Patent Application
20070094569
This invention relates generally to memory design. More particularly, this invention relates to determining whether errors in memory are soft errors or hard errors.
High-energy neutrons lose energy in materials mainly through collisions with silicon nuclei that lead to a chain of secondary reactions. These reactions deposit a dense track of electron-hole pairs as they pass through a p-n junction. Some of the deposited charge will recombine, and some will be collected at the junction contacts. When a particle strikes a sensitive region of a latch, the charge that accumulates could exceed the minimum charge that is needed to “flip” the value stored on the latch, resulting in a soft error.
The smallest charge that results in a soft error is called the critical charge of the latch. The rate at which soft errors occur (SER) is typically expressed in terms of failures in time (FIT).
A common source of soft errors are alpha particles which may be emitted by trace amounts of radioactive isotopes present in packing materials of integrated circuits. “Bump” material used in flip-chip packaging techniques has also been identified as a possible source of alpha particles.
Other sources of soft errors include high-energy cosmic rays and solar particles. High-energy cosmic rays and solar particles react with the upper atmosphere generating high-energy protons and neutrons that shower to the earth. Neutrons can be particularly troublesome as they can penetrate most man-made construction (some number of neutrons will pass through five feet of concrete). This effect varies with both latitude and altitude. In London, the effect is two times worse than on the equator. In Denver, Colo. with its mile-high altitude, the effect is three times worse than at sea-level San Francisco. In a commercial airplane, the effect can be 100-800 times worse than at sea-level.
A hard error, also called a repeatable error, consistently returns incorrect data. For example, a bit may be such that it always returns a zero regardless of whether a zero or one is written to it. Hard errors are relatively easy to diagnose because they are consistent and repeatable.
There is a need in the art for a memory controller to identify hard and soft errors in memory devices. An embodiment of this invention identifies hard and soft errors in memory devices.
An embodiment of this invention determines whether errors detected in memory are hard errors or soft errors. Memory includes but is not limited to DRAMs (dynamic random access memory), SRAMs (static random access memory), and latches. A common function performed by memory controllers is scrubbing. One type of scrubbing, among others relevant to this invention, includes “reactive scrubbing.”
One application of reactive scrubbing detects errors in data read from DRAM memory using an error-correction algorithm and then writes back corrected data to the location where errors where detected in the DRAM memory. Error-correction algorithms include but are not limited to Hamming, Reed-Solomon, Reed-Muller, and convolution codes. Current reactive scrubbing techniques do not indicate whether the errors were soft errors or hard errors.
The third step, 104, of this embodiment of determining whether errors are soft errors or hard errors, reads data, one or more bits, from the memory location where corrected data was written. The fourth step, 106, of this embodiment of determining whether errors are soft errors or hard errors, records the location where one or more errors were detected as soft errors, in a register block if the data read in step 3, 104, is correct. The fourth step, 106, of this embodiment of determining whether errors are soft errors or hard errors, records the location where one or more errors were detected as hard errors, in a register block if the data read in step 3, 104, is incorrect.
The memory controller, 202, in one embodiment of the invention in
The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.
