Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
1999-04-29
2001-07-17
Le, Dieu-Minh (Department: 2184)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C714S014000, C714S024000, C713S340000
Reexamination Certificate
active
06263453
ABSTRACT:
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.
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Apple Computer Inc.
Carr & Ferrell LLP
Le Dieu-Minh
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