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SCSI Raise Overlength Error and Recovery

IP.com Disclosure Number: IPCOM000103975D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Becker, DE: AUTHOR [+4]

Abstract

During an SCSI write operation, a problem exists if a Target device requests more bytes of data than the Initiator is set up to transfer. If the Initiator halts the operation at the point of the extra request and lets an operation timer expire, a significant period of time could be wasted during which other operations to the Target device could have been performed. Or, if the Initiator acknowledges these extra requests with some data pattern that gets written to the Target media, this extra data could corrupt good data already stored in the Target device. Described is an error interrupt, called a Raise Overlength Error, and an error recovery function that is performed in a timely manner by the Initiator when more data is requested from the Initiator than it is ready to acknowledge.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

SCSI Raise Overlength Error and Recovery

      During an SCSI write operation, a problem exists if a Target
device requests more bytes of data than the Initiator is set up to
transfer.  If the Initiator halts the operation at the point of the
extra request and lets an operation timer expire, a significant
period of time could be wasted during which other operations to the
Target device could have been performed.  Or, if the Initiator
acknowledges these extra requests with some data pattern that gets
written to the Target media, this extra data could corrupt good data
already stored in the Target device.  Described is an error
interrupt, called a Raise Overlength Error, and an error recovery
function that is performed in a timely manner by the Initiator when
more data is requested from the Initiator than it is ready to
acknowledge.

      In an SCSI Bus data transfer operation, the transfer length is
placed in a counter in the Initiator that keeps track of the number
of data bytes that the Initiator has transferred during the
operation.  This transfer length is also passed to the Target during
command phase and the Target then places this transfer length in its
own data transfer counter.  During a write operation, the Target
requests and stores data from the Initiator.  If the Target requests
more data than the Initiator is ready to transfer, but the Initiator
continues to acknowledge the Target with data, this additional data
could be written over good data al...