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Use of Jumplists to Eliminate Multiple Downstream Load Levels

IP.com Disclosure Number: IPCOM000049068D
Original Publication Date: 1982-May-01
Included in the Prior Art Database: 2005-Feb-09

Publishing Venue

IBM

Related People

Authors:
Winn, GCE [+details]

Abstract

Typically a microprocessor-controlled device, such as a display terminal, may support some function in read only storage (ROS) microcode. Downstream Load is a means by which an extra function is provided by loading additional microcode into random-access memory (RAM) from an upstream node. In order to invoke the Downsteam Loaded microcode, hooks are required at appropriate points in the ROS. These hooks access routines via a Jumplist held in RAM. A Jumplist is simply a contiguous list of JUMP instructions. On a device that has not been Downstream Loaded, this Jumplist will contain data copied from ROS at power on initialization time and will point to ROS routines (which in some cases may be no ops).