HLASM - SSK = Set Storage Key

The opcode of the SSK instruction is X'08'.

Usage

  1. Set the storage key of a page of real storage.

Arguments

  1. Register holding a storage key.
  2. Register containing a page address.

Function

  1. The processor sets the storage key of the 2K or 4K page addressed by the second argument. It is set to the value specified in the low-order byte of the first argument.
  2. The condition code does not change.

Special Cases

  1. If the page address is not a fullword address the instruction fails. The page address does not have to be on a page-boundary, however; any fullword address within a page addresses the page in its entirety.

Related Instructions

  1. ISK was intended to obtain storage keys.
  2. SSKE is now used to set the storage key of a page of real storage.

Hardware

  1. The SSK instruction was part of the original S/360 instruction set. However, it is no longer supported; it has been replaced by the SSKE instruction. Support for the ISK instruction has been dropped when the 370/XA architecture was introduced.

Remarks

  1. Independent of Amode or DAT, the page address is always a 24-bit real address.
  2. The storage key was taken from the low-order 8 bits of the 32-bit register specified as the second argument in the following format:
    1. The first 4 bits (0 through 3) were the actual storage key.
    2. If fetch protect was installed (an optional feature on early machines), the fetch-protect bit was taken from bit 4.
    3. If DAT was installed the Change and Reference bits were taken from bits 5 and 6. I don't know in which order.
  3. Initially the SSK instruction worked on 2K pages only. When 4K pages were introduced, the SSK instruction was modified to address either a 2K page or a 4K page, depending on the address specified and the way that specific page was configured.

Examples

Not available (yet).

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