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Bypassing Deferred and Postponed Error Conditions

IP.com Disclosure Number: IPCOM000052997D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Robinson, FL: AUTHOR [+2]

Abstract

Unit checks report peripheral subsystem error conditions at the time of error, at a later time within a chain of channel commands, or during a following or unrelated chain of channel commands. A set of channel commands is described that result in delaying reporting of an earlier detected error condition because reporting the error with the instant command could cause data processing errors. The input/output channel commands outside of the restricted set of commands enables the earlier detected error condition to be reported after completion of the restricted input/output command.

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Bypassing Deferred and Postponed Error Conditions

Unit checks report peripheral subsystem error conditions at the time of error, at a later time within a chain of channel commands, or during a following or unrelated chain of channel commands. A set of channel commands is described that result in delaying reporting of an earlier detected error condition because reporting the error with the instant command could cause data processing errors. The input/output channel commands outside of the restricted set of commands enables the earlier detected error condition to be reported after completion of the restricted input/output command.

Two methods are used in a buffered peripheral subsystem to provide indications of errors that occurred a relatively long time prior to the actual signaling of the error to the attaching host.

A first method is by a deferred Unit Check, i.e., providing the error indication Unit Check at the time of the initiation of a channel program started after a channel program operation relating to the error being reported.

A second method is called Postponed Unit Check, wherein in a channel program of length n (n>l) channel commands, the error pertaining to channel command C1 is actually signaled to the program at the initial status time of channel command C2, C3 or perhaps even C(n1). The error is reported to the host during a later channel command in the same channel program.

The deferred and postponed error indications are normally supplied to a host at any time, to any command from a host. However, there are certain classes of channel commands that a host may receive either Deferred or Postponed Unit Check (error indications) at any time. For such commands a host may not receive error signals for any conditions other than for the particular errors relating to the instant command, because otherwise: A) the host may not be able to retrieve error information other than a statement from the peripheral subsystem in the form of a Unit Check which signifies that an error exists for some as-yet unspecified condition; B) the host may not be able to resolve the earlier error condition because it may be received by an asynchronous process that has no relation to the process that instigated the earlier error; C) the command that should not receive the Deferred/Postponed Unit Check indications is actually working with a separate logical device which happens to possess the same device address as another logical device for which the earlier error applies.

The commands from an exemplary channel command set that may not receive either deferred error indications (Unit Checks) or Postponed error indications are: SENSE, READ BUFFERED LOG, SET PATH GROUP ID (SPGID), SENSE PATH GROUP ID, CONTROL ACCESS, and LOAD DISPLAY.

Here are examples of each of three problem cases that show that the above commands may not transfer Deferred or Postponed error indications.

1) Suppose that the Sense command was subject to interruption by a Deferred U...