Abstract: Methods and systems are provided for debugging a program executing on a processor. In a first implementation, a processing system includes a processor configured for switching to a debug mode from a non-debug mode upon executing a software breakpoint. The system may include a program memory configured to hold instructions for a program, where the software breakpoint replaces at least one of the instructions. The system may also include an instruction replacement register separate from the program memory that is configured to receive the replaced instruction from any of the processor and an external debugger. The system may further include a control component that controls whether the processor fetches a next instruction for execution from the program memory or from the instruction replacement register.

Abstract: A packed half-word addition and subtraction operation is performed by a microprocessor in parallel upon half-word operands obtained from designated top or bottom half-word locations of designated source registers of a register file and the sum and difference results of such operation are packed into respective top and bottom half-word locations of a designated destination register. The microprocessor includes an arithmetic-logic unit (ALU) with adder circuitry that can be selectively split into separate half-word adders that are independently selectable to perform either an addition operation or subtraction operation upon the selected half-word operands. The half-word adders of the ALU access the operands from source registers via a set of multiplexers that select among the top and bottom half-word locations. Operations with halving and saturation modifications to the sum and difference results may also be provided.

Abstract: An apparatus comprises register means for storing a return context upon initiation of a supervisor call instruction and restoring means to restore a privilege level and status register upon execution of a supervisor return instruction. The supervisor call instruction can be called from all contexts.

Abstract: An adaptation of the sum-of-absolute-differences (SAD) calculation is implemented by modifying existing circuitry in a microprocessor. The adaptation yields a reduction of over 30% for a current SAD calculation. The adaptation includes a first and second operand register, each storing respectively a first and second set of 2's complement binary data, an arithmetic logic unit (ALU), and a destination register. An add/subtract enable input on the ALU receives a most significant bit (MSB) of the second set of binary data. The ALU adds the first and second data sets if the MSB is a “0” and subtracts the second data set from the first data set if the MSB is a “1.” The add/subtract enable input has the effect of taking the absolute value of the second data set without having to first perform an absolute value determination, thus eliminating processing steps.

Abstract: A method and medium for performing subroutine return operations. Test operations are performed in parallel with other operations in a return operation. These test operations and the return operations are performed in response to a single instruction.

Abstract: An apparatus for scaling numbers comprises register means for storing an operand to be scaled, bit shifting means for performing a right shift operation on the operand, rounding means, and decision means to test for the existence of at least one of an overflow and an underflow condition.

Abstract: An apparatus and method for saving and operating on a register set, shadow register file, and memory is presented. A register within a register set that is associated with an active execution state in a computing system is used as an address pointer to a memory location. The content of the memory location is either loaded from memory into an identified shadow register, or the content of a shadow register is stored into the memory location. The operation is normally performed by executing a single instruction by a processor or by circuitry associated with a processor or computer system. Active and inactive execution states may be under the control of an operating system running on the processor or computer system.

Abstract: A system and method for preserving power in a microprocessor pipeline. The system includes a register file read control unit, the read control unit being configured to monitor one or more outputs from a control/decode unit of the pipeline and monitor write addresses from one or more other stages of the pipeline. The system also includes one or more read inhibit units each having an input, an output, and an enable terminal, the output of each of the one or more read inhibit units being coupled to a unique register port of a register file within the pipeline. The input of each of the one or more read inhibit units being coupled to the control/decode unit, and the enable terminal of each of the one or more read inhibit units being coupled to a unique output of the read control unit.

Abstract: An apparatus for performing multiply-accumulate operations in a microprocessor comprising operand input registers for receiving data to be operated on an adder and a multiplier for performing operations on the data, a result output port for presenting results to the microprocessor, a multiplexer for storing results, an accumulator cache for storing an accumulator value internal to the apparatus, and control circuitry for controlling the operation of the apparatus.

Abstract: A microprocessor circuit useful for indexed addressing of byte-addressable memories includes word-length index, base address, and destination registers designated by an instruction. The instruction also specifies one byte packed within the index register, which is to be extracted. A multiplexer has a word-wide input end accessing all of the bytes of the index register, and responsive to byte selection control passes the specified byte to its output. The extracted byte is provided directly at specific bit positions of a zero-extended address offset word. The offset word is added to the base address, the sum being used to address memory contents that are loaded into the destination register.

Abstract: A combined native (RISC or CISC) microprocessor and stack (Java) machine are constructed so that Java VM instructions can be executed in hardware. Most Java instructions are executed directly, while more complex Java instructions, such as those manipulating Java objects, are executed as native microcode. In order for native microcode instructions to access the Java operand stack, a Java operand stack pointer points to the register file location that is the current top of the stack, while a remap bit in the status register indicates that registers specified in native instructions are remapped as the maximum Java operand stack pointer value minus the present value of the Java operand stack pointer.