Digital Camera Patent Abstract
A system and method for preventing damage to media files within
a digital camera comprise a power manager for detecting power failures,
an interrupt handler for responsively incrementing a counter device
and a removable memory driver for performing memory access operations,
evaluating the counter device to determine whether a power failure
has occurred during the memory access operation and for repeating
the memory access operation whenever a power failure has occurred
during the memory access operation. Digital Camera Patent Claims
What is claimed is:
1. A system for preventing damage to media files within a digital
camera, comprising:
a power manager for detecting a power failure in said digital camera;
an interrupt handler for responsively incrementing a powerfail
counter for incrementally recording the number of instances of power
failure following said power failure; and
a memory driver for performing a memory access operation and subsequently
evaluating said powerfail counter to determine whether said power
failure occurred during said memory access operation;
said memory driver repeating said memory access operation whenever
said memory driver determines that said power failure occurred during
said memory access operation.
2. The system of claim 1 wherein said memory driver:
evaluates said powerfail counter prior to performing said memory
access operation to obtain a pre-operation value;
evaluates said powerfail counter subsequent to performing said
memory access operation to obtain a post-operation value;
compares said pre-operation value and said post-operation value;
and
repeats said memory access operation if said memory driver determines
that said pre-operation value and said post-operation value are
different.
3. The system of claim 1 wherein said interrupt handler registers
selected service routines and transmits a notification of said power
failure to said registered service routines.
4. The system of claim 1 wherein a processor performs a powerdown
sequence to preserve said media files within said digital camera
when a power failure is detected.
5. The system of claim 1 further comprising a voltage sensor for
monitoring a power supply to provide said power manager with the
power supply voltage value.
6. A method for preventing damage to media files within a digital
camera, comprising the steps of:
detecting a power failure within said digital camera;
incrementing a powerfail counter for incrementally recording the
number of instances of power failure in response to said power failure;
evaluating said powerfail counter before and after performing a
memory access operation to determine whether said power failure
occurred during said memory access operation; and
repeating said memory access operation whenever said evaluating
step determines that said power failure occurred during said memory
access operation.
7. The method of claim 6 wherein the steps of evaluating and repeating
further include the steps of:
evaluating said powerfail counter prior to performing said memory
access operation to obtain a pre-operation value;
evaluating said powerfail counter subsequent to performing said
memory access operation to obtain a post-operation value;
comparing said pre-operation value and said post-operation value;
and
repeating said memory access operation if said memory driver determines
that said pre-operation value and said post-operation value are
different.
8. The method of claim 6 further comprising the steps of registering
service routines and transmitting a notification of said power failure
to said registered service routines using an interrupt handler.
9. The method of claim 6 further comprising the steps of performing
a powerdown sequence to preserve said media files within said digital
camera when a power failure is detected, whereby data within said
digital camera is protected.
10. The method of claim 6 further comprising the steps of monitoring
a power supply and responsively providing the power supply voltage
value using a voltage sensor.
11. A computer-readable medium comprising program instructions
for preventing damage to media files within a digital camera by
performing the steps of:
detecting a power failure within said digital camera;
incrementing a powerfail counter for incrementally recording the
number of instances of power failure in response to said power failure;
evaluating said powerfail counter before and after performing a
memory access operation to determine whether said power failure
occurred during said memory access operation; and
repeating said memory access operation whenever said evaluating
step determines that said power failure occurred during said memory
access operation.
12. The computer-readable medium of claim 11 wherein the steps
of evaluating and repeating further include the steps of:
evaluating said powerfail counter prior to performing said memory
access operation to obtain a pre-operation value;
evaluating said powerfail counter subsequent to performing said
memory access operation to obtain a post-operation value;
comparing said pre-operation value and said post-operation value;
and
repeating said memory access operation if said memory driver determines
that said pre-operation value and said post-operation value are
different.
13. The computer-readable medium of claim 11 further comprising
the steps of registering service routines and transmitting a notification
of said power failure to said registered service routines using
a interrupt handler.
14. The computer-readable medium of claim 11 further comprising
the steps of performing a powerdown sequence and a subsequent restart
sequence after detecting said power failure, whereby said media
files within said digital camera are protected.
15. The computer-readable medium of claim 11 further comprising
the steps of monitoring a power supply and responsively providing
the power supply voltage value using a voltage sensor.
16. A system for preventing damage to media files within a digital
camera, comprising:
means for detecting a power failure within said digital camera;
means for incrementing a powerfail counter for incrementally recording
instances of power failure in response to said power failure;
means for evaluating said powerfail counter before and after performing
a memory access operation to determine whether said power failure
occurred during said memory access operation; and
means for repeating said memory access operation whenever said
means for evaluating determines that said power failure occurred
during said memory access operation.
17. The system of claim 16 wherein said means for evaluating and
repeating further include means for:
evaluating said powerfail counter prior to performing said memory
access operation to obtain a pre-operation value;
evaluating said powerfail counter subsequent to performing said
memory access operation to obtain a post-operation value; comparing
said pre-operation value and said post-operation value; and
repeating said memory access operation if said memory driver determines
that said pre-operation value and said post-operation value are
different.
18. The system of claim 16 further comprising means for registering
service routines and transmitting a notification of said power failure
to said means for registering service routines.
19. The system of claim 16 further comprising the means for performing
a powerdown sequence and a subsequent restart sequence after detecting
said power failure, whereby said media files within said digital
camera are protected.
20. The system of claim 16 further comprising means for monitoring
a power supply and responsively providing the power supply voltage
value using a voltage sensor.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to digital cameras and more particularly
to a system and method for preventing power failure damage to media
files within a digital camera device.
2. Description of the Background Art
Modern photographic technology presently includes a variety of
digital camera devices which capture image data by electronically
scanning selected target objects. Digital camera devices often process
and compress the captured image data before storing the processed
image data into internal or external memory devices. These memory
devices typically include various types of nonvolatile memory which
are accessed in read/write operations that store and access captured
image data.
Protecting the captured image data during the memory access operations
is an important consideration of both camera manufacturers and camera
users. Camera designers must therefore anticipate the occurrence
of any events which might endanger the integrity of the captured
image data.
A power failure during a memory read/write operation within a digital
camera device is one example of an event which might seriously jeopardize
image data. For example, the digital camera may be accessing a file,
rewriting a file directory or rewriting a file allocation table
at the time a power failure occurs. The intervening power failure
may prevent the successful completion of the memory access operation
and thus damage integrity of the image data.
Further, a power failure may interrupt various camera memory functions
which typically resume their respective tasks whenever power is
restored to the digital camera. The interrupted functions, however,
would be unaware that a power failure had intervened. The interrupted
memory functions would thus be unaware of the hardware reset which
results from reapplying power after the power failure. This confusion
between the system software and hardware would potentially endanger
camera operations. For the foregoing reasons, an improved system
and method is needed for preventing damage to media files within
a digital camera device according to the present invention.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system and method are
disclosed for preventing damage to media files within a digital
camera device. The preferred embodiment of the present invention
includes a central processing unit, a powerfail counter, a removable
memory driver, a first-level interrupt handler, various interrupt
service routines, a power manager and a voltage sensor.
In the preferred embodiment, the first-level interrupt handler
initially sets the powerfail counter to a value of zero. Various
interrupt service routines (each corresponding to a specific camera
function or operation) may register themselves with the first-level
interrupt handler (which coordinates all interrupts within the digital
camera) to receive notification of an intervening power failure.
Alternately, each interrupt service routine may receive a unique
interrupt directly, via some form of vector interrupt mechanism
or by using a hard-coding methodology.
The power manager monitors the voltage sensor to detect a power
failure within the digital camera. After detecting a power failure
in which the camera operating power is less than a specified threshold
value, the power manager generates a powerfail interrupt. The central
processing unit responsively performs a powerfail powerdown sequence
to preserve image data contained within the digital camera at the
time of the intervening power failure. The power manager removes
operating power from all non-critical subsystems and switches the
critical subsystems to a backup power supply. The central processing
unit and the camera's volatile memory are thus maintained in a static
low-power mode, with all states preserved intact.
After the power failure is remedied, the central processing unit
performs a restart sequence to preserve any stored image data and
to return the digital camera to a normal operational mode. In the
preferred embodiment, the first-level interrupt handler increments
the powerfail counter to record the intervening power failure. The
first level interrupt handler then notifies the registered interrupt
service routines about the power failure restart and corresponding
hardware reset.
In alternate embodiments, the interrupt service routines may operate
in cooperation with various other system routines. These cooperating
routines thus may form various hierarchical networks which operate
in synchronous or asynchronous modes. For example, a particular
interrupt service routine may function in response to a device driver.
The device driver, in turn, may function in response to an application
program. In such cases, the interrupt service routines typically
propagate their received power failure notification to any related
routines in the network which require notification of the power
failure restart.
In the normal operational mode, the digital camera periodically
performs a memory access operation which requires successful completion.
To ensure that a memory access operation is completed without an
intervening power failure, the removable memory driver preferably
reads the powerfail counter prior to performing a memory access
operation to obtain a pre-operation value. After performing the
memory access operation, the removable memory driver again reads
the powerfail counter to obtain a post-operation value. The removable
memory driver then compares the pre-operation value and the post-operation
value, and repeats the memory access operation if the pre-operation
value and the post-operation value are different. The present invention
thus preserves the integrity of captured image data and effectively
prevents damage to media files in the digital camera device.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a digital camera according to the
present invention;
FIG. 2 is a block diagram of the preferred embodiment for the imaging
device of FIG. 1;
FIG. 3 is a block diagram of the preferred embodiment for the computer
of FIG. 1;
FIG. 4 is a block diagram showing the preferred embodiment of the
Read-Only Memory of FIG. 3;
FIG. 5 is a block diagram showing the preferred embodiment of the
Dynamic Random-Access Memory of FIG. 3;
FIG. 6 is a flowchart of preferred general method steps for recovering
from a power failure according to the present invention;
FIG. 7 is a flowchart of preferred method steps for performing
a powerfail powerdown sequence according to the present invention;
FIG. 8 is a flowchart of preferred method steps for performing
a resume/restart sequence according to the present invention; and
FIG. 9 is a flowchart of preferred method steps for preventing
power failure damage to memory files according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention discloses a system and method for preventing
damage to media files within a digital camera device and comprises
a power manager for detecting power failures, an interrupt handler
for responsively incrementing a counter device and a removable memory
driver for performing memory access operations, evaluating the counter
device to determine whether a power failure has occurred during
the memory access operation and for repeating the memory access
operation whenever a power failure has occurred during the memory
access operation.
Referring now to FIG. 1, a block diagram of a camera 110 is shown
according to the present invention. Camera 110 preferably comprises
an imaging device 114, a system bus 116 and a computer 118. Imaging
device 114 is optically coupled to an object 112 and electrically
coupled via system bus 116 to computer 118. Once a photographer
has focused imaging device 114 on object 112 and, using a capture
button or some other means, instructed camera 110 to capture an
image of object 112, computer 118 commands imaging device 114 via
system bus 116 to capture raw image data representing object 112.
The captured raw image data is transferred over system bus 116 to
computer 118 which performs various image processing functions on
the image data before storing it in its internal memory. System
bus 116 also passes various status and control signals between imaging
device 114 and computer 118.
Referring now to FIG. 2, a block diagram of the preferred embodiment
of imaging device 114 is shown. Imaging device 114 preferably comprises
a lens 220 having an iris, a filter 222, an image sensor 224, a
timing generator 226, an analog signal processor (ASP) 228, an analog-to-digital
(A/D) converter 230, an interface 232, and one or more motors 234.
U.S. Pat. No. 5,496,106, entitled "A System and Method For
Generating a Contrast Overlay as a Focus Assist for an Imaging Device,"
issued on Mar. 5, 1966, is incorporated herein by reference, and
provides a detailed discussion of the preferred elements of imaging
device 114. Briefly, imaging device 114 captures an image of object
112 via reflected light impacting image sensor 224 along optical
path 236. Image sensor 224 responsively generates a set of raw image
data representing the captured image 112. The raw image data is
then routed through ASP 228, A/D converter 230 and interface 232.
Interface 232 has outputs for controlling ASP 228, motors 234 and
timing generator 226. From interface 232, the raw image data passes
over system bus 116 to computer 118.
Referring now to FIG. 3, a block diagram of the preferred embodiment
for computer 118 is shown. System bus 116 provides connection paths
between imaging device 114, power manager 342, central processing
unit (CPU) 344, dynamic random-access memory (DRAM) 346, input/output
interface (I/O) 348, read-only memory (ROM) 350, and connector 352.
In the preferred embodiment, removable memory 354 may also connect
to system bus 116 via connector 352.
Power manager 342 communicates via line 366 with power supply 356
and coordinates power management operations for camera 110 as discussed
below in conjunction with FIGS. 6-9. CPU 344 typically includes
a conventional processor device for controlling the operation of
camera 110. In the preferred embodiment, CPU 344 is capable of concurrently
running multiple software routines to control the various processes
of camera 110 within a multi-threading environment. DRAM 346 is
a contiguous block of dynamic memory which may be selectively allocated
to various storage functions by computer 118. DRAM 346 includes
a powerfail counter 347 which is incremented each time a power failure
occurs in power supply 356. DRAM 346 and powerfail counter 347 are
further discussed below in conjunction with FIGS. 5-9.
I/O 348 is an interface device allowing communications to and from
computer 118. For example, I/O 348 permits an external host computer
(not shown) to connect to and communicate with computer 118. I/O
348 also permits a camera 110 user to communicate with camera 110
via a set of externally-mounted user controls and via an external
LCD display panel. ROM 350 typically comprises a conventional nonvolatile
read-only memory which stores a set of computer-readable program
instructions to control the operation of camera 110. ROM 350 is
further discussed below in conjunction with FIG. 4. Removable memory
354 serves as an additional image data storage area and is preferably
a non-volatile device, readily removable and replaceable by a camera
110 user via connector 352. Thus, a user who possesses several removable
memories 354 may replace a full removable memory 354 with an empty
removable memory 354 to effectively expand the picture-taking capacity
of camera 110. In the preferred embodiment of the present invention,
removable memory 354 is typically implemented using a flash disk.
Power supply 356 supplies operating power to the various components
of camera 110. In the preferred embodiment, power supply 356 provides
operating power to a main power bus 362 and also to a secondary
power bus 364. The main power bus 362 provides power to imaging
device 114, I/O 348, ROM 350 and removable memory 354. The secondary
power bus 364 provides power to power manager 342, CPU 344 and DRAM
346.
Power supply 356 is connected to main batteries 358 and also to
backup batteries 360. In the preferred embodiment, a camera 110
user may also connect power supply 356 to an external power source.
During normal operation of power supply 356, the main batteries
358 provide operating power to power supply 356 which then provides
the operating power to camera 110 via both main power bus 362 and
secondary power bus 364.
During a power failure mode in which the main batteries 358 have
failed (when their output voltage has fallen below a minimum operational
voltage level) the backup batteries 360 provide operating power
to power supply 356 which then provides the operating power only
to the secondary power bus 364 of camera 110. Selected components
of camera 110 (including DRAM 346) are thus protected against a
power failure in the main batteries 358.
Power supply 356 preferably also includes a flywheel capacitor
connected to the power line coming from the main batteries 358.
If the main batteries 358 suddenly fail, the flywheel capacitor
temporarily maintains the voltage from the main batteries 358 at
a sufficient level, so that computer 118 can protect any image data
currently being processed by camera 110 before shutdown occurs.
Voltage sensor 359 detects the voltage supplied by main batteries
358 and responsively provides the detected voltage reading to power
manager 342. The operation of power manager 342, power supply 356
and voltage sensor 359 are further discussed below in conjunction
with FIGS. 6-8.
Referring now to FIG. 4, a memory map showing the preferred embodiment
of read-only memory (ROM) 350 is shown. In the preferred embodiment,
ROM 350 includes control application 400, toolbox 402, drivers 404,
kernel 406 and system configuration 408. Control application 400
comprises program instructions for controlling and coordinating
the various functions of camera 110. Toolbox 402 contains selected
function modules including memory manager 410 which is controlled
by control application 400 and responsively allocates DRAM 346 storage
locations depending upon the needs of computer 118 and the sets
of received image data.
Drivers 404 control various components of camera 110 and include
removable memory driver 411, a first level interrupt handler (FLIH)
412 and various interrupt service routines (ISRs) 414. In the preferred
embodiment, removable memory driver 411 is a routine which controls
and coordinates the operation of removable memory 354. Removable
memory driver 411 is further discussed below in conjunction with
FIG. 9. FLIH 412 is preferably a software routine which coordinates
all interrupts within camera 110. FLIH 412 typically handles ordinary
non-critical interrupts and also handles non-maskable critical interrupts
such as a power failure in main batteries 358. FLIH 412 preferably
communicates with the various ISRs 414 which are each designed to
handle a specific corresponding interrupt within camera 110. FLIH
412 notifies the appropriate ISRs 414 via a "signal" when
the interrupts occur. A signal is a mechanism used by multi-tasking
operating systems for inter-process communications and synchronization.
For example, a camera 110 user may request zoom motor 234 to perform
a zoom operation using lens 220. When the requested zoom process
is complete, an interrupt is generated to indicate that zoom motor
234 and lens 220 have reached their destination positions. The particular
ISR 414 which corresponds to the foregoing zoom process then responsively
handles the generated interrupt and provides a status update to
higher-level routines, if necessary. In preferred embodiment, kernel
406 provides a range of basic underlying services for the camera
110 operating system. System configuration 408 performs initial
start-up routines for camera 110, including the boot routine and
initial system diagnostics.
Referring now to FIG. 5, a memory map showing the preferred embodiment
of dynamic random-access memory (DRAM) 346 is shown. In the preferred
embodiment, DRAM 346 includes working memory 530, RAM disk 532 and
system area 534. Working memory 530 includes a powerfail counter
347, frame buffers 536 (for initially storing sets of raw image
data received from imaging device 114), image processing (IP) buffers
538 (for temporarily storing image data during the image processing
and compression 420 process), and Pfail CountL 540. In the preferred
embodiment, power fail counter 347 stores a value which first-level
interrupt handler 412 preferably increments each time voltage sensor
359 detects a power failure in main batteries 358. Pfail CountL
540 may selectively be used to store a local copy of the current
value of powerfail counter 347, according to the present invention.
Powerfail counter 347 and Pfail CountL 540 are further discussed
below in conjunction with FIGS. 6-9. Working memory 530 may also
contain various stacks, data structures and variables used by CPU
344 while executing the software routines used within computer 118.
RAM disk 532 is a memory area used for storing raw and compressed
image data and typically is organized in a "sectored"
format similar to that of conventional hard disk drives. In the
preferred embodiment, RAM disk 532 uses a well-known and standardized
file system to permit external host computer systems, via I/O 348,
to readily recognize and access the data stored on RAM disk 532.
System area 534 typically stores data regarding system errors (for
example, why a system shutdown occurred) for use by CPU 344 upon
a restart of computer 118.
Referring now to FIG. 6, a flowchart of preferred general method
steps for recovering from a power failure is shown. Initially, a
user applies 640 power to camera 110 by installing main batteries
358 and backup batteries 360, and then activating an externally-mounted
power on-off switch. First-level interrupt handler (FLIH) 412 then
sets 642 powerfail counter 347 to a value of zero. Next, various
interrupt service routines 414 register 644 with the first level
interrupt handler 412 to request notification in the event of a
power failure in main batteries 358.
CPU 344 then runs 646 control application 400 to operate camera
110 in normal operation mode which captures, processes, compresses
and stores sequential sets of image data. In normal operation mode,
CPU 344 periodically requests the execution of various critical
processes. In the preferred embodiment, CPU 344 repeatedly checks
powerfail counter 347 to determine whether a critical process has
been interrupted by an intervening power failure. This process of
using powerfail counter 347 to ensure the successful execution of
critical processes is further discussed below in conjunction with
FIG. 9.
Next, voltage sensor 359 senses 648 the voltage level of main batteries
358 and provides power manager 342 with the sensed voltage level.
Power manager 342 then determines 650 whether the voltage level
of main batteries 358 is greater than a predetermined threshold
voltage level. The threshold value is typically selected to be incrementally
higher that the minimum operating voltage (to permit orderly shutdown
of the camera 110 processes). If the voltage of main batteries 358
is greater than the selected threshold value, then the FIG. 6 process
repeats the steps 646, 648 and 650.
However, if the voltage of main batteries 358 is not greater 650
than the predetermined threshold value, then power manager 342 generates
652 a powerfail interrupt. In the preferred embodiment, the powerfail
interrupt may be disabled in rare cases in which a sequence of CPU
344 instructions must never be interrupted by a power failure. Any
disabling of the powerfail interrupt, however, is restricted to
a very short period of time. Next, CPU 344 receives the generated
powerfail interrupt and responsively performs 654 a powerfail powerdown
sequence to protect the image data currently within camera 110.
The powerfail powerdown sequence is further discussed below in conjunction
with FIG. 7.
The camera 110 user may then replace 655 the main batteries 358
and activate the camera 110 power on/off switch. CPU 344 then performs
656 a restart/resume sequence to bring camera 110 back to normal
operating mode while also preserving any existing image data. FLIH
412 then increments 658 powerfail counter 347 to indicate the occurrence
of a power failure in main batteries 358. Alternately, powerfail
counter 347 may be a hardware register which is incremented in power
manager 342.
The first level interrupt handler 412 then notifies 660 any registered
interrupt service routines 414 about the power failure restart so
that the interrupt service routines 414 are aware that their corresponding
hardware components have been reset by the power failure and the
subsequent camera 110 powerup. The power failure notification allows
the registered interrupt service routines 414 to run depending upon
their relative task priority. Typically, this notification is accomplished
through the use of a signal or semaphore which wakes up the interrupt
service routine.
In alternate embodiments, the interrupt service routines may operate
in cooperation with various other system routines. These cooperating
routines thus may form various hierarchical networks which operate
in synchronous or asynchronous modes. For example, a particular
interrupt service routine may function in response to a device driver.
The device driver, in turn, may function in response to an application
program. In such cases, the interrupt service routines typically
propagate their received power failure notification to any related
routines in the network which require notification of the power
failure restart. Finally, the FIG. 6 process then returns to step
646 and CPU 344 runs control application 400 to operate camera 110
in normal operation mode, as discussed above.
Referring now to FIG. 7, a flowchart of preferred method steps
for performing a powerfail powerdown sequence according to the present
invention is shown. Initially, power manager 342 sets 710 a PFAIL
bit which records the occurrence of a power failure so that computer
118 software routines may subsequently access this information when
needed. Next, power manager 342 turns off 712 all non-critical subsystems.
Power manager 342 then signals 714 CPU 344 with an interrupt and
CPU 344 responsively stops 716 the current process.
Next, CPU 344 sets 718 the RESUME bit in power manager 342 to indicate
that CPU 344 should not be reset in a subsequent powerup of camera
110. CPU 344 then forces 720 a full refresh of DRAM 346 and then
forces 722 DRAM 346 into a self-refresh mode. Next, CPU 344 signals
724 power manager 342 to shut down and then CPU 344 halts 726 operation.
After halting, CPU 344 still receives operating power from backup
batteries 360 and is essentially stopped "in place." In
this static mode, system bus 116 is in a tri-state condition and
the CPU 344 clock is stopped. All CPU 344 states, however, are still
intact (for example, the registers, program counter, cache and stack
are preserved intact) and image data in DRAM 346 is also preserved
intact. Next, power manager 342 removes 728 operating power from
main power bus 362. The FIG. 7 powerfail powerdown sequence is then
complete.
Referring now to FIG. 8, a flowchart of preferred method steps
for performing a restart/resume sequence according to the present
invention is shown. Initially, CPU 344 waits 828 for a "wake
up" signal which is typically generated in response to the
activation of a camera 110 power on-off switch. After the "wake
up" signal is generated, power manager 342 determines 830 whether
power supply 356 is generating enough operating power to start camera
110. If sufficient operating power is present, power manager 342
starts 832 power supply 356 in normal mode with the main batteries
358 providing operating power to power supply 356 which then responsively
provides the operating power to main power bus 362 and also to secondary
power bus 364. Next, power manager 342 determines 834 whether the
generated operating power is maintaining a sufficient voltage level.
If operating power is sufficient in camera 110, power manager 342
then determines 836 whether a RESUME bit has been set in power manager
342. In the preferred embodiment, CPU 344 sets the RESUME bit in
response to a power failure in order to indicate that CPU 344 should
not be reset in a subsequent powerup of camera 110. If the RESUME
bit has been set, power manager 342 restarts 838 the CPU 344 which
responsively resumes 840 normal operation of DRAM 346 and then resumes
842 the camera 110 process which was interrupted by the intervening
power failure.
If the RESUME bit has not been set, then power manager 342 restarts
844 the CPU 344 and issues 846 a CPU 344 reset. CPU 344 then resumes
848 normal operation of DRAM 346 and boots 850 the computer 110
system using the system configuration 408 routine. Next, CPU 344
determines 852 whether a MSAVE bit has been set in power manager
342. In the preferred embodiment, CPU 344 sets the MSAVE bit to
specify that RAM disk 532 contains image data that should be saved
upon restart of computer 118. If the MSAVE bit has not been set,
computer 118 formats 854 a new RAM disk 532. CPU 344 then runs 858
control application 400 for normal operation of camera 110. In step
852, if the MSAVE bit has been set, then CPU 344 recovers and mounts
856 RAM disk 532. CPU 344 then runs 858 control application 400
for normal operation of camera 110. The restart/resume process of
FIG. 8 then ends.
Referring now to FIG. 9, a flowchart of preferred method steps
for preventing power failure damage to the contents of removable
memory 354 is shown. This FIG. 9 process may also be applied to
selected other camera 110 processes or operations whose successful
completion would be seriously impaired by an intervening power failure.
Initially, removable memory driver 411 reads 956 the contents of
powerfail counter 347 to obtain a current PFCount value. Next, removable
memory driver 411 saves 958 a local copy of the current PFCount
value into Pfail CountL 540 within working memory 530. Then, removable
memory driver 411 obtains and decodes 960 any existing requests
to perform a function related to removable memory 411. Next, removable
memory driver 411 determines 962 whether the requested driver 411
function requires accessing removable memory 354 to perform a memory
input/output function, such as a read/write operation.
If the requested memory function does not require an access of
removable memory 354, then removable memory driver 411 performs
964 these non-read/write functions and the FIG. 9 process ends.
However, if the requested memory function involves an input/output
operation to move information to or from removable memory 354, then
removable memory driver 411 performs 966 the read/write operation(s)
as requested. These operations typically include the complementary
steps of sending an input/output command and any related data to
removable memory 354 and subsequently receiving a corresponding
response from removable memory 354.
After removable memory driver 411 has performed the requested read/write
operation, then removable memory driver 411 reads 968 the current
value in powerfail counter 347 to obtain a new current PFCount value.
Next, removable memory driver 411 compares 970 the new current PFCount
value (step 968) and the previously-saved PFCountL 540 value (step
958). Removable memory driver 411 determines 972 whether the new
current PFCount value and the previously-saved PFCountL 540 value
are different.
If the new current PFCount value and the previously-saved PFCountL
value are not different, then the read/write operation to removable
memory 354 was not interrupted by an intervening power failure and
removable memory driver 411 has successfully performed the read/write
function as requested. The FIG. 9 process therefore ends. If, however,
the new current PFCount value and the previously-saved PFCountL
value are different (step 972), then the read/write operation has
been interrupted by an intervening power failure within camera 110.
If a power failure has intervened, then removable memory driver
411 reads 974 the current contents of powerfail counter 347 to obtain
a new current PFCount value and also saves 976 a local copy of the
new current PFCount value into Pfail CountL 540 within working memory
530. In other embodiments, removable memory driver 411 may alternatively
store the new current PFCount value obtained in step 968 into Pfail
CountL 540, providing that the step 970 comparison process does
not alter or destroy the step 968 PFCount value. Removable memory
driver 411 then sets up 978 removable memory 354 for a retry of
the requested read/write operation. For example, removable memory
driver 411 may issue a reset command to removable memory 354 prior
to a retry of the read/write operation. The FIG. 9 process then
loops back to step 966 to retry the read/write operation. Steps
966 through 978 preferably repeat until the new current PFCount
value and the previously-saved PFCountL value (step 972) are equal.
The FIG. 9 process may then terminate, because the requested read/write
operation has been successfully completed without any intervening
power failures.
The invention has been explained above with reference to a preferred
embodiment. Other embodiments will be apparent to those skilled
in the art in light of this disclosure. For example, the powerfail
counter 347 of the present invention may be used to record occurrences
within computer 118 other than the power failure discussed above
in the preferred embodiment. Furthermore, the present invention
may readily be applied to devices other than the removable memory
354 discussed in the preferred embodiment. Therefore, these and
other variations upon the preferred embodiment are intended to be
covered by the present invention, which is limited only by the appended
claims. |