This post supplements that of John McKown.
Paul Gilmartin writes:
What ever became of the guarantee that STCK would return unique values
(subject to clock
wrap)? (Does STCKE make similar assurance?) (Is there any similar
assurance across a sysplex?)
Seriatim, nothing happened to the guarantee that successive STCK
instructions executed by the same CP yield unique values that are in
monotone ascending 'logical' sequence.
The same 'assiurance' is also available for STCKE values, which have the
additional merit that they will not wrap in 2042.
The assurance across a multi-configuration sysplex is a little less
straightforward. It can be provided, but a one-time effort is required to
do so. The full 16-byte STCKE value contains a rightmost two-byte field
(bits 112-127) called the Programmable Field. This value can be set by a
privileged instruction, SCKPF. How to set these values to ensure the
uniquess of STCKE values is then straightforward. Quoting now the
Principles of Operation:
Programming Note: The values in the TOD programmable registers of a
configuration should be
the same and should be unique within a multiple-configuration system.
John Gilmore
Ashland, MA 01721
USA
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