Cyrix Corporation

National Semiconductor Corporation

Via-cyrix, Inc.

Mark W Hervin

Raul A Garibay, Jr

Mark W Bluhm

Steven C McMahan

Marc A Quattromani

Nital Patwa

Ronald S McMahon

William C Patton

David B Erickson

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 microprocessor comprises a plurality of instruction pipelines having a plurality of stages for processing a stream of instructions, circuitry for simultaneously issuing instructions into two or more of the pipelines without regard to whether one of the simultaneously issued instructions has a data dependency on other of the simultaneously issued instructions, detecting circuitry for detecting dependencies between instructions in the pipelines and circuitry for controlling the flow of instructions through the pipelines such that an instruction is not delayed due to a data dependency on another instruction unless the data dependency must be resolved for proper processing of the instruction in its current stage.

Processor with multiple execution pipelines using pipe stage state

A microprocessor comprises one or more instruction pipelines having a plurality of stages for processing a stream of instructions, with one or more of said instructions referencing a set of logical registers. A plurality of physical registers are allocated to store data associated with the logical registers by register translation circuitry. The register translation circuitry is selectively controlled by the microcode or by hardware signals generated by one or more of the stages.

Pipelined processor with microcontrol of register translation hardware

Circuit for performing arithmetic operations in a 32-bit architecture. The circuit includes a five stage shift and rotate circuit coupled between first and second 32-bit busses in the following sequence: an 8-bit shift and rotate circuit, a 16-bit shift and rotate circuit, a 1-bit shift and rotate circuit, a 2-bit shift and rotate circuit and a 4-bit shift and rotate circuit. For double word sized (32-bit) operands, the variously sized shift and rotate circuits may be selectively enabled to perform between 1-bit and 31-bit shift/rotate/pass operations. For byte sized operands, the 8-bit and 16-bit shift and rotate circuits are used to pre-process the operands while the 1-bit, 2-bit and 4-bit shift and rotate circuits are selectively enabled to perform the full range, i.e., 1-bit to 7-bit, of possible shift/rotate operations. For word sized (16-bit) operands, the 16-bit or 8-bit and 16-bit shift and rotate circuits are used to pre-process the operands while the 1-bit, 2-bit and 4-bit shift and rotate circuits are selectively enabled to perform the full range of shift/rotate operations.

Microprocessor having combined shift and rotate circuit

A processor for outputting processor state information during idle bus cycles to facilitate the diagnosing and debugging of a processor. The processor includes a plurality of external pins for communicating data from the processor; a visibility register for selecting one of a plurality of modes which identifies processor state information to output onto the plurality of external pins; and a bus interface unit for communicating data to the external pins of the processor and for detecting an idle bus cycle. The bus interface unit outputs processor state information according to the identified mode onto the plurality of external pins in response to detecting an idle bus cycle.

Debugging a processor using data output during idle bus cycles

A system and method of readily identifying and handling self-modifying variable length instructions in a pipelined processor is disclosed employing index tags associated with each stage of the execution pipeline wherein the index tags identify the cache line numbers in the instruction cache from which the instructions originate.

Method of identifying and self-modifying code

In a pipelined processor having at least one execution pipeline for executing instructions, the execution pipeline including ID (decode), AC (address calculation), and EX (execution) processing stages, the processor capable of addressing segments of system memory coupled thereto, a circuit for, and method of, setting a segment access indicator associated with a segment of the system memory being accessed by the processor. The circuit includes: (a) exception generating circuitry to generate an exception when the segment access indicator requires setting and (b) exception handling circuitry, invoked by the processor in response to generation of the exception, to flush the execution pipeline of instructions following a segment load instruction, set the segment access indicator and load an address pointer of the processor with an address corresponding to a specified location within the segment.

In a pipelined processor, setting a segment access indicator during

A processor architecture and methodology for executing a condition dependent instruction over a plurality of execution stages in a microprocessor. The microprocessor includes a memory for storing microinstructions. The method involves various steps. In one step, an instruction is received. In another step, a first microinstruction is issued from the memory. This first microinstruction comprises a control and a base address. In yet another step, a secondary address is determined, external from the memory, by evaluating a plurality of predetermined data. In a still another step, the base address and the secondary address are combined to form a destination address in response to the control signal, wherein the destination address identifies a second microinstruction in the memory to execute a successive stage for the received instruction.

Microprocessor having expedited execution of condition dependent

In an .chi.86-compatible processor capable of operating in a protected mode of operation in which privilege levels are assigned to tasks executing therein, an application task being assigned a lowest privilege level and executable in the processor to cause the processor to calculate addresses corresponding to specific locations in a computer memory associated with the processor, the addresses to be in alignment with respect to the computer memory prior to the processor issuing the addresses, a circuit for, and method of, handling sequential alignment faults and a computer system embodying the same. The circuit includes: (1) an alignment detection circuit to detect an alignment fault and generate an alignment check exception in response thereto and (2) an alignment fault-handling routine associated with the processor, executable in response to generation of the alignment check exception, operable to detect a sequential alignment fault and generate a double fault exception in response thereto, the alignment fault-handling routine thereby allowing the processor to avoid a third sequential alignment fault.

Error-handling circuit and method for memory address alignment double

A processor includes storage circuitry for storing an instruction and memory circuitry addressable by a microaddress for outputting a microinstruction in response to the microaddress. The processor further includes sequencing circuitry coupled to provide the microaddress to the memory circuitry. Finally, the processor includes decode circuitry coupled to the storage circuitry for detecting whether the instruction stored in the storage circuitry comprises a single clock instruction before the memory circuit outputs the microinstruction, and for indicating to the sequencing circuitry in response to detecting whether the instruction stored in the storage circuitry comprises a single clock instruction.

Processor with single clock decode architecture employing single microROM

In a processor having a protected mode of operation in which a computer memory associated with the processor contains global and local descriptor tables addressed by a combination of a base address and an index, the processor having (i) global and local base address registers alternatively to provide the base address and (ii) a selector for containing the index and a table indicator (TI) bit indicating which of the global and local base address registers is to provide the base address, the processor requiring a time to derive the index and a value of the TI bit and a further time to combine the index and the base address, a base address register predicting circuit to predict, and a method of predicting, which of the global and local base address registers is to provide the base address without having to wait for the processor to derive the value of the TI bit. The circuit includes (i) TI bit predicting circuitry to generate a predicted value of the TI bit as a function of a prior value of the TI bit, and (ii) register access circuitry to access one of the global and local base address registers as a function of the predicted value of the TI bit.

Circuit and method for addressing segment descriptor tables

A sequencer for use in a pipeline architecture includes circuitry for determining whether the previous instruction was a conditional jump instruction and whether the condition was met, circuitry for determining whether the current instruction is a conditional jump, and circuitry inhibiting a branch responsive to the current instruction, if the previous instruction was a conditional jump and the condition was met. Additionally, circuitry may be provided for treating a CALL instruction as a one-cycle unconditional jump if the preceding instruction was a conditional jump and the condition was not met, thereby implementing a two-cycle IF-THEN-ELSE instruction.

Microsequencer allowing a sequence of conditional jumps without

A superscalar superpipelined microprocessor having a write buffer located between the core and cache is disclosed. The write buffer is controlled to store the results of write operations to memory until such time as the cache becomes available, such as when no high-priority reads are to performed. The write buffer includes multiple entries that are split into two circular buffer sections for facilitating the interaction with the two pipelines of the core; cross-dependency tables are provided for each write buffer entry to ensure that the data is written from the write buffer to memory in program order, considering the possibility of prior data present in the opposite section. Non-cacheable reads from memory are also ordered in program order with the writing of data from the write buffer. Features for handling speculative execution, detecting and handling data dependencies and exceptions, and performing special write functions (misaligned writes and gathered writes) are also disclosed.

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Dallas, TX, United States of America

Mark W Hervin