257 results about "Instruction buffer" patented technology

A processor (100) is provided that is a programmable fixed point digital signal processor (DSP) with variable instruction length, offering both high code density and easy programming. Architecture and instruction set are optimized for low power consumption and high efficiency execution of DSP algorithms, such as for wireless telephones, as well as pure control tasks. The processor includes an instruction buffer unit (106), a program flow control unit (108), an address / data flow unit (110), a data computation unit (112), and multiple interconnecting busses. Dual multiply-accumulate blocks improve processing performance. A memory interface unit (104) provides parallel access to data and instruction memories. The instruction buffer is operable to buffer single and compound instructions pending execution thereof. A decode mechanism is configured to decode instructions from the instruction buffer. The use of compound instructions enables effective use of the bandwidth available within the processor. A soft dual memory instruction can be compiled from separate first and second programmed memory instructions. Instructions can be conditionally executed or repeatedly executed. Bit field processing and various addressing modes, such as circular buffer addressing, further support execution of DSP algorithms. The processor includes a multistage execution pipeline with pipeline protection features. Various functional modules can be separately powered down to conserve power. The processor includes emulation and code debugging facilities with support for cache analysis.

A method of tracking instruction dependency in a processor issuing instructions speculatively includes recording in an instruction dependency array (IDA) an entry for each instruction that indicates data dependencies, if any, upon other active instructions. An output vector read out from the IDA indicates data readiness based upon which instructions have previously been selected for issue. The output vector is used to select and read out issue-ready instructions from an instruction buffer.

The invention discloses a vector crossing multithread processing method and a vector crossing multithread microprocessor. The processing method comprises the following steps: using a multithread instruction-acquiring part to choose a vector thread from N vector threads for reading an instruction and storing the read instruction to a corresponding instruction buffer array of the vector thread; using a thread scheduling part to choose an instruction buffer array from N instruction buffer arrays and taking out an instruction from the instruction buffer array for the purpose of decoding; and sending a decoded instruction to a vector executing streamline or scalar executing streamline so as to execute. The method can be realized by using hardware structure by the vector crossing multithread microprocessor. The method and the microprocessor provided by the invention have the advantages that the vector processing technique and multithread technique are combined, the hardware structure is simple, the operation capability is strong, the compatibility and expansibility are excellent, and the like.

Instruction dispatch in a multithreaded microprocessor such as a graphics processor is not constrained by an order among the threads. Instructions are fetched into an instruction buffer that is configured to store an instruction from each of the threads. A dispatch circuit determines which instructions in the buffer are ready to execute and may issue any ready instruction for execution. An instruction from one thread may be issued prior to an instruction from another thread regardless of which instruction was fetched into the buffer first. Once an instruction from a particular thread has issued, the fetch circuit fills the available buffer location with the following instruction from that thread.

This is an instruction fetch control device supplying instructions to an instruction execution unit. The device comprises a plurality of instruction buffers storing an instruction string to be supplied to the instruction execution unit and a designation unit designating an instruction buffer storing the instruction string to be supplied next for each of the plurality of instruction buffers.

A method and apparatus for dynamically managing instruction buffer depths for non-predicted branches reduces wasted energy and resources associated with low confidence branch prediction conditions. A portion of the instruction buffer for a instruction thread is allocated for storing predicted branch instruction streams and another portion, which may be zero-sized during high prediction confidence conditions, is allocated to the non-predicted branch instruction stream. The size of the buffers is adjusted dynamically in conformity with an on-going prediction confidence that provides a measure of how well branch prediction mechanisms are working for a given instruction thread. An alternate instruction fetch address table can be maintained and multiplexed with the main fetch address register for addressing the instruction cache, so that the instruction stream can be quickly shifted to the non-predicted path when a branch instruction is resolved to the non-predicted path.

A system and method for optimizing the branch logic of a processor to improve handling of hard to predict indirect branches are provided. The system and method leverage the observation that there will generally be only one move to the count register (mtctr) instruction that will be executed while a branch on count register (bcctr) instruction has been fetched and not executed. With the mechanisms of the illustrative embodiments, fetch logic detects that it has encountered a bcctr instruction that is hard to predict and, in response to this detection, blocks the target fetch from entering the instruction buffer of the processor. At this point, the fetch logic has fetched all the instructions up to and including the bcctr instruction but no target instructions. When the next mtctr instruction is executed, the branch logic of the processor grabs the data and starts fetching using that target address. Since there are no other target instructions that were fetched, no flush is needed if that target address is the correct address, i.e. the branch prediction is correct.

A branch control apparatus in a microprocessor. A register receives a first cache line containing a branch instruction from an instruction cache in response to a fetch address. The fetch address hits in a BTAC that provides a target address of the branch instruction. The BTAC also provides an offset of the instruction following the branch instruction. The instructions following the branch instruction are invalidated based on the offset. Muxing logic packs only the valid instructions into a byte-wide instruction buffer that is directly coupled to instruction format logic. The instruction cache provides a second cache line containing the target instructions to the register in response to the target address. The instructions preceding the target instructions are invalidated based on the lower bits of the target address. The muxing logic packs only the valid target instructions into the instruction buffer immediately adjacent to the branch instruction bytes.

A circuit arrangement and method selectively bypass an instruction buffer for selected instructions so that bypassed instructions can be dispatched without having to first pass through the instruction buffer. Thus, for example, in the case that an instruction buffer is partially or completely flushed as a result of an instruction redirect (e.g., due to a branch mispredict), instructions can be forwarded to subsequent stages in an instruction unit and / or to one or more execution units without the latency associated with passing through the instruction buffer.

A fetch director in a multithreaded microprocessor that concurrently executes instructions of N threads is disclosed. The N threads request to fetch instructions from an instruction cache. In a given selection cycle, some of the threads may not be requesting to fetch instructions. The fetch director includes a circuit for selecting one of threads in a round-robin fashion to provide its fetch address to the instruction cache. The circuit adds a first addend to a 1-bit left-rotated version of a second addend to generate a sum and a carry-out bit. The circuit includes the carry-out bit as a carry-in bit of the add to generate the sum. The sum is ANDed with the inverse of the first addend to generate a 1-hot vector indicating which of the threads is selected next. The first addend is an N-bit vector where each bit is false if the corresponding thread is requesting to fetch instructions from the instruction cache. The second addend is a 1-hot vector indicating the last selected thread. In one embodiment threads with an empty instruction buffer are selected at highest priority; a last dispatched but not fetched thread at middle priority; all other threads at lowest priority. The threads are selected round-robin within the highest and lowest priorities.

A fetch director in a multithreaded microprocessor that concurrently executes instructions of N threads is disclosed. The N threads request to fetch instructions from an instruction cache. In a given selection cycle, some of the threads may not be requesting to fetch instructions. The fetch director includes a circuit for selecting one of threads in a round-robin fashion to provide its fetch address to the instruction cache. The circuit 1-bit left rotatively increments a first addend by a second addend to generate a sum that is ANDed with the inverse of the first addend to generate a 1-hot vector indicating which of the threads is selected next. The first addend is an N-bit vector where each bit is false if the corresponding thread is requesting to fetch instructions from the instruction cache. The second addend is a 1-hot vector indicating the last selected thread. In one embodiment threads with an empty instruction buffer are selected at highest priority; a last dispatched but not fetched thread at middle priority; all other threads at lowest priority. The threads are selected round-robin within the highest and lowest priorities.