Abstract:
This invention provides a method to operate a terminal ( 100 ), as well as a terminal that operates in accordance with the method. The method includes, in response to initiating a data write operation with a non-volatile memory device ( 132 ), activating a sensor ( 190 ) that is capable of detecting that the terminal is falling; during the write operation, monitoring the sensor to determine if the terminal is falling and, if it is determined that the terminal is falling, terminating the write operation and executing a non-volatile memory shutdown procedure, else, if it is determined that the terminal is not falling, completing the write operation and deactivating the sensor.

Description:
TECHNICAL FIELD 
     This invention relates generally to data storage memory devices and components and, more specifically, relates to the protection of data stored in a non-volatile memory device during a physical shock to a unit that contains the memory device. 
     BACKGROUND 
     All solid state non-volatile memory devices that are known to the inventors, including Flash memory, MultiMedia Card (MMC), and Subscriber Identity Module (SIM), are vulnerable to an abrupt termination of power. As but one example, a file-control system or the memory contents can be corrupted if the power-off occurs during a write sequence, such as during a file-control table update procedure. While this problem can exist in any electronic system that incorporates one or more non-volatile memory devices, the problem is especially acute in handheld portable electronic systems that are subject to frequency handling by the user. Examples of such systems include, but are not limited to, cellular telephones, personal digital assistants (PDAs), portable computers, image capture devices such as digital cameras, gaming devices, music appliances and handheld units or terminals that incorporate combinations of two or more such functions. 
     The abrupt and unexpected interruption of power can occur when the terminal is dropped due to one or more of a number of occurrences. For example, dropping the terminal can result in the movement or expulsion of the battery, leading to an abrupt and uncontrolled power-off condition. Dropping the terminal may also result in the movement or expulsion of the memory component itself, such as a plug-in memory card. This can also lead to an abrupt and uncontrolled power-off condition, as well as an abrupt termination of the memory component digital input/outlines and the signals conveyed thereby. 
     It is known in the art to provide some protection for rotating magnetic media (a hard disk drive, or HDD). For example, U.S. Pat. No. 5,982,573, entitled “Disk Drive and Method for Minimizing Shock-induced Damage”, describes a disk drive having a fall detection control system that detects when the disk drive is in a free fall, and takes precautionary protective action to minimize physical damage from any resulting shock upon impact. The disk drive includes an accelerometer device that measures acceleration of the disk drive along three mutually orthogonal axes x, y, and z, and resolves the measurement into respective vectors. A processor is programmed to compute a net acceleration of the disk drive, compare the net acceleration with a selected acceleration threshold level, measure a duration that the net acceleration exceeds the acceleration threshold level, compare the measured duration with a selected reference time period, and output a warning signal when the measured duration exceeds the reference time period. Upon receipt of the warning signal, a controller initiates protective routines in preparation for shock. 
     Also of interest is U.S. Pat. No. 6,567,709, “Integrated Monitoring, Diagnostics, Shut-down and Control System”; U.S. Pat. No. 5,991,114. “Disc Drive Having Gram Load Reducer and Method of Operating Gram Load Reducer”, and U.S. Pat. No. 5,227,929, “Portable Computer Hard Disk Protective Reflex System”. 
     Prior to this invention, the inventors are not aware of any protective mechanisms or methods for solid state memory devices to avoid data corruption due to an impact after a fall. 
     SUMMARY OF THE PREFERRED EMBODIMENTS 
     The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings. 
     In one aspect this invention provides a method to operate a terminal. The method includes, in response to initiating an operation, such as a data write operation, with a non-volatile memory device, activating a sensor that is capable of detecting that the terminal is falling; during the operation, monitoring the sensor to determine if the terminal is falling and, if it is determined that the terminal is falling, terminating the operation, else, if it is determined that the terminal is not falling, completing the write operation and deactivating the sensor. Terminating the operation can include executing a non-volatile memory shutdown procedure. 
     The sensor may be operated at a sampling rate that is selected to minimize sensor power consumption within constraints imposed by at least one characteristic, such as the amount of time required to execute the shutdown procedure, of the non-volatile memory device that the write operation is directed to. 
     Further aspects of this invention relate to a terminal that operates in accordance with the method, and a wireless communications terminal having an accelerometer-based sensor that operates in accordance with the method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other aspects of these teachings are made more evident in the following Detailed Description of the Preferred Embodiments, when read in conjunction with the attached Drawing Figures, wherein: 
         FIG. 1  is a block diagram showing a mobile station that is constructed and operated in accordance with this invention; and 
         FIG. 2  is a logic flow diagram of a method to operate the mobile station of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a simplified block diagram an embodiment of a wireless communications terminal or mobile station  100  in accordance with this invention. It should be noted, however, that this invention applies to many different types of handheld, portable and other types of terminals, including those that have no wireless communications capability. For example, the terminals that can benefit from the use of this invention include, but are not limited to, cellular telephones, such as the one depicted in  FIG. 1 , as well as gaming devices, digital cameras, PDAs, navigation (e.g., GPS) devices, data logging devices, portable bar code scanners, Internet appliances and, in general, any type of electronic equipment that includes at least one non-volatile memory device that is writable during the normal operation of the device. As employed herein a non-volatile memory device can be a device that is designed and engineered to retain data when the system operating power is removed (e.g., Flash memory devices), as well as a volatile memory device (e.g., a static RAM) that is packaged or otherwise connected to a separate backup battery or a charge storage capacitor. 
     The mobile station  100  typically includes a control unit or control logic, such as a microcontrol unit (MCU)  120  having an output coupled to an input of a display  140  and an input coupled to an output of a keyboard or keypad  160 . The mobile station  100  may be a handheld radiotelephone, such as a cellular telephone or a personal communicator. 
     The MCU  120  is assumed to include or be coupled to some type of a memory, including a non-volatile memory (NVM)  132  for storing an operating program and other information, as well as a volatile memory  130  for temporarily storing required data, scratchpad memory, received packet data, packet data to be transmitted, and the like. The operating program is assumed, for the purposes of this invention, to enable the MCU  120  to execute the software routines, layers and protocols required to implement the methods in accordance with this invention, as well as to provide a suitable user interface (Ul), via display  140  and keypad  160 , with a user. Although not shown, a microphone and speaker are typically provided for enabling the user to conduct voice calls in a conventional manner. 
     Although not germane to an understanding of this invention, the mobile station  100  also contains a wireless section that includes a digital signal processor (DSP)  180 , or equivalent high speed processor or logic, as well as a wireless transceiver that includes a transmitter  210  and a receiver  220 , both of which are coupled to an antenna  240  for communication with the network operator. At least one local oscillator, such as a frequency synthesizer (SYNTH)  260 , is provided for tuning the transceiver. Data, such as digitized voice and packet data, is transmitted and received through the antenna  240  in accordance with an air interface standard that may conform to any standard or protocol. 
     The mobile station  100  also includes an free fall sensor, embodied in this non-limiting embodiment as an acceleration sensor  190 , such as an accelerometer that has three sensitive axes. The acceleration sensor  190  is used to detect that the mobile station  100  is falling, and thus senses the acceleration of the mobile station  100  due to gravity. The output of the acceleration sensor  190  is designated as  190 A, while an input signal to the sensor  190  that activates the sensor is designated as Activate  190 B. 
     The NVM  132  can include a single type of memory, or it may present a plurality of different memory types, such as two or more of Flash memory, MultiMedia Card (MMC) memory and a Subscriber Identity Module (SIM) that contains a non-volatile memory device. Each NVM  132  component is assumed to be responsive to a specified signal with which it is either shut down, put into a sleep mode, or placed into a safe mode in which no corruption of stored data can occur. This signal is shown in  FIG. 1  as Control (CNTL)  132 A that is sourced by the MCU  120 . In other embodiments the CNTL signal  132 A could be sourced by the DSP  180 , or by dedicated logic. 
     When the acceleration sensor  190  detects a free-fall situation, its sends a pre-defined signal to the MCU  120  over signal line  190 A. The MCU  120  in response sends the predefined shutdown signals to each of the NVM  132  components via the Control signal line  132 A. 
     In a preferred embodiment, the acceleration sensor  190  is only turned on or activated, i.e., placed in a full power mode of operation with the Activate signal  190 B, when a write operation is being performed to one of the NVM  132  components. In this way a power savings is realized, as the mobile station  100  will typically be powered by an internal battery (not shown). 
     Referring to  FIG. 2 , at Block  300  the controller (MCU)  120  receives (or originates) a write command for the NVM  132 . In response the MCU  120  activates in Block  310  the sensor  190  via signal line  190 B, and also activates a write memory command to the NVM  132  (Block  320 ). Continuing for convenience at the acceleration sensor  190 , at Blocks  330 ,  340  and  360  a sensing loop is executed to get the sensor reading and determine if a free fall condition (shock) is indicated. The loop is executed until the NVM  132  write operation is indicated as being finished by the output of Block  420  or a free fall condition has been indicated. If a free fall condition is indicated, Block  340  transitions to Block  350  to send a shutdown interrupt (CNTL  132 A) to the NVM  132 . Assuming that the write operation concludes normally, Block  360  transitions to Block  370  to deactivate the acceleration sensor  190  via signal line  190 B, and then transitions to Block  380  to acknowledge completion. 
     At the NVM  132 , in response to the activation of the write command at Block  320 , the data is written to the memory at Block  390 , and a loop  390 ,  400 ,  410  is executed until the NVM write operation is signaled as being completed at Block  410 . Block  410  sends the completion signal to controller block  420 , which sends the acknowledgment of the write operation being completed to Block  360  of the sensor  190 . The write loop Block  400  tests to see if the shut down interrupt has been generated by the controller Block  350  (CNTL  132 A is asserted). If the shut down interrupt is generated, then Block  400  transitions to Block  430  to terminate the write operation, and execute the shutdown procedure that is specific to the NVM  132 . For example, and depending on the type of NVM, the shutdown procedure can entail actually shutting off the NVM  132 , or putting the NVM  132  into a sleep (low power consumption) mode, or otherwise placing the NVM  132  into some type of safe mode in which no corruption of stored data is likely to occur. In some embodiments the safe mode may simply be an idle mode, where no active read or write operation is occurring. Block  430  may then transition to controller Block  440  to acknowledge the NVM  132  shutdown has occurred, and the method ends. 
     During the use of the preferred embodiments of this invention some variations to the foregoing methods can be made. For example, in response to receiving the write command at Block  300 , the controller  120  may first check the free fall sensor at  340  to ensure that a free fall condition is not currently indicated before executing a transition to block  320  to activate the write command. Further by example, for those storage technologies where the NVM  132  should be actively shut down after sensing a free fall condition, such as when using a hard disk drive (HHD), the method shown in  FIG. 2  may be used as well for read operations, and not just for write operations. 
     It is preferred to partition critical data into small enough portions that a write operation can be accomplished during the free fall time. 
     It is also within the scope of this invention for the MCU  120  to optimize the sampling frequency (and hence power consumption) of the acceleration sensor  190  when a drop threshold is known, as described below. 
     A suitable free fall detection method is as follows (Blocks  330 ,  340 ,  360  of  FIG. 2 ). During free fall, the acceleration is always one g. Thus the acceleration sensor  190  output can be activated when the measured acceleration reaches a predetermined level (such as 0.4-1 g due to the need to account for sensor errors). The time of free fall is measured, giving the distance fallen as x(t)=g*t 2 /2. A threshold time of free fall is preferably made as long as possible, to allow vibrations to be distinguished from a free fall. When the measured x(t) exceeds the predefined threshold X 0 , the Control signal  132 A is asserted to the NVM  132  to place the NVM(s)  132  into a state where the corruption of stored data is unlikely, should the mobile station experience an impact on a hard surface (Block  430  of  FIG. 2 ). 
     In the prior art a time threshold of about 125 msec is known to correspond to a drop of about seven centimeters, which is suggested as a threshold for initializing a HDD protection mechanism. 
     However, for a mobile terminal, such as the mobile station  100 , the thresholds of interest are somewhat different. A standard mobile station  100  drop test height is 1.5 m. Because of the acceleration, the threshold time (T) increases mores slowly than the altitude (X), namely: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                   
                 X0 
                 T0 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0.5 
                 m 
                 320 msec 
               
               
                 1 
                 m 
                 450 msec 
               
               
                 1.5 
                 m 
                 550 msec 
               
               
                   
               
             
          
         
       
     
     Assume that the maximum time required to activate the NVM  132  shutdown sequence is TM. An exact value for TM can be difficult to determine, due to the requirements of different NVM  132  technologies. However, for an exemplary MMC card the value of TM is in the range of a few tens of milliseconds. Thus, a non-limiting and exemplary value of 100 ms is used below. 
     Let the sampling period of the acceleration sensor  190  be FS Hz, which means that the acceleration is sampled once every TS=1/FS seconds. There is thus a “dead time” of TM+1/FS seconds. Thus, the actual threshold time TT available for the measurement of free fall becomes:
 
 TT=T 0 −TM−TS =sqrt(2*×0/g)− TM −1 /FS. 
 
     This allows a minimum value for FS to be defined, when it is desired that TT be above a defined minimum TTMIN in order to eliminate spurious effects. Thus, the sampling of the acceleration sensor  190  during a NVM  132  write operation can be optimized to conserve battery power. 
     As a numerical example: assume that TTMIN=100 msec is a sufficient amount of time, assume that TM=100 msec, and assume that the drop height threshold is one meter, then TT&gt;TTMIN=0.1 s=0.45 s−0.1 s−1/FS, which means that an acceleration sensor  190  sampling frequency of 4 Hz is adequate. If the acceptable drop altitude is increased to 1.5 m, then the sampling frequency can be 2.9 Hz, while a reduced 0.5 m drop height requires a 8.3 Hz sampling frequency. 
     This variability allows the use of an optional feature in the basic drop detection NVM  132  shutdown algorithm: i.e., if there are large variations between the TM for various NVM  132  components, then a Sensor Activation flag (Activate Sensor Block  310  of  FIG. 2 ) can include the TM for the NVM  132  component which launched the sensor (or the required sampling rate directly). That is, the acceleration sensor  190  sampling rate can be made adaptive, and established at Block  310  depending on which NVM  132  component the write operation is being performed to. This allows the sampling rate to be minimized to accommodate the specific NVM component which is to be protected. For example, and assuming the case of a one meter drop distance: if TM=0.1 s, then FS=4.0 Hz (as above); if TM=0.05 s, then FS=3.3 Hz, and if TM=0.01 s, then FS=2.9 Hz. 
     The resulting approximately 30% reduction in sampling rate (and roughly the same in power consumption) can be quite significant in the mobile station  100 . 
     The use of this invention is advantageous in that it minimizes the chance for the corruption of NVM data due to inadvertently dropping the mobile station  100 . This is especially advantageous in the case of memory cards, such as a SIM card, that can be reused in another mobile station or terminal in the event that the dropped mobile station is damaged. 
     In another embodiment of this invention acceleration sensor  190  sends the free fall signal  190 A directly to each NVM  132 , such as by a shared bus (shown as a dashed line  190 A′ in  FIG. 1 ). While this is a faster operating solution, since the MCU  120  is bypassed, its use implies that either the NVM memory  132  components convert the free-fall signal to a shutdown signal, or that the acceleration sensor  190  generates and transmits the appropriate NVM  132  shutdown signal(s) (CNTL  132 A). 
     Based on the foregoing description it should be apparent that a non-limiting aspect of this invention is a computer program embodied on a computer readable storage medium, such as the memory  130  in  FIG. 1 , that is comprised of instructions to direct a computer, such as the MCU  120  in  FIG. 1 , that is embodied in an enclosure, such as the mobile station  100 , to be responsive to initiating an operation, such as read operation, a write operation, or a read/modify/write operation, with a non-volatile memory device  132  to activate a sensor  190  that is capable of detecting that the enclosure is falling. During the operation the instructions direct the computer to monitor the sensor to determine if the enclosure is falling and, if it is determined that the enclosure is falling, to terminate the operation and to execute a non-volatile memory shutdown procedure. If it is determined instead that the enclosure is not falling, the operation is completed and the sensor is deactivated. 
     Monitoring can include operating the sensor at a sampling rate that is selected based on the type of non-volatile memory device that the operation is directed to; or operating the sensor at a sampling rate that is selected based on an amount of time required to execute the non-volatile memory device shutdown procedure; or operating the sensor at a sampling rate that is selected based on a predetermined minimum threshold distance over which the enclosure can fall; or operating the sensor at a sampling rate that is selected to minimize sensor power consumption within constraints imposed by at least one characteristic of the non-volatile memory device that the operation is directed to. The sensor may be operated at a sampling rate that is based on more than one of these criteria, either alone or in combination with even further criteria. 
     The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the best method and apparatus presently contemplated by the inventors for carrying out the invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. As but some examples, the use of other types of free fall sensors, such as a barometer/altimeter or a proximity sensor (acoustic or optical), may occur to those skilled in the art, as may also the use of other types of NVM  132  components. However, all such and similar modifications of the teachings of the preferred embodiments of this is invention will still fall within the scope of this invention. 
     Furthermore, some of the features of the present invention could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the present invention, and not in limitation thereof.