Cyrix Corporation

Via-cyrix, Inc.

William C Patton

Mark W Bluhm

Mark W Hervin

Thomas D Selgas

Thomas B Brightman

Stanley D Harder

A circuit for diagnosing and debugging a processor for executing a stream of instructions that includes a set of debug registers for identifying an instruction or data address breakpoint; a processor for generating a debug exception in response to an instruction or data address in the stream of instructions matching the instruction or data breakpoint stored in the set of debug registers and a debug configuration register for enabling transfer of program control to one of a plurality of destinations in response to the debug exception. The debug configuration registers may designate system management mode, JTAG routine or a software debug interrupt handler as the destination.

Debug system allowing programmable selection of alternate debug mechanisms such as debug handler, SMI, or JTAG

A method of data communication between asynchronous processes of a computer system is disclosed in connection with a cache coherency system for a processor-cache used in a multi-master computer system in which bus arbitration signals either are not available to the processor-cache, or are not exclusively relied on by the processor-cache to assure validity of the data in the cache (e.g., a 386-bus compatible computer system using an external secondary cache in which bus arbitration signals are only connected to and used by the secondary cache controller). In an exemplary external-chip implementation, the cache coherency system (120) comprises two PLAs--a FLUSH module (122) and a WAVESHAPING module (124). The FLUSH module (a) receives selected bus cycle definition and control signals from a microprocessor ((110), (b) detects FLUSH (cache invalidation) conditions, i.e., bus master synchronization events, and for each such FLUSH condition, (c) provides a FLUSH output signal. The WAVESHAPING module provides a corresponding CPU/FLUSH signal to the microprocessor with the appropriate set up and hold time. The exemplary bus master synchronization events, or FLUSH conditions, that cause cache invalidation are: (a) hardware generated interrupts, and (b) read or read/write accesses to I/O address space, except for those directed to a hard disk or an external coprocessor. If the bus architecture uses memory-mapped I/O, accesses to selected regions of memory-mapped I/O space could also be used. The cache coherency functionality could be implemented on-board the microprocessor.

Cache coherency without bus master arbitration signals

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Plano, TX, United States of America

William C Patton