Data processing system with power-fail protected memory module

Abstract: A data processing system preserves the contents of a volatile memory in the event of a power-loss and restores the contents upon a power-up. The system includes an AC line monitor (14) which signals when a power loss is imminent; volatile memory modules (26, 28); and a central processor (24) which executes programs in conjunction therewith. At any specific time during program execution, the volatile memory (26, 28) stores data indicative of the system's state. A backup disk drive (34, 36) is connected to each volatile memory module (26, 28) and is associated with a backup battery (38, 40). The backup battery (38, 40) is of limited capacity and only enables sufficient operation of the disk drive (34, 36) and volatile memory (26, 28) to enable a memory dump onto the disk drive (34, 36) from the volatile memory (26, 28). A logic circuit (50) is responsive to a signal from the line monitor (14) to activate the backup battery (38, 40) and to control the volatile memory module (26, 28) and the backup disk drive (34, 36) to effect a transfer of all stored data in the volatile memory (26, 28). Thus, upon a subsequent power up, a system state in existence at the time of the power loss can be reestablished by reading out the contents of each backup disk drive (34, 36) into its associated volatile memory module (26, 28).

Description: The present invention relates to a data processing system according to the preamble of claim 1. A data processing system of this type is known from the US-A-5,396,637. BACKGROUND OF THE INVENTION One reason for the increased success of multi-user computing systems arises from the fact that their designs include substantial provisions for coping with power failures. Such systems have facilities that afford the user the luxury of experiencing a loss of primary power, and enable the system to resume processing as if no loss of supply voltage had been experienced. In general, such systems require battery back-up or some other power supply replacement that is activated in the event of a failure of the A/C main supply. With the increasing complexity of multi-user computing systems, and a resulting geometric increase in the amount of available solid state memory in such systems, power fail protection requires substantially increased amounts of standby power. More specifically, the backup power supply must enable the data in the volatile memory bank to be stored prior to a total loss of supply voltage. The volatile memory must then be returned to the same state after power is restored. At typical speeds, using a disk to store data dumped from the volatile memory, substantial time may be required to accomplish such storage actions. For instance, if a multi-user system includes a 1-gigabyte quantity of data, such transfer would consume over 3 minutes of disk operating time. Future systems are expected to grow upwards of 4-gigabytes and thus, it would theoretically take over 10 minutes to save the data and another 10 minutes to reload. Recent advances in the disk drives have led to the introduction of extremely small disk drives that are both inexpensive and high capacity. For instance, one such disk drive employs 1.3 inch disks, is smaller than a normal cigarette package, stores 40 megabytes and is available at a cost of less than $400. Such disk drives enable the storage of substantial amounts of data in a small package at very low cost. The JP-A-4,283,825 discloses a semiconductor disk device, having a semiconductor memory, a plurality of memory access control parts which write and read data on and out of the semiconductor memory, a plurality of nonvolatile medium control parts which write the data read out by the memory access control part on a plurality of nonvolatile medium. A control means sends the data saving indication to the nonvolatile medium control parts and the memory access control parts and it is so constituted that the data stored in the semiconductor memory are equally divided and saved on the nonvolatile media. The data in the semiconductor memory are divided into equal parts, irrespective of their physical storage location, to the nonvolantile media. Accordingly, it is an object of this invention to provide a data processing system with a volatile memory module whose contents are protected in the event of a power failure. It is another object of this invention to provide a data processing system with power protected random access memory wherein nonvolatile memory modules are provided for the sole purpose of memory protection. It is yet another object of this invention to provide a memory protection system that enables a computer, after a power-off and a subsequent power-on to immediately reconstitute a memory state that existed at the power-off stage. These objects are achieved by the apparatus as set forth in claim 1. SUMMARY OF THE INVENTION A data processing system preserves the contents of a volatile memory in the event of a power-loss and restores the contents upon a power-up. The system includes an AC line monitor which signals when a power loss is imminent; volatile memory modules; and a central processor which executes programs in conjunction therewith at any specific time during program execution, the volatile memory stores data indicative of the system's state. A backup disk drive is connected to each volatile memory module and is associated with a backup battery. The backup battery is of limited capacity and only enables sufficient operation of the disk drive and volatile memory to enable a memory dump onto the disk drive from the volatile memory. A logic circuit is responsive to a signal from the line monitor to activate the backup battery and to control the volatile memory module and the backup disk drive to effect a transfer of all stored data in the volatile memory. Thus, upon a subsequent power up, a system state in existence at the time of the power loss can be reestablished by reading out the contents of each backup disk drive into its associated volatile memory module. DESCRIPTION OF THE DRAWING The Fig. is a block diagram of a preferred embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION Referring to the Figure, a power supply 10 receives its main supply from A/C line 12. Power supply 10 is provided with a line monitor module 14 which continuously monitors the potentials on A/C line 12 to determine any change in level thereon. In the known manner, line monitor 14, upon sensing a voltage change on line 12 that falls below a predetermined threshold, generates a signal on line 16 that a power failure is imminent. That signal is placed on a bus 18 which provides the main communication pathway for the data processing system. Power supply 10 also has a power switch 20 that controls the on or off state of power supply 10. A line 22 signals the state of power switch 20 to bus 18. The data processing system of Fig. 1 is provided with a central processing unit 24 and a plurality of associated random access memory modules (RAMs) 26, 28, etc. Each RAM is volatile in nature and provides working memory for CPU 24. The data processing system also includes a read-only memory 30 and one or more disk drives 32 interconnected with bus 18. Each RAM module is provided with a backup disk drive (e.g., disk drives 34, 36 for RAM modules 26 and 28, respectively). Each RAM module also has associated therewith a backup rechargeable battery (e.g., 38, 40) and an error correction control generating module (e.g., 42 and 44). The RAM in the data processing system of the Figure is segregated into memory storage capacity sizes that match the data storage capacity of the respective backup disk drives. Thus, each RAM module (e.g., 26) has the same data storage capacity as its backup disk drive (e.g., 34). In this manner, a backup disk drive is capable, at any time, of storing the entire contents of its associated RAM module. Since each backup disk drive is a dedicated disk drive, it serves no function other than to provide for backup storage in the event of a power loss. ECC modules 42 and 44 provide for the generation of error correction codes between the respective RAMs and their backup disk drives. Each RAM module, backup disk drive, battery and ECC module may be packaged on a single, pluggable circuit board (shown schematically by dashed boxes 45 and 47). In the 32 megabyte configuration shown in the figure, data in RAM module 26 can be fed to backup disk drive 34 in less than 10 seconds. Thus, battery 38 merely needs to power RAM 26 and backup disk drive 34 for the 10 second period necessary to perform the data transfer operation. Of course, battery 38 should have some additional capacity so as to provide for a safety margin. Nevertheless, since the data transfer can occur so quickly, battery 38 need not have substantial storage capacity. A power fail logic module 50 provides the necessary control signals to RAMs 26, 28 and backup disk drives 34 and 36, respectively, to enable data transfers therebetween. Similarly, power fail logic module 50 switches batteries 38 and 40 into the circuits to enable the functioning of their respectively connected backup disk drives and RAMs. In operation, line monitor 14 continually monitors AC input line 12 to determine when, and if, the voltage level thereon falls below a predetermined threshold. Upon sensing such a fall, line monitor 14 generates a power fail imminent signal on line 16 which is fed by bus 18 to power fail logic module 50. Power fail logic module 50 responds by causing batteries 38 and 40 to switch into their respective circuits and signals RAMs 26 and 28 to dump their data onto their respectively connected backup disk drives 34, 36. As each backup disk drive 34 and 36 is also powered directly from power supply 10, it is up to speed when the signal to transfer data emanates from power fail logic module 50. Batteries 38 and 40 maintain the rotation speed of their respectively connected backup disk drives, at least until after the data transfer from the respectively connected RAMs is completed. Upon a subsequent power up, CPU 24 causes each of backup disk drives 34 and 36 to read their stored data back into their respectively connected RAM modules 26 and 28. Thus the system state is reestablished identically to that which was in existence at the time of the shut down. If the data processing system is a portable personal computer the system shown in the fig. also enables the system state to be saved upon power switch 20 shutting off the system. Under such conditions, the power off signal on line 22 may be caused to enable power fail logic 50 to institute the above-described backup procedure so as to enable the machine state of the data processing system to be reestablished upon power switch 20 being turned on again. It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. For instance, the capacity of each backup disk drive can be larger than its associated RAM capacity, with the excess disk storage capacity being used for storage of error correction code. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.

Claims: A data processing system wherein data stored in a volatile memory is preserved in the event of a power interruption, said data processing system comprising: power monitor means (14) coupled to a power source (12) for signalling when a power interruption is imminent; volatile memory means (26, 28); central processing means (24) for executing programs in conjunction with said volatile memory means (26, 28), said volatile memory means (26, 28) storing data indicative of a system state of said data processing system at times during execution of said programs; backup disk drive means (34, 36) connected to said volatile memory means (26, 28); backup battery means (38, 40) connected to said backup disk drive means (34, 36) and said volatile memory means (26, 28); and logic means (50) responsive to a signal from said power monitor means (14) to activate said backup battery means (34, 36) and to control said volatile memory means (26, 28) and said backup disk drive means (34, 36) to effect a transfer of all stored data in said volatile memory means (26, 28) to said backup disk drive means (34, 36), whereby, upon a subsequent power up, a system state in existence at said signal from said power monitor means (14) can be reestablished by reading out the contents of said backup disk drive means (34, 36) to said volatile memory means (26, 26), wherein said backup disk drive means (34, 36) is comprised of a plurality of disk drives (34, 36) and said volatile memory means (26, 28) is comprised of a plurality of random access memory (RAM) modules (26, 28), each of said RAM modules (26, 28) is connected to a separate backup disk drive (34, 36) via a dedicated backup bus, and each of said backup disk drives (34, 36) has sufficient memory capacity to accommodate all data in a connected RAM module (26, 28); each of said connected RAM modules (26, 28) and backup disk drives (34, 36) is provided with a dedicated backup battery (38, 40), having sufficient power capacity to enable a complete transfer of data in said RAM module (26, 28) to the corresponding backup disk drive (34, 36) each of said RAM modules (26, 28) and connected backup disk drives (34, 36) is connected with an error correction code generating means (42, 44) for assuring data integrity of data transferred between a RAM module (26, 28) and a backup disk drive (34, 36); and each of said RAM modules (26 28) , connected backup disk drives (34, 36), dedicated batteries (38, 40) and error correction code generating means (42,44) are mounted on a removable memory card (45, 47) as an integral unit. The system of claim 1, characterized in that the power monitor means (14) comprises line monitor means for signalling a power loss. The system as in one of the preceding claims wherein said backup battery means (38, 40) is provided with a predetermined electric storage capacity and is rechargeable, said back-up battery means (38, 40) enabling a complete transfer of data in said volatile memory means (26, 28) to said backup disk drive means (34, 36), said predetermined electric storage capacity enabling said backup battery means (38, 40) to power said transfer of data with a power safety margin. The system as in one of the preceding claims, further comprising power switch means (20) coupled to the power source (12) for said data processing system for controlling the on/off state of said power source (12), wherein said power monitor means (14) comprises on/off monitor means for signalling when said power source (12) is off.

Inventors: HARWELL JOHN CECIL, RUSNACK MICHAEL R, HARWELL, JOHN CECIL, RUSNACK, MICHAEL R.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1993
Main classification: G06F11
IPC codes: G06F11, G06F12, G06F1