One of the most important problems that appear during operation of any electronic systems is possibility to store log messages (LOG) and back them up in the case of power loss (further “power down event”). These log messages can help to investigate the reason why the electronic system failure happened and help avoid future failure conditions.
Many systems include storage devices like hard drives, flash cards etc. These devices can store log information during electronic system operation and store this information in the case of a power failure. But some embedded system like “set-up boxes” that are very critical to the cost, to the mechanical size and designed to work stand-alone without human supervision do not have hard drives or writable flash to store log information. In these systems log information is usually located in SRAM during its operation and can not be restored after a power failure. This problem for the embedded systems can be solved by using an additional electronic device that carries out the backup function. In case that power of the main apparatus fails, the backup device stores all LOG information in the internal non-volatile memory by using its internal power source.
The batteries and the capacitors are used in backup devices as the internal power source. Difficulties using batteries are widely known, but also capacitors (and especially super capacitors) that have replaced batteries are not free from shortcomings. Their electrical characteristics can vary under the influence of external factors: humidity and temperatures as well as during lifetime. This leads to the fact that the value of the accumulated charge will be uncertain, especially, if a charge time is limited. The charge time depends on the capacitance of the capacitor and on the diverted current of the external power source. In most cases backup devices use the main power source of the embedded system. But in case when backup device is made as an external device the interface between embedded system (like RS232 serial interface) and backup device is used as the external power source for the backup device. In the case of RS232, the interface has no dedicated power lines and the problem of accumulating charge becomes very important.
Backup devices use accumulated charge for saving LOG information in non-volatile memory. The value of accumulated charge defines the size of the backup information that can be written.
None of the known backup devices can backup LOG information in case the value of accumulated charge is unpredictable. Because existing backup devices may not complete the backup process, therefore the restore process after this will also be unpredictable. It is very important for the backup system to have the information about the exact size of the LOG information that was backed up.
There are many patents concerning the backup process, but none of them solve the previously discussed problem.
Some of the proposals are described in the US Pat. App. 20050283648 by Ashore [1], in the US Pat. App. 20060015683 by Ashore [2], in the US Pat. App. 20060080515 by Spiers et al. [3] etc.
In US Pat Appl. 20050283648 Ashmore offers a back-up RAID controller using the back-up battery of the reserve power supply that is coupled to main power source for charging.
In following US Pat Appl. 20060015683 Ashmore describes a write-caching redundant array of disks (RAID) and offers advantage back-up RAID controller that includes main CPU and additional faster memory controller that is capable of performing the flush operation of the write-posted data. The memory controller is coupled to the volatile memory and the non-volatile memory. This RAID controller uses the main power source and a secondary power source, for example, a capacitor charged by main power source. In the case if the power source fails the CPU is excluded from receiving main power supply, the memory controller performs necessary operations and the secondary power source, for example, capacitor is used only for providing power to the memory controller and two memories.
Several Patent Applications offered by J. Dorny US Pat. Appl. 20040073388 [4], 20050144356 [5] and 20050149663 [6] describe a logger and a method for its use. Computerized method for data loggers according to last Application U.S. Pat. 20050149663 offers a method for estimating the remaining energy capacity of a battery while the battery is powering a digital processor system. The offered method comprises: selecting a predetermined battery consumption characteristics for a particular processor activity.
Spiers et al. [3] US Pat. Appl. 20060080515 proposes a data storage system including a primary data storage device and a backup data storage device. It proposes a data storage system including a primary data storage device and a backup data storage device. The backup data storage device includes a power source, for example, capacitor, battery, or any suitable power source. Said storage system uses a overwriting of the data from volatile memory to non-volatile memory. But the problem related to the value of accumulated charge is nowhere considered.
Present invention focuses on solving the problem related to guarantied backup information in backup devices with an unpredictable value of accumulated charge.