Abstract: A circuit for counting events occurring between two different clock domains includes a gray code counter having at least two stages. The gray code counter is incremented by the event to be counted. Dual rank synchronizer circuit and delay flip/flops are coupled to the counter. The circuit includes a comparison logic circuit fed by outputs from the dual rank synchronizers and the delay flip/flops to produce an output signal having a binary value corresponding to a number of events that occurred between transitions of the second clock.

Abstract: A method of data transfer in a data processing system having at least one source buffer and at least one destination buffer. The source buffer includes a plurality of data blocks, each data block having an address and being for storage of data including an identifier uniquely identifying that data block. The destination buffer includes a plurality of data blocks corresponding to the data blocks of the source buffer, each destination block having an address and being for storage of data. Each source block identifier is a function of a corresponding destination block address.

Abstract: A new method for overlapping block read events in a disk drive having synchronously sampled data detection channels is presented. In particular, the new method is for overlapping read back processing by real-time and digital signal processing of first and second data blocks from a storage medium. The method includes steps of clocking real-time and digital signal processes by a clock synchronized to the first data block while the first data block is passing by a data transducer head, clocking the digital signal processes for the first data block by an asynchronous clock operating at a nominal data clocking rate after the first data block has passed by the data transducer head and before a clock has synchronized to the second data block following the first data block, and clocking real-time signal processes for the second data block and completing clocking of the digital processes for the first data block by a clock synchronized to the second data block passing by the data transducer head.

Abstract: A technique for verifying a pre-recorded header in a disk drive uses verification history to protect against errors that can cause verification failure. A head number, sector address, and upper track address (track MSB) are read from the disk and compared with corresponding expected values. The results of the 5 most recent comparisons are saved in three 5-bit memories. During each verification, a programmable selection and comparison circuit selects M of the stored indicators and determines whether at least N of them indicate a match. If so, the corresponding field is declared to be correctly verified, so that subsequent reads or writes to data blocks within the corresponding sector are allowed to proceed.