Browse Prior Art Database

Skip Mask Operation in a No-ID Disk Drive

IP.com Disclosure Number: IPCOM000117789D
Original Publication Date: 1996-Jun-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 155K

Publishing Venue

IBM

Related People

Ching, GR: AUTHOR [+5]

Abstract

The skip mask read/write feature is an enhanced operation of a magnetic disk drive which adds the ability to jump over or skip contiguously numbered sectors without microprocessor intervention. A skip mask is set by the microprocessor, which defines which sectors have associated data transfers. A transfer block count is used to define the total number of "good" data sectors involved, or total number of skip mask bits, in the process. For example, a skip mask of X'55000000' and a transfer block count of 8 means that only the second, the fourth, the sixth, and the eighth non-skip sectors are transferred.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 49% of the total text.

Skip Mask Operation in a No-ID Disk Drive

      The skip mask read/write feature is an enhanced operation of a
magnetic disk drive which adds the ability to jump over or skip
contiguously numbered sectors without microprocessor intervention.  A
skip mask is set by the microprocessor, which defines which sectors
have associated data transfers.  A transfer block count is used to
define the total number of "good" data sectors involved, or total
number of skip mask bits, in the process.  For example, a skip mask
of X'55000000' and a transfer block count of 8 means that only the
second, the fourth, the sixth, and the eighth non-skip sectors are
transferred.

      In a traditional disk drive with ID fields, a skip mask
operation, which is controlled by the disk manager, can be described
as follows:
  1.  A skip mask mode bit is set, which allows the hardware to
select
       a separate control path.
  2.  The skip mask bit is examined by hardware.  If this bit is a
one,
       then the process branches to step 3.  If the skip mask bit is
a
       zero, the transfer block count is decremented and the ID
target
       is incremented.  The next skip mask bit is examined by
hardware
       again at the beginning of the next ID field.  The process is
       repeated until either a skip mask bit of one is found or the
       transfer block count reaches zero; i.e., the operation is
       complete.
  3.  If a bit is set and the ID is valid, a data field read/write
       begins, and the transfer block count is decremented.  If the
ID
       is invalid, the process will wait until a valid ID id
captured.
  4.  At the end of the data field, the expected ID count is
       incremented and the transfer block count is examined.  If the
       transfer block count has reached zero, the operation is
complete.
       Otherwise, the next skip mask bit is examined and the process
       repeats.

      With the ID field removed, as in "headerless" or No-ID (TM)*
disk drives, the disk manager is modified with minor changes to
support normal read/write operations.  However, it can no longer
support skip mask skip operations.

      The present invention integrates hardware control for skip
mask operations into the track mapping implementation described in a
related disclosure (*), to skip the sectors which have associated
skip mask bits of 0.  The skip mask is totally transparent to the
disk manager.

      The invention basically adds a 4-byte skip mask register, a 4
byte shift register, and the associated control logic to the track
mapping implementation described in the previously referenced IBM
disclosure.  The state machine, which is used to determine which
sectors should be omitted based on the skipped sector list in the
track mapping implementation, is modified to have another role, i.e.,
to determine which sectors should have associat...