes, then the memory check architecture can reduce memory test time by a factor of about 1/M. 
       FIG. 6  is a timing diagram  600  illustrating the overall operation of the BIOS running on BSP  210  of  FIG. 2  after power on.  FIG. 6  depicts time in the horizontal direction as flowing from left to right with various BIOS tasks depicted along the time axis. Note that the BIOS operations relevant to understanding the present invention are described but the BIOS actually performs many other startup tasks that are conventional and well understood in the art and that will not be described further. Each of the tasks illustrated in  FIG. 6  is performed using appropriate sets of instructions, executable by BSP  210 , coded by any of a variety of known programming techniques such as C++ language programming, assembly language programming, direct machine language coding, etc. 
     BSP  210  performs many initialization tasks after system startup, which can be divided generally into a system initialization portion  610  including a power on task  612  and a power-on self test (POST)  620 . During POST  620 , BSP  210  performs an HT map task  622  by detecting the presence and interconnection of the installed processor nodes. The HT map takes the form of a routing table that the BIOS provides to all nodes, and in this way the BIOS configures the HT fabric. 
     The BIOS subsequently performs a memory configuration task  624  by using SM bus  270  to detect the presence of memory and I/O devices and to construct a system address map, as described more fully below. At this point the system address map will contain bad memory elements, such as single bytes, words or whole areas of blocks, if any are present in system  200 . Memory configuration task  624  also configures the base and limit addresses of chip selects used in the DRAM controller of each node, and programs the appropriate registers in each microprocessor. The CS region information is thus distributed among the nodes of the system. 
     The BIOS then performs an MCA initialization task  626  which initializes the MCA block by programming the registers of the MCA system. MCA initialization task  626  also initializes background scrubber  316 , to allow background scrubber  316  to operate independently of BIOS intervention. Later BIOS  260  performs an MCA status sampling task  628  (corresponding to step  408  in  FIG. 4 ) that allows it to determine whether any errors have occurred. As noted above, BIOS  260  may take different actions depending on the type of error (correctable or non-correctable). The BIOS performs additional tasks after MCA status sampling task  628 , and if the memory test has passed or only reported correctable errors, it transfers control to an operating system (such as the operating systems sold under the trademarks DOS and Windows, the Linux operating system, and the like) that operates during portion  630 . 
     If BSP  210  detects a bad physical address, such as an address for which one or more non-correctable errors occurred, it maps the bad address out of the system, and re-runs POST  620 . 
     Another approach is shown in  FIG. 7 , which is a timing diagram  700  illustrating an alternative form of a memory check algorithm according to the present invention. This alternative memory check algorithm is similar to that illustrated in  FIG. 6  except a different POST  720  replaces POST  620 . POST  720  includes HT map task  622  and memory configuration task  624  as in  FIG. 6 . However POST  720  operates without a background scrubber, and MCA initialization task  726  only initializes other portions of the MCA that may be implemented, such as enabling the ECC mechanism. Then the BIOS programs CPU  302  or BSP  210  to perform the memory check directly in memory test  727 . At the end of memory test  727  there is an MCA status sampling step  728  to check for correctable or non-correctable errors and take appropriate actions in response. 
     This alternative form of the memory check represents an “MCA assist” feature, in which the background scrubber is not used and the CPU or the BSP performs the memory test directly but uses the built-in ECC error detection feature. In this embodiment the CPU or BSP is able to discriminate between correctable errors and non-correctable errors and take different actions based on the type of error. It is also useful for microprocessors that do not implement the full background scrubber mechanism but still use ECCs. 
     Thus a computer system has been described that greatly improves the efficiency of the memory check task. In one form the BIOS is able to start a background scrubber in one or more processor nodes to perform a memory test in parallel with other startup activity. The improved efficiency is multiplied in multiprocessor systems in which memory is distributed among multiple processor nodes but the BIOS executes on a single processor node. The BIOS is also able to take advantage of a built-in ECC mechanism to discriminate between correctable errors and non-correctable errors, and to take different actions based on the type of error. This latter feature is applicable even in systems without a background scrubber in which the CPU or BSP actually performs the memory test. In all of these embodiments, the efficiency of the memory check is improved, resulting in better efficiency and less annoyance to the user at startup. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.