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Microprogram Execution Control Using a Two-Wire Serial Console

IP.com Disclosure Number: IPCOM000035782D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 4 page(s) / 101K

Publishing Venue

IBM

Related People

Crandall, DR: AUTHOR [+2]

Abstract

This article describes a technique for use in microprocessors with a built-in single step interrupt which provides limited execution control capabilities through a two-wire serial interface. (Image Omitted)

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 55% of the total text.

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Microprogram Execution Control Using a Two-Wire Serial Console

This article describes a technique for use in microprocessors with a built-in single step interrupt which provides limited execution control capabilities through a two-wire serial interface.

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During the development of a microprocessor-based system or attachment, a microprocessor development system with an in-circuit emulator is normally used. The emulator replaces the actual microprocessor in the circuit and can be used to display and alter registers, I/O ports, and memory locations and to perform execution control functions such as halt-on-address, compare-on-address, tracing, single step, and software breakpoints. These are invaluable debug capabilities for the design engineer.

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After initial development, though, it is quite possible for additional hardware design bugs or microprogram bugs to become evident. These bugs can typically be reproduced only under specific conditions. It is, therefore, sometimes impossible to duplicate the problem in the design laboratory using the development system and in-circuit emulators are generally not suited for portable use, the use of portable engineering consoles has become increasingly useful.

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The traditional engineering debug approach requires two consoles, a two- wire serial console and a multi-wire execution control console. The multi-wire console may interfere with the circuit under test and therefore may be unusable. If usable, the circuit will probably have to be powered off prior to connecting the console. Sometimes this is undesirable because it may take some time to recreate the situation in which the microcode bug occurs. The technique disclosed herein solves these problems by providing limited execution control capabilities through the two-wire serial interface. It is applicable to designs using microprocessors with a built-in single-step interrupt.

Fig. 1 is a flow chart of the microcode main loop. Fig. 2 is a flow chart of the console mode subroutine. Implementation proceeds in the following manner. After communication is established over the two-wire serial interface (see Figs. 1 and 2), the console conveys a halt address to the microprocessor. The microprocessor stores this address in its memory, enables its single-step interrupt, then continues normal execution. After each normal instruction the microprocessor will be interrupted into the single-step interrupt service routine (see Fig. 3) where it will compare the current instruction address with the stored address. If the address has not been reached, the micro...