Method and apparatus for transferring data between a host processor and a data storage device
First Claim
1. A method for transferring data having variable length fields which are separated by fixed time gaps between a host processor and a data storage device wherein error correction bytes are encoded into or decoded from the data during transfer, the method comprising the steps of:
- determining the actual length of the field to be transferred;
computing the number of error correction bytes for the field being transferred;
initiating transfer of the field at the termination of the fixed time gap and before said computation has been completed if the determined actual field length is greater than a predetermined value; and
completing transfer of the field when said computation has been completed.
1 Assignment
0 Petitions
Accused Products
Abstract
In a data processing system in which two-level error correction is performed on variable length data being transferred between the host processor and the data storage device, the logical length of the data being transferred is computed during a fixed time gap with computation continuing after termination of the fixed time gap and commencement of the data transfer. The computation required for the logical length of the data field to accommodate two-level ECC is accomplished by first comparing the actual field length with a value predetermined by the subblock length of the two-level ECC. If the actual length is greater than the predetermined value, then a value equal to the subblock length plus first level ECC bytes is loaded into a counter which begins decrementing at the termination of the fixed time gap so as to synhronize by the byte-by-byte transfer of the data. As the data is being transferred the computation continues. When the computation has been completed, a value equal to the difference between the computed logical length and the subblock length plus first level ECC bytes is loaded into other counters which begin decrementing when the first counter reaches zero. In this manner transfer of the data is not interrupted. This permits two-level ECC to be incorporated into prior data processing systems which utilize a conventional track format with predetermined fixed time gaps, even though such fixed time gaps would otherwise be of insufficient duration to permit computation of the logical length required for two-level ECC.
20 Citations
11 Claims
-
1. A method for transferring data having variable length fields which are separated by fixed time gaps between a host processor and a data storage device wherein error correction bytes are encoded into or decoded from the data during transfer, the method comprising the steps of:
-
determining the actual length of the field to be transferred; computing the number of error correction bytes for the field being transferred; initiating transfer of the field at the termination of the fixed time gap and before said computation has been completed if the determined actual field length is greater than a predetermined value; and completing transfer of the field when said computation has been completed. - View Dependent Claims (2, 3, 4)
-
-
5. A method for transferring variable length data fields between a host processor and a disk file wherein two-level error correction is encoded into or decoded from the fields during transfer of the fields, the method comprising the steps of:
-
determining the actual length of the field to be transferred; computing the number of subblocks within the field; computing the number of error correction bytes required at the subblock and field levels; initiating transfer of the field before computation of the number of required correction bytes is completed if the determined actual field length is greater than a predetermined value; and completing transfer of the field when the error correction byte computation has been completed. - View Dependent Claims (6, 7)
-
-
8. In an apparatus for the transfer of information of variable field length between a host processor and a data recording disk file wherein multiple-level error correction encoding and decoding of the fields into subblocks during transfer requires that the logical length of the fields be calculated during fixed time gaps between successive fields, an improvement comprising:
-
means coupled to the information transfer apparatus for reading the length of the field to be transferred at the end of the fixed time gap; means for computing the number of subblocks in the field whose length has been read during the fixed time gap and for computing the logical length of the field required for error correction; means for comparing the length of the field read with a predetermined value; a first counter coupled to the computing means for receiving a fixed value related to the predetermined value from the computing means and for initiating transfer of the field before computation of the logical length has been completed by the computing means; and a second counter coupled to the computing means for completing the transfer of the field when the first counting means has terminated the count of the fixed value. - View Dependent Claims (9, 10, 11)
-
Specification