Tandem Computers Incorporated

Leonard E Overhouse

Daniel E Lenoski

Richard F Boyle

A synchronous processor unit is divided into two sections, and each separately clocked by different clock signals. One section, containing an instruction execution unit and memory for storage of instructions and data, is clocked at a higher frequency, while the other section, containing those elements of a processor unit less frequently used, are clocked with a slower-frequencied clock. The elements of each section are intercoupled by separate and independent data buses, and selectively to one another by a buffer unit. The clock signals used by both sections are produced by a clock-generating unit which also monitors the instructions being executed by the instruction execution unit. When an instruction requiring communication between the two sections is detected, at least one predetermined transition of each of the fast and slow clocks are synchronized, and during this synchronization the separate buses of each section are coupled to one another by the buffer unit for information exchanges therebetween.

Synchronous processor unit with interconnected, separately clocked

Apparatus is disclosed for generating pseudo-random bit patterns that are applied to a data processor, or other digital logic unit, for test purposes. In accordance with the invention, certain of the elemental storage units (e.g., flipflops) of the data processor are designed for two-mode operation: A normal mode of operation during which they operate as a part of the data processor in normal fashion, and a scan mode operation during which the elemental storage units respond to scan control signals to form a number of shift register or scan line configurations for receiving the pseudo-random sequenced or non-random sequenced test patterns generated by the apparatus. During testing, the bit patterns are passed through the scan line configurations and applied to compression circuits where, using cyclic redundancy checking (CRC), compression bit patterns received from the scan lines are achieved. Produced are test signatures that are stored in a memory for later comparison with standardized signatures to determine the PASS/FAIL condition of the processor. Tests can be preceded and followed by a controlled scan of the digital logic to save and restore the operational state of the digital logic. In this manner, test interruptions are relatively unobtrusive and essentially transparent to the logic tested.

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Los Gatos, CA, United States of America

Leonard E Overhouse