Browse Prior Art Database

Microcode Patch Method

IP.com Disclosure Number: IPCOM000044370D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Roop, DA: AUTHOR [+2]

Abstract

The patch method uses a custom decode PROM (programmable read-only memory) to generate ROS (read-only storage) disables and enables or patch storage enables and disables. The method enables microcode to be patched, that is, to substitute new microcode for old microcode in small sections without replacing entire ROS modules. The size of the decode PROM is dependent on granularity required. For example, an 8 x 256 bipolar PROM would enable 64K bytes of ROS to be divided into 256 different patch areas. Each patch area would cover 256 bytes. If less granularity is required, a smaller PROM can be used (an 8 x 128 PROM would allow 128 patch areas to cover 512 bytes).

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Microcode Patch Method

The patch method uses a custom decode PROM (programmable read-only memory) to generate ROS (read-only storage) disables and enables or patch storage enables and disables. The method enables microcode to be patched, that is, to substitute new microcode for old microcode in small sections without replacing entire ROS modules. The size of the decode PROM is dependent on granularity required. For example, an 8 x 256 bipolar PROM would enable 64K bytes of ROS to be divided into 256 different patch areas. Each patch area would cover 256 bytes. If less granularity is required, a smaller PROM can be used (an 8 x 128 PROM would allow 128 patch areas to cover 512 bytes). Code words contained in the Decode PROM would be used to enable the patch source and disable ROS (the most significant bit output by the Decode PROM could be used for this purpose). These code words would now be combined with the lower portion of the address bus to form an address input into a patch source. In the patch source, the corrected portion of microcode is stored in the area pointed to by the Decode PROM. As an example, consider the figure. Code resides in ROS 10 of MPU 11 from Address X'0000' to X'FFFF', and microcode residing at Address X'C098' to X'C176' must be changed. Because patches can be 256 bytes long and must begin and end on 256-byte boundaries, as defined by the Decode PROM 12, this patch uses two patch areas. The Decode PROM 12 contains 254 blank words and two patch decod...