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Extended Diagnostics

IP.com Disclosure Number: IPCOM000042206D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Bradley, DJ: AUTHOR [+3]

Abstract

In certain computer systems, the diagnostic software is packaged in a single file containing a "Diagnostic Control Program", subroutines common to multiple devices and routines specific to individual species of devices. Due to architectural restrictions, these elements have to be contained in a single segment occupying not more than 64K bytes of storage. Therefore, as new devices are added to the system or existing devices are modified, the entire package has to be revised. The expenses and difficulties of such revisions are avoided by the following rearrangement of the diagnostic functions. The processor architecture allows the implementation of this rearrangement through the use of segment registers. A segment is a block of storage of variable size up to 64K bytes.

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Extended Diagnostics

In certain computer systems, the diagnostic software is packaged in a single file containing a "Diagnostic Control Program", subroutines common to multiple devices and routines specific to individual species of devices. Due to architectural restrictions, these elements have to be contained in a single segment occupying not more than 64K bytes of storage. Therefore, as new devices are added to the system or existing devices are modified, the entire package has to be revised. The expenses and difficulties of such revisions are avoided by the following rearrangement of the diagnostic functions. The processor architecture allows the implementation of this rearrangement through the use of segment registers. A segment is a block of storage of variable size up to 64K bytes. The storage area can be divided into multiple segments which begin on 16-byte boundaries. The segment registers serve as pointers to the beginning of a segment. By properly setting the segment register, any byte in the storage area can be accessed. A Modified Diagnostic Control Program (MDCP) and the device diagnostics are separated into discrete files. The MDCP reads each device diagnostic file and places it into sequential storage segments. The MDCP recognizes which files are device diagnostics by the file name extension. The MDCP places each device diagnostic in a separate segment of storage which may be up to 64K bytes in size. If the diagnostic is of lesser size, the MDCP reduces the storage segment size appropriately. The MDCP starts the next diagnostic segment immediately following the diagnostic just loaded. Thus, the total program size is bounded only by the amount of storage in the system. The MDCP contains very little device-dependent information. A header at the beginning of each diagnostic file contains (1) a jump instruction to the entry point for the device diagnostic, (2) a device number defined in the MDCP, and (3) the name of the device. Multiple headers may exist at the beginning of the diagnostic file, allowing one file to function for multiple devices. Each diagnostic is written to execute within its own stora...