M-Systems Flash Disk Pioneers Flash Memory manual Enhanced EDC and ECC

Implementing MLC NAND Flash for Cost-Effective, High-Capacity Memory

Enhanced EDC and ECC

The Error Detection Code (EDC) and Error Correction Code (ECC) developed for x2 technology is based on M-Systems’ highly effective combination used in previous generation DiskOnChip products. This system contains hardware-embedded EDC mechanism to detect errors on-the-fly and software-embedded ECC mechanism to reduce silicon size and cost. The combination of hardware and software results in the industry’s most cost-effective data reliability for Binary flash. It corrects at least 2 errors per page without imposing performance penalties.

The EDC and ECC enhancements for MLC are capable of correcting up to 4 errors per page, using two industry-standard error codes: an extended Hamming code and a BCH (Bose, Chaudhuri and Hocquenghem) code.

The Hamming code can detect 2 errors per page and correct 1 error per page. The BCH code can detect 4 errors per page and correct an equal number, with a safety margin that enables it to detect 5 errors per page with a probability of 99.9 percent. This combination of codes provides an even higher rate of coverage than 2 bits per page provide for Binary flash technology.

It also ensures that the minimal amount of code required is used for detection and correction to deliver the required reliability without degrading performance. The entire thin controller occupies less than 5 percent of the die size for a 512Mbit device, of which only 15 percent is used for the EDC circuit to provide exceptional detection capabilities.

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