Error correcting apparatus

Decoding apparatus for use in error detecting circuitry which encodes a digital data stream by breaking the stream up into predetermined data blocks and inserting after each data block a parity word computed from data bits in the stream to form an encoded stream of codewords, each codeword consisting of an associated parity word and data block, said decoding apparatus comprising,

• means responsive to said encoded stream of codewords for temporarily storing a number of codeword bits equal to the length of a codeword;
• means responsive to said temporarily-stored bits for computing a mathematical function having a value which indicates whether said bits in said storage constitute a codeword or not;
• means responsive to said function value for adding an additional bit to said storage bits if said storage bits do not constitute a code word;
• means responsive to said value for removing the first bit stored in said storage means if said mathematical function indicates that said stored bits do not constitute a codeword;
• and
• means for removing the effect of said last-removed bit from said mathematical function whereby a new mathematical function is generated corresponding to the bits then stored in said storage means.

Apparatus for correcting skew errors in a system for processing parallel streams of digital information wherein, prior to processing, error correction codes are computed from portions of said information in each stream and periodically inserted into the corresponding stream, said apparatus comprising

• means responsive to each processed stream of information for detecting the position in said stream of an error correcting code,
• means for generating a synchronizing signal associated with an information stream when an error correcting code is detected in that stream,
• storage means associated with each stream for temporarily storing processed information in the associated stream when a synchronizing signal is generated for that stream, and
• means for simultaneously reading information out of all of said storage means when synchronizing signals have been detected for all information streams.

Synchronizing apparatus for use in a digital information processing system wherein a stream of digital data bits is broken into a plurality of sequenced parallel bit streams to be processed simultaneously by said data processing system, and the digital data in each of said parallel streams is divided into blocks of predetermined bit length;

• said synchronizing apparatus comprising,
• means, operable prior to processing, for periodically inserting a coded information block computed from bit values in said data blocks into each bit stream,
• means responsive to each processed data bit stream for detecting a coded information block in each stream,
• means responsive to the detection of a coded information block in a processed data bit stream for temporarily storing portions of the associated stream, and
• means responsive to the detection of a coded information block on every one of said processed data streams for simultaneously reading data bits out of said storage means.

Skew correction apparatus for use in a digital information processing system wherein a time sequence of digital data bits is broken into a plurality of parallel bit streams to be processed simultaneously by said data processing system, and wherein, prior to processing, said data in each of said streams is divided into blocks of predetermined bit length, and error correction code bits are computed from the data in each of said blocks and inserted into said stream adjacent to said corresponding block to form a stream of codeword bits, said correction apparatus comprising,

• means for examining a fixed bit length section of each processed stream of codewords and, responsive to the occurrence of a codeword in said section, for generating a synchronizing signal associated with said data stream,
• means responsive to each synchronizing signal for temporarily storing processed data in the corresponding stream;
• and
• means responsive to the generation of synchronizing signals associated with every one of said encoded data streams for simultaneously reading data out of said storage means for each data stream.

A method for correcting skew errors in a digital information processing system wherein a time sequence of digital data blocks is broken into a plurality of parallel streams to be processed simultaneously by said data processing system, and wherein, prior to processing, an error correction code is computed from the data in each of said blocks and inserted into said stream adjacent to said corresponding block to form a stream of codewords, said method comprising the steps of:

• A. continuously examining a section of each processed code word stream,
• B. generating a synchronizing signal associated with said data stream when a codeword is detected in said section,
• C. temporarily storing processed codewords in a stream when a synchronizing signal is generated for that stream, and
• D. simultaneously reading data out of said storage means for each codeword stream when synchronizing signals have been detected for all codeword streams.

Skew correction apparatus for use in a digital multi-track magnetic tape system in which the data recorded on each tape track is divided into blocks of predetermined length and an error correcting code, computed from the values of the bits in each data block, is inserted after the block to form a track of codewords, each codeword consisting of a data block and associated error correcting code pattern, said correction apparatus comprising,

• a first-in first-out buffer store associated with each track,
• means for continuously shifting codeword bits recorded on the associated track into said buffer store,
• means for continuously shifting codeword bits out of said buffer store,
• means, associated with each buffer store and responsive to the presence of bits constituting an entire codeword in said buffer store for generating a synchronizing signal for the associated track,
• means responsive to a synchronizing signal for disabling said shifting out means to temporarily store data recorded on a track in the associated buffer store, and
• means responsive to the generation of synchronizing signals associated with every track for simultaneously shifting data out of each buffer store so that track-to-track skew is eliminated.

Apparatus for detecting an occurrence of a predetermined data bit pattern in a stream of digital data bits, said apparatus comprising,

• means for simultaneously detecting the values of bits in a set of bits having a fixed number of bits in said stream,
• means for computing a mathematical function from said bit values which function has a first value when the set comprises said pattern and a second value when the set does not comprise said pattern,
• means responsive to said second function value for replacing the value of at least one bit in said set with the value of a bit which is not included in said set of bits, and
• means for correcting said function to account for the the value of the replaced one bit.

Decoding apparatus for use in a digital multi-track magnetic tape system in which the data recorded on each tape track is divided into blocks of predetermined length and an error correcting code, computed from the values of the bits in each data block, is inserted after the block to form a stream of codewords, each codeword consisting of a data block and associated error correcting code pattern, said decoding apparatus comprising,

• means responsive to data recorded on a track for temporarily storing a number of bits equal to the length of a codeword,
• means responsive to said temporarily stored bits for computing a mathematical function having a value which indicates whether said bits in said storage constitute a codeword or not,
• means responsive to said function value for adding an additional bit to said storage bits if said storage bits do not constitute a codeword,
• means responsive to said function value for removing one bit stored in said storage means if said value indicates that said stored bits do not constitute a codeword, and
• means for correcting said mathematical function to remove the effect of said last-removed bit from said storage means whereby a new mathematical function is generated corresponding to the bits then stored in said storage means.