Method and apparatus for calculating the longitudinal redundancy check

Abstract

The invention relates to a method and apparatus for checking data integrity in a data communications system in which plural data streams can be intermixed and wherein the data streams have a frame transmission format in which the frame is different than the logical block length of the data stream components. The integrity of the transmission process is checked without requiring system processor involvement, unless errors are detected. A first incoming data stream, composed of logical blocks, is received; and a running longitudinal redundancy check is calculated. If the data stream is interrupted at other than the end of a block, the intermediate value of the LRC is stored in a context storage associated only with that data stream. When the data stream continues, and this may occur after other data streams have been received, the intermediate value of the LRC is recalled from the context storage and the running longitudinal redundancy check calculation is continued. The storage and calculation steps continue each time the data stream is interrupted other than at a logical termination of a logical block for the data stream. The communications process is particularly applicable to mass storage subsystems in which the data streams are directed to and from the storage media.