Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
2000-12-07
2004-02-17
Iqbal, Nadeem (Department: 2184)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C714S006130, C714S021000
Reexamination Certificate
active
06694451
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to data storage in computer systems. More particularly, the present invention relates to the validation of data that has been stored in random access memory during periods when the data is susceptible of becoming corrupted, or in mission critical computer systems where tolerance for error is low.
2. Background of the Invention
Almost all computer systems include a processor and a system memory. The system memory functions as the working memory of the computer system, where data is stored that has been or will be used by the processor and other system components. The system memory typically includes banks of dynamic random access memory (DRAM) circuits. According to normal convention, a memory controller interfaces the processor to a memory bus that connects electrically to the DRAM circuits. The system memory provides storage for a large number of instructions and/or a large amount of data for use by the processor, providing faster access to the instructions and/or data than would otherwise be achieved if the processor were forced to retrieve data from a disk or drive.
Because system memory typically is constructed of dynamic random access memory circuits, the contents of the memory are volatile. To preserve the integrity of the data stored in system memory, a periodic refresh signal must be sent to each memory cell to refresh the voltage levels of each cell, where the data is stored. Failure to timely refresh the memory cells of system memory causes the data to be lost. Thus, when power is turned off to a computer, the contents of system memory are lost. Data that is to be stored long-term on a computer system thus is stored in other non-volatile memory devices. Most computer systems include a hard drive which is capable of permanently storing data on magnetic tape. Other removable drives, such as zip drives, CD-ROMs, DVD-ROMs, and the like, may also be used for long-term storage of data. In these types of media, the data is preserved, even when power is removed from the computer system.
Almost all portable computers, and some desktop computers, may be placed in a low power state to preserve power. Preservation of power is especially important in portable computers, where operating power may be provided from batteries. To extend the life of batteries in portable computers, and thus extend the amount of time that a user can operate a portable computer without recharging the batteries or finding an electrical source, most portable computers are capable of going into a sleep mode where minimal power is consumed. The sleep mode permits the computer system to be placed in standby, so that operation can resume when the user is ready, without requiring the system to boot.
As power management of portable computer systems has evolved, two different low power modes have been developed and used commercially. The first low power mode is known as “hibernation” or “hibernation to disk.” In this mode, which is the lowest power mode of the computer system other than power-off, the computer system consumes minimal energy. The hibernation mode can be analogized to a no-power bookmark of the existing state of the computer system. When the hibernation mode is entered, the system hardware state is copied to the hard drive. Because the hard drive is non-volatile memory, all power can then be removed from the system. Upon resume, the entire system state is copied from the hard drive image and restored to system memory and to the devices whose state was copied. Hibernation to disk typically is referred to as the “S4” state by the ACPI nomenclature.
In hibernation mode, the system memory (or RAM) is not powered. Hibernation to Disk has been referred to as “Zero volt suspend” because no power is required to sustain the system contents. Thus, the data in system memory is no longer available once the system enters the hibernation mode because the memory cells are not refreshed. When resuming from hibernation, a delay period is encountered as the working data is reloaded from the hard drive back to the system memory. The time required to access data from the hard drive is significantly longer than accessing data from system memory. Thus, there is a perceptible delay that occurs when data is loaded form the hard drive to the system memory after the hibernation mode is exited. In many instances the resume process from hibernation mode can take between 30 seconds to 1 minute, as the system memory and system devices are completely restored from the relatively slow hard drive memory.
Conventional Hibernation to Disk is implemented by powering down the system in response to a system event. The system event can be the manual selection of an icon or menu entry, the selection of one or more keys, or system inactivity. Because the hibernation mode results in the removal of power, the context of all system peripherals is read and then stored to the hard drive. Next, the contents of the system memory are copied to the hard drive. A hard drive file that is equal to the size of the memory to be stored is created, which holds a mirror image of the system memory. After the contents of system memory are backed up, a flag is set in non-volatile memory indicating that the system context has been completely saved. Once the flag is set, the power is removed causing the contents of volatile memory (such as DRAM and the context of peripheral devices) to be lost. When the system resumes operation, the system BIOS or operating system polls the nonvolatile flag bit that indicates that the hard drive contains valid system context. If the flag bit is set, the BIOS or operating system restores the system context from the hard drive before resuming system operation.
The second low power state is referred to as the “suspend” mode or “Suspend to RAM” mode. In the suspend mode, the system memory remains powered while the system is taken to a non-operational state. The advantage of keeping the system memory powered is that when operation is resumed, the system is ready within a very short period for operation, in the state last used by the operator. Thus, resuming from a suspend mode only takes a few seconds, because very little system context is moved. Suspend to RAM generally is preferred as a bookmark feature because of its “instant on” low latency resume time. Suspend to RAM is also called the S1, S2, or S3 power state by the ACPI nomenclature.
Conventional Suspend to RAM works by stopping the clocks to the system, while leaving the entire system power on. Because the power used by the system depends on the system clock speeds, removing the clock signals significantly lowers the system power. Suspend to RAM often is referred to as “Power on Suspend.” When the system resumes operation from Suspend to RAM, the clocks may simply be started to restore system operation. Another form of Suspend to RAM stores the context of certain system devices to system memory. Examples of the device contexts that may be saved include peripherals such as audio controllers, the state of the processor, the contents of the processor cache, and the like. Once the context of these devices is stored to system memory, the clocks to those devices are stopped and power is removed. The system memory, however, remains powered to maintain its contents. To resume operation, the system BIOS or operating system restores the context of the peripherals from system memory, and then system operation is resumed.
The hibernation mode has been preferred because little or no power is consumed while the system is in this state. Recent improvements in the circuitry used for Suspend to RAM, however, have minimized the power drain that occurs in suspend mode. However, Hibernation to Disk still has a key integrity advantage over Suspend to RAM, because Suspend to RAM relies on the use of volatile DRAM memory. If power is lost to the DRAM during suspend mo
Hewlett--Packard Development Company, L.P.
Iqbal Nadeem
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