Abstract: A processor (100) includes an issue unit (125) having an issue queue (144) for issuing instructions to an execution unit (140). The execution unit (140) may accept and execute the instruction or produce a reject signal. After each instruction is issued, the issue queue (144) retains the issued instruction for a critical period. After the critical period, the issue queue (144) may drop the issued instruction unless the execution unit (140) has generated a reject signal. If the execution unit (140) has generated a reject signal, the instruction is eventually marked in the issue queue (144) as being available to be reissued. The length of time that the rejected instruction is held from reissue may be modified depending upon the nature of the rejection by the execution unit (140). Also, the execution unit (140) may conduct corrective actions in response to certain reject conditions so that the instruction may be fully executed upon reissue.

Abstract: An improved load data formatter and methods for improving load data formatting and for cache line data organization are disclosed. The load data formatter includes a data selection mechanism, the data selection mechanism receiving a data cache line of a predetermined organization, and the data selection mechanism further supporting adjacent word swapping in the cache line. The load data formatter further includes at least two word selectors coupled to an output of the data selection mechanism, the at least two word selectors forming a doubleword on a chosen word boundary of the cache line. In a further aspect, the predetermined organization of the cache line is provided by grouping each corresponding bit of each byte in a cache line of data together, and expanding the grouping with an organization formed by one bit from a same byte within each word.

Abstract: A method and system in a data processing system for accessing information using an instruction specifying a memory address is disclosed. The method and system comprises issuing the instruction to an execution unit and storing an address derived from the specified address. The method and system also includes accessing a cache to obtain the information, using the derived address and determining, in response to a signal indicating that there has been a cache miss, if there is a location available to store the specified address in a queue. According to the system and method disclosed herein, the present invention allows for dynamic pipeline expansion of a processor without splitting this function between components depending upon the reason expansion was required, thereby increasing overall system performance.

Abstract: In a superscalar processor implementing out-of-order dispatching and execution of load and store instructions, when a store instruction has already been translated, the load address range of a load instruction is contained within the address range of the store instruction, and the data associated with the store instruction is available, then the data associated with the store instruction is forwarded to the load instruction so that the load instruction may continue execution without having to be stalled or flushed.

Abstract: An apparatus and method for processing multiple cache misses to a single cache line in an information handling system which includes a miss queue for storing requests for data not located in a level one cache and a comparator for comparing requests for data stored in the miss queue to determine if there are multiple requests for data located in the same cache line of a level two cache. Each new request for data from the same cache line of the level two cache as an older original request for data in the miss queue is marked as a load hit reload. The requests marked as load hit reloads are then grouped together with the matching original request and forwarded together to the level two cache wherein the original request requests the data from level two cache. The load hit reload requests do not access level two cache but instead bypass access of level two cache by extracting data from the cache line outputted from level two cache for the matching original request.

Abstract: A data processing system has a memory bus and a system input/output (I/O) bus including I/O drivers. The memory and I/O buses are controlled by a central processor unit (CPU) for transferring data therebetween and to the I/O drivers. A central clock provides clock signals to the CPU, the memory bus and the I/O bus. The central clock further provides memory and I/O phase alignment signals to the CPU, the alignment signals indicating to the CPU when the start of the CPU clock cycle coincides with the start of a memory bus clock cycle or I/O bus clock signal. Circuit means responsive to the phase alignment and CPU clock signals initiate the transfer of data to the memory and I/O data buses in alternate CPU clock signals to reduce the number of I/O pin switching at any given time thereby reducing the noise and power consumption at the I/O pins and in the system.

Abstract: To support load instructions which execute out-of-order with respect to store instructions, a mechanism is implemented to detect (and correct) the occurrences where a load instruction executed prior to a logically prior store instruction, and where the load instruction received data for the location prior to being modified by the store instruction, and the correct data for the load instruction included bytes from the store instruction. Additionally, to execute store instructions out-of-order with respect to load instructions, a mechanism is implemented to keep a store instruction from destroying data that will be used by a logically earlier load instruction. Further, to support load instructions that are executed out-of-order with respect to each other, a mechanism is implemented to insure that any pair of load instructions (which access at least one byte in common) return data consistent with executing the load instructions in order.