Abstract:
A data preservation system for flash memory systems with a host system, the flash memory system receiving a host system power supply and energizing an auxiliary energy store therewith and communicating with the host system via an interface bus, wherein, upon loss of the host system power supply, the flash memory system actively isolates the connection to the host system power supply and isolates the interface bus and employs the supplemental energy store to continue write operations to flash memory.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/032,332 filed Dec. 20, 2001, entitled “SYSTEM AND METHOD FOR PREVENTING DATA CORRUPTION IN SOLID-STATE MEMORY DEVICES AFTER A POWER FAILURE,” which is hereby incorporated by reference and which claims the benefit of U.S. Provisional Application No. 60/259,597, filed Dec. 22, 2000, entitled “SYSTEM AND METHOD FOR PREVENTING DATA CORRUPTION IN SOLID-STATE MEMORY DEVICES AFTER A POWER FAILURE”, the entirety of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of Invention 
     The invention relates to saving data and avoiding data corruption in flash memory systems following a power failure and, in particular, to a system and method to actively isolate the flash memory system from a host system and employ an energy storage bank to facilitate storing data to flash memory following the power failure. 
     2. Description of Related Art 
     Solid state storage devices, such as Dynamic Random Access Memory (RAM) and Static Random Access Memory (SRAM), have fast access times, require low power, and are generally more durable and compact than magnetic disk drives, but are also more expensive and are volatile, requiring constant power to maintain their memory. As a result, DRAM and SRAM devices are often utilized in electronic systems as temporary memory in addition to non-volatile storage media. 
     Another type of solid state storage device is a Flash EEPROM device (hereinafter referred to as flash memory). Unlike DRAM and SRAM devices, flash memory systems are non-volatile and retain their memory in the absence of a power source. However, flash memory shares the low power, compactness, and lack of moving parts advantages of solid-state memory and, for this reason, for many applications, flash memory systems are a desirable alternative to conventional magnetic disk drives. 
     Current flash memory systems typically comprise a processor-based system controller, a data buffer, and an array of flash memory chips especially designed for such a system. The flash memory system typically communicates with and receives system power from a host electronic device, such as a computer, digital camera, etc. An interface bus provides a data conduit between the host and the flash system. The controller directs read and write operations between the flash memory devices and the buffer. 
     One concern with flash memory systems is that writing data to the flash memory takes some time and it is desirable that, in case of a power failure, incoming data be successfully written to the non-volatile flash memory before the data is lost. One particular hurdle to be overcome is that in case of a power failure other circuit elements, including the host device, can drain power that would otherwise be available to flush the volatile RAM to the non-volatile flash memory. It is also advisable to terminate new incoming data from the host as this data can be readily corrupted by the power failure and it is preferred to not store potentially corrupted data. 
     SUMMARY OF THE INVENTION 
     Inventive methods and systems for preserving data in memory systems. In one embodiment, a flash memory system is decoupled from a host system after the detection of a power failure. In another embodiment, an auxiliary energy source is used to complete memory write operations. 
     In another aspect of the invention, a data preservation system comprises a flash memory system that communicates with a host system. The flash memory system is in communication with a host system power supply that energizes a auxiliary energy store. The flash memory system is also in communication with the host system via an interface bus, wherein, upon loss of the host system power supply, the flash memory system actively isolates the connection to the host system power supply and isolates the interface bus and employs the auxiliary energy store to complete write operations to flash memory. 
     In another aspect, the invention is a data preservation system for flash memory systems receiving a power supply and experiencing power failure thereof, the data preservation system comprising a detection circuit in communication with the power supply, an auxiliary power source, an isolation circuit isolating the auxiliary power source upon a power failure, and controller circuitry configured to store data in volatile memory into flash memory. In particular aspects, the volatile memory comprises a tri-state buffer, the detection circuit comprises a voltage detector, and/or the auxiliary power source comprises capacitors. 
     The invention is also a method of preserving data in flash memory systems experiencing a power failure, the method comprising charging an auxiliary power source with a supply voltage, detecting a loss of power of the supply voltage, isolating the auxiliary power source, and utilizing the auxiliary power source to store data stored in volatile memory into flash memory and, in a certain aspect, includes isolating the auxiliary power source comprises opening a relay interconnecting the supply voltage and the auxiliary power source. 
     Another aspect of the invention is a memory device storing data stored in volatile memory into non-volatile memory wherein, upon loss of power to the memory device, at least one external connection of the device is isolated. In particular aspects the external connection comprises at least one of a connection to a power supply and a connection to a data interface and/or the non-volatile memory comprises a flash chip. 
     A further aspect of the invention is a method of storing data from volatile memory to non-volatile memory, the method comprising monitoring a power supply and, upon detecting a power failure of the power supply, isolating the non-volatile memory from external connections. One certain aspect includes isolating the non-volatile memory from external connections comprises isolating a power supply connection and a data interface connection. 
     Yet another aspect of the invention is a data preservation system comprising a power detector, an auxiliary power source, an isolator adapted to isolate the auxiliary power source, and a data store storing data into non-volatile memory powered by the auxiliary power source and in a particular aspect the non-volatile memory comprises a flash card. 
     The invention further is a method for storing data, the method comprising detecting a power reduction, isolating an auxiliary power source, and storing data into non-volatile memory using the auxiliary power source. 
     The invention also includes means for preserving data comprising: means for detecting loss of power, means for providing auxiliary power, means for isolating the means for preserving data upon detection of loss of power, and means for storing data in a non-volatile manner. 
     These and other objects and advantages will become more fully apparent from the following description taken in conjunction with the accompanying drawings. For purposes of summarizing the invention, certain aspects, advantages and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a high level block diagram of one embodiment of a host system and a flash memory system; 
         FIG. 2  is high level block diagram of one embodiment of a data preservation system for a flash memory system; 
         FIG. 3  is a circuit schematic of one embodiment of a data preservation system for flash memory systems after a power failure; and 
         FIG. 4  is a flow chart of one embodiment of a method of preserving data in a flash memory system after a power failure 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Systems and methods for storing data and storing data following a power failure for flash memory systems are disclosed herein. In order to fully specify the preferred designs, various embodiment-specific details are set forth. It should be understood, however, that these details are provided to illustrate embodiments of the invention, and are not intended to limit the scope of the invention. 
       FIG. 1  illustrates one embodiment of a electronic system  100  comprising a host system  102  and a flash memory system  110  that can implement embodiments of the system and method for storing data disclosed herein. The host system  102  can comprise a computer, digital camera, PDAs, or other electronic devices requiring non-volatile data storage. The flash memory system  110  stores data for the host system  102  in a non-volatile manner, and the two communicate by way of a system interface  104 . The host system  102  uses the system interface  104  to deliver commands to the flash memory system  110  to read or write blocks of user data, identifying a specific block of data with an address, and to receive data from the flash memory system  110 . The host-provided logical address may be presented in the form of a logical block address, a cylinder-head-sector number, a linear byte address, or some other identifying technology. 
     On receipt of such a command from the host system  102 , a controller  112  in the flash memory system  110  translates the host-provided address into a Valid Flash Device Block Address, or Valid Row Address (VRA). In other embodiments, the controller  112  can comprise controller circuitry, processor circuitry, processors, general purpose single-chip or multi-chip microprocessors, digital signal processors, embedded microprocessors, micro-controllers, and the like. In this embodiment, the controller  112  is resident in the flash memory system  110 . In an alternative embodiment, the controller  112  can reside in the host system  102  or alternatively, separately from the host system  102  and the flash memory system  110  and the like. 
     When the command is a write command, the controller  112  transfers data from the system interface  104  into an intermediate data buffer  118 , and from the data buffer  118  to a storage location that corresponds to the received VRA, the location being in an array of one or more flash memory devices  120 . 
     When the command is a read command, the controller  112  orchestrates a transfer of data from one or more locations in the array of flash memory devices  120  that correspond to the host-provided address received via the system interface  104 . The controller  112  transfers the data from the memory array  120  into the intermediate data buffer  118 , and thence from the data buffer  118  to the host system  102 , again by way of the system interface  104 . 
     In the embodiment illustrated in  FIG. 1 , the flash memory devices  120  are provided in an array of flash memory devices or chips. However, the flash memory  120  can also be implemented on an individual chip, device, or other component, or on a plurality or variety of such chips, devices, or other components in alternative embodiments of the invention. 
       FIG. 2  is a functional block diagram of one embodiment of the invention illustrating the general system architecture in greater detail. In this embodiment, the flash memory system  110  receives a supply voltage, V cc    122 . V cc    122 , in this embodiment, is provided by the host system  102  and during normal operation is continuously available to the flash memory system  110 . In an alternative embodiment, V cc    122  can be provided by other power sources separate from the host system  102 . 
     In the event of failure to maintain V cc    122  such as when the host system  102  loses power, or when the flash memory system  110  is disconnected from V cc    122 , The flash memory system  110  is adapted to detect the loss of power. In one embodiment, the flash memory system  110  isolates the flash memory system  110  from V cc    122  and the host system  102 , and stores data to the flash memory devices  120  in a manner that will be described in greater detail below. 
     The flash memory system  110  comprises a supply voltage V cc  isolator  124 . The V cc  isolator  124 , in this embodiment, is a circuit that can actively sever the connection between V cc    122  and the flash memory system  110  to avoid the host system  102  acting as a load on the flash memory system  110 . The flash memory system  110  also comprises a power failure detector  126  that can detect the loss of V cc    122  from the flash memory system  110 . In this embodiment, the power failure detector  126  directs the V cc  isolator  124  to sever the connection to V cc    122  and terminate pending flash memory system write operations if the power failure detector  126  detects the loss of V cc    122 . 
     The flash memory system  110  also comprises an auxiliary power source  130  that, during normal operation, receives V cc    122  via the V cc  isolator  124 . In case of loss of V cc    122 , the auxiliary power source  130  is actively isolated from the host system  102  and provides temporary operating power to the flash memory system  110  to continue pending write operations in a manner that will be described in greater detail below so as to avoid data corruption. 
       FIG. 3  is a schematic of one embodiment of the invention and shows a circuit performing the functional aspects of the invention as shown in  FIG. 2  in greater detail. As shown in  FIG. 3 , the flash memory system  110  receives a supply voltage, V cc    122 , in this embodiment from the host system  102 . V cc    122  is provided to the power failure detector  126 , which in this embodiment comprises a voltage detector U 2   132 . The voltage detector  132  normally holds a signal line /OUT on pin  1  high. The /OUT signal is connected via a 4.7 kΩ resistor to the base of a transistor Q 1   134 , causing transistor  134  to conduct. The conduction of transistor  134  causes a relay U 1   136  to close. Relay  136 , in a closed condition, passes V cc    122  to an auxiliary supply node  142  and, via a resistor  140 , to the auxiliary power source  130 . In this embodiment, the auxiliary power source  130  comprises a bank of  20  capacitors connected in parallel. 
     The collector of the transistor  134  is connected via a 10 kΩ resistor to the auxiliary supply node  142 . The auxiliary supply node  142  is also connected via a normally forward biased diode  144  to the supply voltage, V cc    122 . The collector node of transistor  134  defines a power fail signal  146  which is normally low. The power fail signal  146  is provided to inverted chip enable pins of two buffers U 3   150  and U 4   152 . The buffers  150 ,  152  are connected to the host system  102  via the system interface  104  and store data as is it exchanged between the host system  102  and the flash memory system  110 . 
     The /OUT signal is also connected via a 4.7 kΩ resistor to the base of a transistor Q 2   154 . The emitter of the transistor  154  is connected via a 470 Ω to a relay U 5   156  and then to the auxiliary supply node  142 . The transistor  154  is normally off and relay  156  is normally open. 
     If the voltage detector  132  detects a loss of V cc    122  on pin  2 , the voltage detector  132  lowers the /OUT signal which causes transistor  134  to stop conducting and the power fail signal  146  to go high. This causes relay  136  to open which actively severs the connection to the supply voltage V cc    122  and isolates the auxiliary supply node  142  from the supply voltage V cc    122  via the now reverse biased diode  144 . Transistor  154  starts conducting which causes relay  156  to close thereby shorting across the resistor  140  and providing the charge of the auxiliary power supply  130  directly to the auxiliary supply node  142 . 
     The power fail signal  146  going high causes the buffers  118  comprising, in this embodiment, buffers  150  and  152  to stop conducting. The buffers  150 ,  152  tri-state and a plurality of terminating resistors  160  terminate the inputs of the buffers  150 ,  152  to inhibit open circuits which would other wise result if the flash memory system  110  is physically separated from the host system  102 . Terminating the activity of the buffers  150 ,  152  inhibits the flash memory system  110  from storing data that the buffers  150 ,  152  may receive from the host system  102  that may be corrupted by the power failure. 
     Isolating the auxiliary power supply  130  from the host system  102  enables the charge of the auxiliary power supply  130  to be available for completing any write operations that the flash memory system  110  was conducting when the power failure occurred without also attempting to maintain power to other circuits in the host system  102  or others that are normally supplied with the supply voltage V cc    122 . This aspect of the invention also facilitates updating any File Access Tables (FAT) or other data organization information such that stored data can be more readily read and accessed when normal operation of the electronic system  100  returns. 
       FIG. 4  is a functional flow chart indicating the operation of one embodiment of the invention. State  200  indicates normal operation of the flash memory system  110  with the host system  102  wherein power is provided normally to the flash memory system  110  and the auxiliary power source  130  is charged, but not used. State  202  indicates detection of a power failure by the flash memory system  110 . As previously described, state  202  indicates that the normally supplied voltage has dropped below a predetermined threshold or is otherwise no longer available to the flash memory system  110 . 
     State  204  follows upon the occurrence of state  202  and indicates the isolation of the auxiliary power source  130 . State  206  also follows the occurrence of state  202  and indicates the isolation of the buffers  118  from the host system  102 . This aspect of the invention inhibits storing data that may be received in the buffers  118  that may be corrupted by the loss of power from being stored. 
     State  210  indicates storing the data in flash memory. State  210  comprises otherwise normal storage of data to the flash memory devices  120  as directed by the flash controller  112 , except that after a power failure, the flash controller  112  and the flash memory devices  120  receive operational power from the auxiliary power source  130  as previously described. State  212  is an end state wherein normal supply voltage is again supplied to the flash memory system  110  and normal operation resumes or the auxiliary power source  130  is depleted after the data is stored to the flash memory devices  120  in state  210 . Although  FIG. 4  indicates a sequential flow, is should be understood by one of skill in the art that the operations described for states  202 ,  204 ,  206 , and  210  can occur partially or substantially in parallel. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.