Patent Application
20080005383
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
The illustrative embodiment is a computer-implemented method, apparatus, and computer program product for stalling DMA operations in a host bridge, without stopping MMIO load operations, while migrating data from a source physical page to a destination physical page in a system that executes MMIO load operations using split transactions. According to the illustrative embodiment, the data migration process is restarted when there is the need to process an MMIO load operation while DMA operations are stalled.
The illustrative embodiment provides for a soft stop state and a hard stop state for implementation within a host bridge, such as a PCI host bridge (PHB).
In a first embodiment of the present invention, all DMA operations through a host bridge are suspended during migration of data from a source page to a destination page when a DMA write operation is encountered, regardless of whether or not the DMA write operation attempted to access the source page. When data needs to be migrated from a source physical page to a destination physical page, software sets the soft stop bit within the host bridge. The host bridge enters the soft stop state when the soft stop bit is set and a DMA write operation occurs at the host bridge. While in the soft stop state, the host bridge suspends direct memory access (DMA) traffic from the I/O devices, which are connected to that host bridge, to memory. During the time that the soft stop state is active, the host bridge will continue to process MMIO store traffic. If the host bridge receives an MMIO load operation while the host bridge is in the soft stop state, the soft stop state will be suspended in order to allow the MMIO load operation to be processed. If the soft stop state is suspended in order to allow an MMIO load operation to be processed, the migration process will need to be restarted.
If the migration is able to complete without the soft stop state being suspended, the host bridge will enter the hard stop state so that software can complete the final steps of the migration process, including changing addresses. When the host bridge enters the hard stop state, all DMA and all MMIO traffic, including both MMIO load and load reply operations, through that host bridge is suspended. While the host bridge is in the hard stop state, the software can complete the final steps of the migration process.
The first illustrative embodiment of the present invention describes a soft stop bit, a hard stop bit, and a soft stop fault bit that are included in a host bridge. A host bridge enters the soft stop state when its soft stop bit is set equal to 1 and the host bridge receives a DMA write operation to process. A soft stop fault bit indicates whether the host bridge received an MMIO load operation while the host bridge was in the soft stop state. A host bridge is not in the soft stop state when its soft stop bit is set equal to 0. A host bridge is not in the hard stop state when its hard stop bit is set equal to 0.
A table is described herein that includes multiple entries. The table is referred to as a translation and control table. Each entry in the table associates a particular source physical page with a particular I/O adapter. The entries are referred to as translation and control entries (TCEs). The table is indexed by the I/O bus address of DMA operations.
More specifically, when software needs to migrate data from a source physical page to a destination physical page, the software sets the soft stop bit equal to 1 in all host bridges that might access the source page. The software then flushes any remaining DMA writes from those host bridges by issuing an MMIO load operation to all host bridges that might be using table entries that point to the source page. The software then copies the data from the source page to the destination page.
In each host bridge that might access the source page, the software checks to see if the soft stop fault bit was set equal to 1 during the migration of the data. The soft stop fault bit would have been set equal to 1 had the host bridge received an MMIO load operation while the data was being migrated. If the soft stop fault bit is set equal to 1, the software must restart the migration process.
If the soft stop fault bit is set equal to 0, the hardware sets the hard stop bit equal to 1 when the soft stop bit is read by the software. The hard stop bit is set equal to 1 to cause the host bridge to enter the hard stop state. While the host bridge is in the hard stop state, the value in the table entries that had pointed to the source page are changed to point to the destination page. Once the table entries are changed, the software resets the soft stop bits, hard stop bits, and soft stop fault bits in the affected host bridges to be equal to 0.
In a second embodiment of the present invention, DMA operations through a host bridge are suspended during migration of data from a source physical page to a destination physical page only if a DMA operation attempts to write to the particular source physical page that has the data that is being migrated. If no DMA operation attempts to write to the source page during the migration progress, DMA operations will continue to be processed by the host bridge during the migration of the data.
In the second embodiment, each translation and control entry (TCE) includes a new control bit, referred to herein as the migration-in-progress (MIP) bit. The translation information in a TCE points to a particular physical page. When data in a physical page is to be migrated, the MIP bit in the TCEs that point to that physical page are set equal to 1. When a MIP bit in a TCE is set equal to 0, the data in the page to which the TCE points is not currently being migrated.
Address translation and control logic and DMA control logic are both included in each host bridge. When the address translation and control logic in a host bridge fetches a TCE that has its MIP bit set equal to 1, the DMA control logic sets the host bridge's soft stop bit equal to 1 to cause the host bridge to enter the soft stop state. When the host bridge enters the soft stop state, the host bridge continues to process MMIO store traffic through the host bridge unless the host bridge receives an MMIO load operation to one of its I/O devices.
During the soft stop state, the host bridge suspends DMA operations from the I/O devices, which are connected to that host bridge, to system memory. During the time that the soft stop state is active, the host bridge will continue to process MMIO store operations. If the host bridge receives an MMIO load operation to the I/O device while the host bridge is in the soft stop state, the soft stop state will be suspended in order to allow the MMIO load operation to be processed. In this case the soft stop fault bit will be set to a 1 to signal to the software that the migration process will need to be restarted.
If the migration is able to complete without the soft stop state being suspended, the software will read the soft stop fault bit and it will be a value of 0, in which case the host bridge hardware will set the hard stop bit and the host bridge will enter the hard stop state. When the host bridge enters the hard stop state, all DMA and all MMIO traffic through that host bridge is suspended. While the host bridge is in the hard stop state, the software can complete the final steps of the migration process.
More specifically, when software needs to migrate data from a source page to a destination page, the software sets the MIP bit equal to 1 in all TCEs that point to the source page in all host bridges. The software then flushes any remaining DMA writes from those host bridges by issuing an MMIO load operation to all host bridges that might be using TCEs that point to the source page. The software copies the data from the source page to the destination page. The software then checks each host bridge to see if the host bridge's soft stop fault bit was set equal to 1 during the migration of the data. The soft stop fault bit would have been set equal to 1 had the host bridge received a DMA write operation which targeted the source page and also received an MMIO load operation during the migration. If the soft stop fault bit is set equal to 1, the software must restart the migration process. If the soft stop fault bit is set equal to 0, the hardware sets the hard stop bit equal to 1 when the software reads the soft stop fault bit, which causes the host bridge to enter the hard stop state. While the host bridge is in the hard stop state, the TCEs are then changed to point to the destination page. After the TCEs are changed to point to the destination page, the MIP bits in the TCEs are set equal to 0. Once the TCE table entries are changed, the software resets the soft stop bits, hard stop bits, and soft stop fault bits to be equal to 0.
With reference now to the figures,
I/O bridge 110 includes a table 110a. Translation and control entries (TCEs) are stored in TCE table 110a. Table 110a is an I/O address translation and protection mechanism that provides, on an I/O page basis, the capability to control I/O operations to a physical page from an I/O device.
The TCE entries associate the physical pages of physical memory 160-163 with the I/O bus address pages available on the I/O bus 112 to the I/O adapters 120-124, 148-150. Each entry associates a particular physical page with a particular I/O address page. TCE table 110a is indexed by the I/O bus address of DMA operations. This table is used as an indirect addressing mechanism in much the same way as the virtual address mechanism in the processors provides an indirect addressing mechanism from the software to the physical memory. Such processor virtual address translation mechanisms are well known in the art.
Data processing system 100 is a logically partitioned (LPAR) data processing system; however, it should be understood that the invention is not limited to an LPAR system but can also be implemented in other data processing systems. LPAR data processing system 100 has multiple heterogeneous operating systems (or multiple copies of a single operating system) running simultaneously. Each of these multiple operating systems may have any number of software programs executing within it. Data processing system 100 is logically partitioned such that different PCI input/output adapters (IOAs) 120, 121, 122, 123 and 124, graphics adapter 148 and hard disk adapter 149, or parts thereof, may be assigned to different logical partitions. In this case, graphics adapter 148 provides a connection for a display device (not shown), while hard disk adapter 149 provides a connection to control hard disk 150.
Thus, for example, suppose data processing system 100 is divided into three logical partitions, P1, P2, and P3. Each of PCI IOAs 120-124, graphics adapter 148, hard disk adapter 149, each of host processors 101-104, and memory from local memories 160-163 are assigned to each of the three partitions. In this example, memories 160-163 may take the form of dual in-line memory modules (DIMMs). DIMMs are not normally assigned on a per DIMM basis to partitions. Instead, a partition will get a portion of the overall memory seen by the platform. For example, processor 101, some portion of memory from local memories 160-163, and PCI IOAs 121, 123 and 124 may be assigned to logical partition P1; processors 102-103, some portion of memory from local memories 160-163, and PCI IOAs 120 and 122 may be assigned to partition P2; and processor 104, some portion of memory from local memories 160-163, graphics adapter 148 and hard disk adapter 149 may be assigned to logical partition P3.
Each operating system executing within a logically partitioned data processing system 100 is assigned to a different logical partition. Thus, each operating system executing within data processing system 100 may access only those IOAs that are within its logical partition. For example, one instance of the Advanced Interactive Executive (AIX) operating system may be executing within partition P1, a second instance (copy) of the AIX operating system may be executing within partition P2, and a Linux or OS/400 operating system may be operating within logical partition P3.
Peripheral component interconnect (PCI) host bridges (PHBS) 130, 131, 132 and 133 are connected to I/O bus 112 and provide interfaces to PCI local buses 140, 141, 142 and 143, respectively. PCI buses 140, 141, 142, and 143 preferably conform to the PCI specification. In the embodiments described below, PCI buses 140, 141, 142, and 143 conform to the PCI specification that utilizes split transactions for MMIO operations.
PCI IOAs 120-121 are connected to PCI local bus 140 through I/O fabric 180, which comprises switches and bridges. In a similar manner, PCI IOA 122 is connected to PCI local bus 141 through I/O fabric 181, PCI IOAs 123 and 124 are connected to PCI local bus 142 through I/O fabric 182, and graphics adapter 148 and hard disk adapter 149 are connected to PCI local bus 143 through I/O fabric 183. The I/O fabrics 180-183 provide interfaces to PCI buses 140-143. A typical PCI host bridge will support between four and eight IOAs (for example, expansion slots for add-in connectors). Each PCI IOA 120-124 provides an interface between data processing system 100 and input/output devices such as, for example, other network computers, which are clients to data processing system 100.
PCI host bridge 130 provides an interface for PCI bus 140 to connect to I/O bus 112. This PCI bus also connects PCI host bridge 130 to service processor mailbox interface and ISA bus access pass-through logic 194 and I/O fabric 180. Service processor mailbox interface and ISA bus access pass-through logic 194 forwards PCI accesses destined to the PCI/ISA bridge 193. NVRAM storage 192 is connected to the ISA bus 196. Service processor 135 is coupled to service processor mailbox interface and ISA bus access pass-through logic 194 through its local PCI bus 195. Service processor 135 is also connected to processors 101-104 via a plurality of JTAG/I2C buses 134. JTAG/I2C buses 134 are a combination of JTAG/scan buses (see IEEE 1149.1) and Phillips I2C buses. However, alternatively, JTAG/I2C buses 134 may be replaced by only Phillips I2C buses or only JTAG/scan buses. All SP-ATTN signals of the host processors 101, 102, 103, and 104 are connected together to an interrupt input signal of the service processor. The service processor 135 has its own local memory 191, and has access to the hardware OP-panel 190.
When data processing system 100 is initially powered up, service processor 135 uses the JTAG/I2C buses 134 to interrogate the system (host) processors 101-104, memory controller/cache 108, and I/O bridge 110. At completion of this step, service processor 135 has an inventory and topology understanding of data processing system 100. Service processor 135 also executes Built-In-Self-Tests (BISTs), Basic Assurance Tests (BATs), and memory tests on all elements found by interrogating the host processors 101-104, memory controller/cache 108, and I/O bridge 110. Any error information for failures detected during the BISTs, BATs, and memory tests are gathered and reported by service processor 135.
If a meaningful/valid configuration of system resources is still possible after taking out the elements found to be faulty during the BISTs, BATs, and memory tests, then data processing system 100 is allowed to proceed to load executable code into local (host) memories 160-163. Service processor 135 then releases host processors 101-104 for execution of the code loaded into local memory 160-163. While host processors 101-104 are executing code from respective operating systems within data processing system 100, service processor 135 enters a mode of monitoring and reporting errors. The type of items monitored by service processor 135 include, for example, the cooling fan speed and operation, thermal sensors, power supply regulators, and recoverable and non-recoverable errors reported by processors 101-104, local memories 160-163, and I/O bridge 110.
Service processor 135 is responsible for saving and reporting error information related to all the monitored items in data processing system 100. Service processor 135 also takes action based on the type of errors and defined thresholds. For example, service processor 135 may take note of excessive recoverable errors on a processor's cache memory and decide that this is predictive of a hard failure. Based on this determination, service processor 135 may mark that resource for deconfiguration during the current running session and future Initial Program Loads (IPLs). IPLs are also sometimes referred to as a “boot” or “bootstrap”.
Data processing system 100 may be implemented using various commercially available computer systems. For example, data processing system 100 may be implemented using an IBM eServer iSeries Model 840 system available from International Business Machines Corporation. Such a system may support logical partitioning using an OS/400 operating system, which is also available from International Business Machines Corporation.
Those of ordinary skill in the art will appreciate that the hardware depicted in
Operating systems 202, 204, 206, and 208 are located in partitions 203, 205, 207, and 209. Hypervisor software is an example of software that may be used to implement partition management firmware 210 and is available from International Business Machines Corporation. Firmware is “software” stored in a memory chip that holds its content without electrical power, such as, for example, read-only memory (ROM), programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), and nonvolatile random access memory (nonvolatile RAM).
Additionally, these partitions also include partition firmware 211, 213, 215, and 217. Partition firmware 211, 213, 215, and 217 may be implemented using initial boot strap code, IEEE-1275 Standard Open Firmware, and runtime abstraction software (RTAS), which is available from International Business Machines Corporation.
When partitions 203, 205, 207, and 209 are instantiated, a copy of boot strap code is loaded onto partitions 203, 205, 207, and 209 by partition management firmware 210. Thereafter, control is transferred to the boot strap code with the boot strap code then loading the open firmware and RTAS. The processors associated with or assigned to the partitions are then dispatched to the partition's memory to execute the partition firmware.
Partitioned hardware 230 includes a plurality of processors 232-238, a plurality of system memory units 240-246, a plurality of IOAs 248-262, a storage unit 270, and TCE table 272. Each of the processors 232-238, memory units 240-246, NVRAM storage 298, and IOAs 248-262, or parts thereof, may be assigned to one of multiple partitions within logical partitioned platform 200, each of which corresponds to one of operating systems 202, 204, 206, and 208.
Partition management firmware 210 performs a number of functions and services for partitions 203, 205, 207, and 209 to create and enforce the partitioning of logically partitioned platform 200. Partition management firmware 210 is a firmware implemented virtual machine identical to the underlying hardware. Thus, partition management firmware 210 allows the simultaneous execution of independent OS images 202, 204, 206, and 208 by virtualizing the hardware resources of logical partitioned platform 200.
Service processor 290 may be used to provide various services, such as processing of platform errors in the partitions. These services also may act as a service agent to report errors back to a vendor, such as International Business Machines Corporation. Operations of the different partitions may be controlled through a hardware management console, such as hardware management console 280. Hardware management console 280 is a separate data processing system from which a system administrator may perform various functions including reallocation of resources to different partitions.
In an LPAR environment, it is not permissible for resources or programs in one partition to affect operations in another partition. Furthermore, to be useful, the assignment of resources needs to be fine-grained. For example, it is often not acceptable to assign all IOAs that are attached to a particular PCI host bridge (PHB) to the same partition, as that will restrict configurability of the system, including the ability to dynamically move resources between partitions.
Accordingly, some functionality is needed in the PCI host bridges that connect IOAs to the I/O bus so as to be able to assign resources, such as individual IOAs or parts of IOAs to separate partitions; and, at the same time, prevent the assigned resources from affecting other partitions such as by obtaining access to resources of the other partitions.
Physical memory 302 includes a physical page 304 and physical page 306. In the depicted example, the contents of physical page 304 are going to be migrated to physical page 306. The underlying mechanism that allows this migration to occur is the redirection of the I/O adapter's I/O bus address via the TCE table.
TCE table 300 contains entries that are fetched based on the page address placed on the I/O bus. Contained in the TCE table are entries that translate the I/O bus page address to a new system memory page address. For example, prior to migrating data from source page 304 to destination page 306, TCE 308 points to physical page 304, and TCE 310 points to physical page 304. After migrating data from source page 304 to destination page 306, the addresses in TCE table 300 have been changed so that TCE 308 now points to physical page 306 and TCE 310 now points to physical page 306.
Host bridge 400 communicates with one or more I/O adapters through a secondary bus 410. DMA read and write requests and MMIO load replies flow into host bridge 400 through secondary bus 410. Secondary bus 410 is preferably a PCI bus that implements a PCI specification, such as PCI Express, that utilizes split transactions for MMIO operations.
Host bridge 400 includes address translation and control 412 which fetches TCEs to be used to translate and control DMA operations. Address translation and control 412 is coupled to page migration and control 414.
The soft stop bit is set equal to 1 while the data in a source physical page is being migrated from the source page to a destination physical page. While the soft stop bit is set equal to 1, the soft stop bit signals migration control state machine 500, through link 508, to stall the DMA pipeline if a DMA write operation is received into DMA queue 406. While the pipeline is stalled, host bridge 400 will not process further DMA write traffic that is received through secondary link 410 unless an MMIO load request is being processed from MMIO queues and control 404 (see
Migration control state machine 500 may sense, through link 510, that an MMIO load has been received by host bridge 400 while host bridge 400 is in the soft stop state. In this case, migration control state machine 500 sets the soft stop fault bit equal to 1, which indicates to software that the migration needs to be restarted.
If the soft stop bit is equal to 1 and the soft stop fault bit is equal to 0 when the software reads register 506, page migration and control logic 414 will set the hard stop bit, which signals migration control state machine 500 that migration control state machine 500 should not process any DMA requests even if there is an MMIO load reply signal.
Block 706 illustrates a determination of whether or not there is a stalled DMA write command in the pipeline. If a determination is made that there is not a stalled DMA write command, the process passes to block 714. If a determination is made that there is a stalled DMA write command, the process passes to block 708 which depicts a determination of whether or not the hard stop bit is equal to 1. If a determination is made that the hard stop bit is equal to 1, the process passes back to block 708 until such time that the hard stop bit is equal to 0.
Referring again to block 708, if a determination is made that the hard stop bit is not equal to 1, i.e. it is equal to 0, the process passes to block 710 which depicts setting the soft stop bit fault bit equal to 1. Next, block 712 illustrates processing DMA writes. The process then passes to block 714. Block 714, then, illustrates processing the MMIO load command. The process then terminates as illustrated by block 716.
Next, block 804 depicts a determination of whether or not the soft stop bit is equal to 1 and the soft stop fault bit is equal to 0. If a determination is made that the soft stop bit is equal to 1 and the soft stop fault bit is equal to 0, the process passes to block 806 which illustrates setting the hard stop bit equal to 1. The process then passes to block 808.
Referring again to block 804, if a determination is made that the soft stop bit is equal to 1 and the soft stop fault bit is equal to 0, the process passes to block 808 which depicts returning the current settings of the hard stop bit, soft stop bit, and soft stop fault bit. The process then terminates as illustrated by block 810.
Referring again to block 904, if a determination is made that the hard stop bit is not equal to 1, i.e. it is equal to 0, the process passes to block 906 which illustrates a determination of whether or not the soft stop bit is equal to 1. If a determination is made that the soft stop bit is not equal to 1, the process passes to block 912.
Referring again to block 906, if a determination is made that the soft stop bit is equal to 1, the process passes to block 908 which depicts a determination of whether or not the soft stop fault bit is equal to 1. If a determination is made that the soft stop fault bit is not equal to 1, the process passes back to block 906. If a determination is made that the soft stop fault bit is equal to 1, the process passes to block 910.
Block 910 illustrates a determination of whether or not the received request is a DMA request or an interrupt. If a determination is made that the received request is an interrupt, the process passes back to block 904. If a determination is made that the received request is a DMA request, the process passes to block 912 which depicts processing the DMA normally. The process then terminates as illustrated by block 914.
Referring again to block 1002, if a determination is made that the hard stop bit is equal to 1, the process passes to block 1006 which illustrates a determination of whether or not the MMIO pipeline has stalled because the MMIO queues are full. The MMIO pipeline is stalled if the MMIO queues are full and cannot receive any new additional MMIO requests. If a determination is made that the MMIO pipeline has not stalled, the process passes back to block 1002. If a determination is made that the MMIO pipeline has stalled, the process passes to block 1008 which depicts discarding the MMIO load that is causing the pipeline to stall, setting the appropriate error state, and setting the hard stop bit to be equal to 0. Recovery from the discarded MMIO load is platform dependent. However, recovery will typically include detecting the error, resetting the I/O subsystem, and restarting the outstanding I/O operations. The resetting of the I/O subsystem will include resetting the hard stop bit to be equal to 0. The process then passes back to block 1002.
Next, block 1104 depicts setting the soft stop bit equal to 1, the hard stop bit equal to 0, and the soft stop fault bit equal to 0 in all host bridges that have a TCE that points to the page that is being migrated.
The process then passes to block 1106 which illustrates copying the data from the source page to the destination page. Thereafter, block 1108 illustrates reading the page migration control registers in all host bridges that have mapped the source page. The process of reading these registers causes the hard stop bit to be set equal to 1 if the soft stop bit is equal to 1 and the soft stop fault bit is equal to 0.
Next, block 1110 depicts a determination of whether or not all soft stop fault bits are still equal to 0. If a determination is made that all soft stop fault bits are not still equal to 0, the process passes back to block 1104. Referring again to block 1110, if a determination is made that all soft stop fault bits are still equal to 0, the process passes to block 1112 which illustrates setting all affected TCEs to point to the destination page. Next, block 1114 depicts setting all soft stop, hard stop, and soft stop fault bits equal to 0 in all host bridges. The process then terminates as illustrated by block 1116.
According to a second illustrative embodiment of the present invention, a new control bit is added to each translation and control entry in the TCE table. This bit is referred to herein as a migration-in-progress (MIP) bit. The value of the MIP bit in a TCE indicates whether or not the data in the physical page to which the TCE points is currently being migrated. When the MIP bit is set equal to 1, the data is currently being migrated. When the MIP bit is set equal to 0, the data is not currently being migrated.
Block 1306, then, illustrates a determination of whether or not this is a DMA write and whether the migration-in-progress (MIP) bit is equal to 1. If a determination is made that this is not a DMA write and the migration-in-progress (MIP) bit is equal to 1, the process terminates as depicted by block 1310. Referring again to block 1306, if a determination is made that this is a DMA write and the migration-in-progress (MIP) bit is equal to 1, the process passes to block 1308 which illustrates setting the soft stop bit equal to 1. The process then terminates as depicted by block 1310.
Next, block 1404 depicts issuing a memory mapped input/output (MMIO) load request to each host bridge that has the source page mapped. This MMIO load will cause any hardware invalidations of the TCEs to get to the host bridge prior to the MMIO load reply being returned to the processor, and will make sure that all writes to the TCE prior to its invalidation have been flushed to memory.
The process then passes to block 1406 which illustrates copying the data from the source page to the destination page. Next, block 1408 depicts setting the soft stop bit equal to 1 in all host bridges that might have TCEs that point to the source page. Thereafter, block 1410 illustrates reading the page migration control registers in all host bridges that have mapped the source page. The process of reading these registers causes the hard stop bit to be set equal to 1 if the soft stop bit and the soft stop fault bits are equal to 0.
Next, block 1412 depicts a determination of whether or not all soft stop fault bits are still equal to 0. If a determination is made that not all soft stop fault bits are still equal to 0, the process passes to block 1414 which illustrates setting the soft stop bit equal to 0, the hard stop bit equal to 0, and the soft stop bit equal to 0 in all host bridges. The process then passes back to block 1404.
Referring again to block 1412, if a determination is made that all soft stop fault bits are still equal to 0, the process passes to block 1416 which depicts setting all affected TCEs to point to the destination page. All migration-in-progress (MIP) bits are then set equal to 0 in those TCEs. Thereafter, block 1418 illustrates setting the soft stop bit equal to 0, the hard stop bit equal to 0, the soft stop bit equal to 0, and the soft stop fault bit equal to 0 in all host bridges. The process then terminates as depicted by block 1420.
The invention can take the form of an entirely hardware embodiment or an embodiment containing both hardware and software elements. In a preferred embodiment, the invention is implemented in hardware and software, which includes but is not limited to firmware, resident software, microcode, etc.
Furthermore, the invention can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any tangible apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.
A data processing system suitable for storing and/or executing program code will include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.
Input/output or I/O devices (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled to the system either directly or through intervening I/O controllers.
Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem and Ethernet cards are just a few of the currently available types of network adapters.
The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
