Abstract: A processor includes a conditional branch instruction prediction mechanism that generates weighted branch prediction values. For weakly weighted predictions, which tend to be less accurate than strongly weighted predictions, the power associating with speculatively filling and subsequently flushing the cache is saved by halting instruction prefetching. Instruction fetching continues when the branch condition is evaluated in the pipeline and the actual next address is known. Alternatively, prefetching may continue out of a cache. To avoid displacing good cache data with instructions prefetched based on a mispredicted branch, prefetching may be halted in response to a weakly weighted prediction in the event of a cache miss.

Abstract: One or more architected registers in a processor are fractional-word writable, and data from plural misaligned memory access operations are assembled directly in an architected register, without first assembling the data in a fractional-word writable, non-architected register and then transferring it to the architected register. In embodiments where a general-purpose register file utilizes register renaming or a reorder buffer, data from plural misaligned memory access operations are assembled directly in a fractional-word writable architected register, without the need to fully exception check both misaligned memory access operations before performing the first memory access operation.

Abstract: Techniques for controllably allocating a portion of a plurality of memory banks as cache memory are disclosed. To this end, a configuration tracker and a bank selector are employed. The configuration tracker configures whether each memory bank is to operate in a cache or not. The bank selector has a plurality of bank distributing functions. Upon receiving an incoming address, the bank selector determines the configuration of memory banks currently operating as the cache and applies an appropriate bank distributing function based on the configuration of memory banks. The applied bank distributing function utilizes bits in the incoming address to access one of the banks configured as being in the cache.

Abstract: Method and apparatus for reformatting instructions in a pipelined processor. An instruction register holds a plurality of instructions received from a cache memory external to the processor. A predecoder predecodes each of the instructions and determines from an instruction operation field where the instruction fields should be placed. A multiplexer reformats architecturally aligned instructions into hardware implementation aligned instructions prior to storing into L1 cache, so that the instructions are ready for dispatch to the pipeline execution units.

Abstract: In a pipelined processor, a pre-decoder in advance of an instruction cache calculates the branch target address (BTA) of PC-relative and absolute address branch instructions. The pre-decoder compares the BTA with the branch instruction address (BIA) to determine whether the target and instruction are in the same memory page. A branch target same page (BTSP) bit indicating this is written to the cache and associated with the instruction. When the branch is executed and evaluated as taken, a TLB access to check permission attributes for the BTA is suppressed if the BTA is in the same page as the BIA, as indicated by the BTSP bit. This reduces power consumption as the TLB access is suppressed and the BTA/BIA comparison is only performed once, when the branch instruction is first fetched. Additionally, the pre-decoder removes the BTA/BIA comparison from the BTA generation and selection critical path.

Abstract: In a pipelined processor where instructions are pre-decoded prior to being stored in a cache, an incorrectly pre-decoded instruction is detected during execution in the pipeline. The corresponding instruction is invalidated in the cache, and the instruction is forced to evaluate as a branch instruction. In particular, the branch instruction is evaluated as “mispredicted not taken” with a branch target address of the incorrectly pre-decoded instruction's address. This, with the invalidated cache line, causes the incorrectly pre-decoded instruction to be re-fetched from memory with a precise address. The re-fetched instruction is then correctly pre-decoded, written to the cache, and executed.

Abstract: A processing system and method of communicating within the processing system is disclosed. The processing system may include a bus; a memory region coupled to the bus; and a plurality of processing components having access to the memory region over the bus, each of the processing components being configured to perform a semaphore operation to gain access to the memory region by simultaneously requesting a read operation and a write operation to a semaphore location over the bus.

Abstract: A method and system for monitoring the real-time of software running on a microprocessor system. Debug hardware is used to select a range of instructions or events to be monitored by a performance monitor interval with the microprocessor system. A comparison is made between each event and start and stop events are identified in the debug hardware. The performance monitor is enabled by the debug hardware, when events occur within the range defined by the debug hardware. Use of the debug hardware for enabling performance monitoring avoids any overhead associated with generating interrupts, or additional code in the application program.

Abstract: An LRU array and method for tracking the accessing of lines of an associative cache. The most recently accessed lines of the cache are identified in the table, and cache lines can be blocked from being replaced. The LRU array contains a data array having a row of data representing each line of the associative cache, having a common address portion. A first set of data for the cache line identifies the relative age of the cache line for each way with respect to every other way. A second set of data identifies whether a line of one of the ways is not to be replaced. For cache line replacement, the cache controller will select the least recently accessed line using contents of the LRU array, considering the value of the first set of data, as well as the value of the second set of data indicating whether or not a way is locked. Updates to the LRU occur after each pre-fetch or fetch of a line or when it replaces another line in the cache memory.

Abstract: A method and system for avoiding various hazards for instructions which are propagating through a microprocessor pipeline. When a plurality of instructions exist within the pipeline which read and write the same value, a vector is established to distinguish the older from the newer instructions. Further, before instructions are dispatched for execution, pointers are generated which identify the particular instruction which had the operand or parameter value needed. Accordingly, by monitoring both the recent vector and pointers, dated dependency hazards can be avoided.

Abstract: A method, computer system and set of signals are disclosed allowing for communication of a data transfer, via a bus, between a master and a slave using a single transfer request regardless of transfer size and alignment. The invention provides three transfer qualifier signals including: a first signal including a starting byte address of the data transfer; a second signal including a size of the data transfer in data beats; and a third signal including a byte enable for each byte required during a last data beat of the data transfer. The invention is usable with single or multiple beat, aligned or unaligned data transfers. Usage of the three transfer qualifier signals provides the slave with how many data beats it will transfer at the start of the transfer, and the alignment of both the starting and ending data beats. As a result, the slave need not calculate the number of bytes it will transfer.

Abstract: A method and apparatus for executing instructions in a pipeline processor. The method decreases the latency between an instruction cache and a pipeline processor when bubbles occur in the processing stream due to an execution of a branch correction, or when an interrupt changes the sequence of an instruction stream. The latency is reduced when a decode stage for detecting branch prediction and a related instruction queue location have invalid data representing a bubble in the processing stream. Instructions for execution are inserted in parallel into the decode stage and instruction queue, thereby reducing by one cycle time the length of the pipeline stage.

Abstract: A system and method for accessing a data cache having at least two ways for storing data at the same addresses. A first and second tag memory store first and second sets of tags identifying data stored in each of the ways. A translation device determines from a system address a tag identifying one of the ways. A first comparator compares tags in the address with a tag stored in the first tag memory. A second comparator compares a tag in the address with a tag stored in the second tag memory. A clock signal supplies clock signals to one or both of the ways in response to an access mode signal. The system can be operated so that either both ways of the associative data cache are clocked, in a high speed access mode, or it can apply clock signals to only one of the ways selected by an output from the first and second comparators in a power efficient mode of operation.

Abstract: A random access memory circuit comprises a plurality of memory cells and at least one decoder coupled to the memory cells, the decoder being configurable for receiving an input address and for accessing one or more of the memory cells in response thereto. The random access memory circuit further comprises a plurality of sense amplifiers operatively coupled to the memory cells, the sense amplifiers being configurable for determining a logical state of one or more of the memory cells. A controller coupled to at least a portion of the sense amplifiers is configurable for selectively operating in at least one of a first mode and a second mode. In the first mode of operation, the controller enables one of the sense amplifiers corresponding to the input address and disables the sense amplifiers not corresponding to the input address. In the second mode of operation, the controller enables substantially all of the sense amplifiers.

Abstract: A method of designing a system on a chip (SoC) to operate with varying latencies and frequencies. A layout of the chip is designed with specific placement of devices, including a bus controller, initiator, and target devices. The time for a signal to propagate from a source device to a destination device is determined relative to a default propagation time. A pipeline stage is then inserted into a bus path between said source device and destination device for each additional time the signal takes to propagate. Each device (i.e., initiators, targets, and bus controller) is designed with logic to control a protocol that functions with a variety of response latencies. With the additional logic, the devices do not need to be changed when pipeline stages are inserted in the various paths. Registers are utilized as the pipeline stages that are inserted within the paths.