Browse Prior Art Database

Dynamic Sharing of Writeable Control Store

IP.com Disclosure Number: IPCOM000086761D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Frye, HE: AUTHOR

Abstract

Part of the control store of the IBM 370/168 is writeable and can be written dynamically by use of the load microprogram (LMP) instruction. The LMP instruction will load up to four words of control store at a time.

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Dynamic Sharing of Writeable Control Store

Part of the control store of the IBM 370/168 is writeable and can be written dynamically by use of the load microprogram (LMP) instruction. The LMP instruction will load up to four words of control store at a time.

The writeable control store (WCS) of the IBM 370/168 allows the microcoding of relatively complex instructions, such as the DIL instruction of an integrated emulator. Once such an instruction is coded and is utilized in an emulator, which can be invoked interactively via terminals, one must be very careful in modifying this microcode. Such modifications may be required in order to correct errors in the code or to provide enhancements. A simple and convenient method of making such changes is described with reference to Figs. 1 and 2.

When the DIL instruction is loaded, only a few unused words of WCS remain. Some of these words are used to microcode a relatively simple instruction called DILB which branches to an address contained in a floating point register.

The I unit branches to a fixed control store address for each instruction. Suppose this address is 1208 for DIL and 1209 for DILB. In order to test new microcode for DIL, first the contents of words 1208 and 1209 are swapped in WCS. (The contents of each word include the next address.) Thus. any program issuing the DIL instruction will actually get the DILB instruction, and vice versa.

Special software code is provided in the emulator so that any time the...