National Semiconductor Corporation

Narendra Sankar

Christopher E Phillips

Mario D Nemirovsky

Robert James Divivier

Alexander Perez

Wayne Yamamoto

The present invention is a data word extraction circuit that receives n data words DW.sub.x (for x equal 0 through n-1), where each of the data words DW.sub.x having m bit positions BP.sub.y (for y=0 through m-1). The circuit provides at least one of the data words DW.sub.x to an extraction circuit output responsive to an extraction indicator signal. Specifically, a group of data selector elements DSE.sub.y, each corresponding to a separate one of the bit positions BP.sub.y in the received data words. Each data selector element includes a data output DO.sub.y and a plurality of data inputs DI.sub.x. Each data input DI.sub.x is connected to receive a bit from the bit position BP.sub.y to which the data selector element DSE.sub.y corresponds, of a data word DW.sub.x to which the data input DI.sub.x corresponds. A select input is responsive to the extraction indicator signal such that the data selector element DSE.sub.y provides, at the data output, the bit received at one of the data inputs DI.sub.x that corresponds to the extraction indicator signal. The bits provided at the data outputs of the group of data selector elements are collectively provided to the extraction circuit output.

Area and time efficient extraction circuit

An apparatus and method for efficiently generating the consecutive addresses needed to access misaligned or doubleword length data stored in the memory of a general purpose microprocessor. The apparatus shares the address generation operations between a small 3 bit adder, typically contained in the bus unit, and the execution unit. Control logic is used to determine whether a data misalignment situation exists based on the length of the data which is to be retrieved and the starting address of the data. When misalignment is indicated, the control unit acts to assign the address calculations to either the 3 bit adder alone or the execution unit together with the 3 bit adder depending upon how much the present address must be incremented to obtain the new addresses.

Apparatus and method for efficiently determining addresses for

A method and apparatus for fault testing a pipelined processor. In test mode, the stage registers are reconfigured as multiple input shift registers by switching in a few exclusive-OR gates. Also, the execute stage is prevented from executing any instructions. A unique sequential test sequence of instructions are run through the processor at normal speed. It is known that a particular test sequence (and thus a unique sequential input pattern to the MISR, assuming no faults) will result in a unique signature pattern existing in the MISR at the end of the sequence. If the signature pattern is not found in the MISR at the end of the test sequence, then it is known that a fault exists on the chip.

Method and apparatus for fault testing a pipelined processor

An efficient method for implementing string operations used to process blocks of data within a memory. The registers used to track the memory addresses are updated and committed before the outcome of a read or write address operation is known. In the event an exception occurs, exception handling hardware and microcode is used to restore the state of the registers to the condition they were in prior to the iteration which produced the exception. This reduces the number of microcode instructions required to implement the string operation, producing a faster cycling of the code through multiple iterations. The result is a more optimal code for string operations and a decrease in the time required to carry out the string instruction.

Method of implementing fast 486TM microprocessor compatible string

A partitioned decoder circuit responds to an address signal supplied at a decoder circuit input by providing a result data signal that corresponds to the address signal. Selection signal decoder circuitry asserts one or more of a plurality of decoder enable signals based upon the value of a decoder selection signal. A plurality of decoder circuit elements are each connected to receive a separate one of the asserted decoder enable signals. Each decoder circuit element includes a first clock input coupled to receive a precharge clock signal, an address input coupled to receive the address signal, address latching circuitry that latches the address signal in response to a polarity transition of the precharge clock signal, and a second clock input. Significantly, gated discharge clock signal generation circuitry of each decoder circuit element generates a gated discharge clock signal in response to the asserted decoder enable signal. The gated discharge clock signal is provided to the second clock input. A data output responds to the gated discharge clock signal being provided to the second clock input by providing an evaluation signal that corresponds to the latched address signal such that the result data signal includes the evaluation signal.

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Sunnyvale, CA, United States of America

Narendra Sankar