Browse Prior Art Database

Emulation-Mode Diagnostic Facility

IP.com Disclosure Number: IPCOM000042394D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Sibbers, DE: AUTHOR

Abstract

In the environment of device input/output (I/O) control, implementation of the device diagnostic package causes problems due to the error recovery and posting procedures implemented by the system and the controller. While adequate for normal operation, the error recovery tends to cause secondary effects resulting in inconsistent fault diagnosis. For buffered I/O controllers one solution to this problem is to use the record buffer area to execute microcode. In controllers where the buffer area is not part of the control store address space, some other means to use the buffer area may be required. This can be resolved by implementing an emulation mode in the base microcode. The emulator then fetches instructions from the record buffer and decodes and executes the instruction.

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Emulation-Mode Diagnostic Facility

In the environment of device input/output (I/O) control, implementation of the device diagnostic package causes problems due to the error recovery and posting procedures implemented by the system and the controller. While adequate for normal operation, the error recovery tends to cause secondary effects resulting in inconsistent fault diagnosis. For buffered I/O controllers one solution to this problem is to use the record buffer area to execute microcode. In controllers where the buffer area is not part of the control store address space, some other means to use the buffer area may be required. This can be resolved by implementing an emulation mode in the base microcode. The emulator then fetches instructions from the record buffer and decodes and executes the instruction. If the emulator emulates the microcode instruction set, then the emulation code has access to all the primary control mechanisms (registers, memory, base microcode). A secondary benefit is that existing microcode support facilities for development can be used with minimum modification. The effective instruction rate is much slower, but this is not critical for most of the diagnostics. For the time critical situations, either linkage is made to the base microcode routines or, in a few instances, special base microcode routines are added. Also, the instruction set may be enhanced, providing useful functions for the diagnostics. The emulator mode is invoked by a command which appea...