Read only store as part of cache store for storing frequently used millicode instructions

US5625808A · kind A · utility

Assignee

• International Business Machines Corporation · US

Inventors

• Charles F. Webb · Wappingers Falls, US
• Mark S. Farrell · Pleasant Valley, US
• Barry W. Krumm · Poughkeepsie, US
• John S. Liptay · Rhinebeck, US
• Jennifer Serena Almoradie Navarro · Poughkeepsie, US
• Steven Risch · Poughkeepsie, US
• Mark A. Check · Hopewell Junction, US

Key dates

• Filing date: May 31, 1995
• Grant date: Apr 29, 1997
• Expiry date: May 31, 2015

Classification

• Technology area (CPC G): Physics
• CPC primary: G06F9/3017
• WIPO field: Computer technology
• WIPO sector: Electrical engineering

Abstract

A read only storage (ROS) array holds a small set of relatively simple millicode instructions; those millicode instruction routines which are most commonly called on in executing common application workloads. The millicode read only store is implemented as a portion of hardware system area (HSA) storage. The cache control includes a register which contains hardware system area address corresponding to the read only store address. When an instruction fetch request is received by the cache control, the absolute address of the instruction fetch request is compared with the read only store address in the register in parallel with the normal cache directory lookup. If the instruction fetch request matches the read only store address, the fetch is made from the read only store independently of the directory lookup result.