摘要:
In a microcomputer system implementing a cache memory subsystem, the cache performance on write allocation cycles is improved. When the processor writes to a line of the cache memory that results in a cache tag miss, after the processor write operation is suspended, the data is allocated from main memory into the cache memory. During this main memory read, however, instead of setting the state of the line of memory to unmodified, its state is set to modified. On the subsequent processor read operation, a cycle is saved because the modified bit does not have to be changed from unmodified to modified.
摘要:
A method for arbitrating between processor and host bus snoop accesses to a cache subsystem in a multiprocessor system where the processor does not allow for processor cycle aborts. When a processor access and a snoop access both occur and no tag access or tag modify cycle is currently being performed, the snoop access is given priority over the processor access. After an initial arbitration, if any, the processor and snoop accesses alternate tag access if both processor and snoop accesses are active. This balances any wait states incurred between the processor and the host bus and ensures that neither bus is locked out by continual accesses by the other. In addition, tag modify cycles are generally run immediately after the tag access cycles that initiate them.
摘要:
Method and apparatus for improving processor performance. In some embodiments, processing speed may be improved by reusing data stored in a buffer during an initial request by subsequent requests. Assignment of temporary storage buffers in a controller may be made to allow for the potential for reuse of the data. Further, a hot buffer may be designated to allow for reuse of the data stored in the hot buffer. On subsequent requests, data stored in the hot buffer may be sent to a requesting device without re-retrieving the data from memory.
摘要:
A memory controller which provides a series of queues between the processor and the PCI bus and the memory system. Memory coherency is maintained in two different ways. Before any read operations are accepted from the PCI bus, both of the posting queues must be empty. A content addressable memory (CAM) is utilized as the PCI to memory queue. When the processor performs a read request, the CAM is checked to determine if one of the pending write operations in the PCI to memory queue is to the same address as the read operation of the processor. If so, the read operation is not executed until the PCI memory queue is cleared of the write. To resolve the problem of aborting a Memory Read Multiple operation, an abort signal from the PCI bus interface is received and as soon thereafter as can be done the read ahead cycle is terminated, even though the read ahead cycle has not fully completed. The memory controller has improved prediction rules based on whether the cycle is coming from the processor or is coming from the PCI bus to allow more efficient precharging when PCI bus cycles are used. The memory controller is highly programmable for multiple speeds and types of processors and several speeds of memory devices.
摘要:
Access to a bus in a computer system having a CPU and bus devices capable of running cycles on a bus is controlled by an arbiter. The arbiter grants access to the bus according to an arbitration scheme that depends on whether a request for the bus is pending from the CPU, in which a first arbitration scheme arbitrates between the bus devices, and wherein a second arbitration scheme arbitrates between the CPU and at least one other bus device if the CPU request is present.
摘要:
In a microcomputer system implementing cache memory, a multiple-way cache is implemented in a single-bank memory. Instead of using chip output enables on a separate physical chip for each way of the multiple-way cache, an address line of a single bank of memory is used to select between ways. In this way, fewer parts can be used, and a single-bank memory can be used for a multiple-way cache.
摘要:
A circuit for placing an external or L2 cache memory into low power mode in response to certain special cycles executed by the microprocessor. In particular, the special cycles are the stop grant acknowledge special cycle and the halt special cycle. The microprocessor executes the stop grant acknowledge special cycle in response to a request by the computer system to slow down its clock. This request is asserted by the computer system if the system has been idle for a predetermined period of time. The halt special cycle is generated by the microprocessor when a HALT instruction is executed. The stop grant acknowledge and halt special cycles place the microprocessor into a low power state. Since the microprocessor is in low power mode, the L2 cache memory is also placed into low power mode for further power conservation. The L2 cache memory is implemented either with synchronous or asynchronous static random access memories (SRAMs). To place a synchronous SRAM into low power mode, its address strobe input is asserted while its chip select input is deasserted. For an asynchronous SRAM, deasserting its chip select input causes the SRAM to transition into low power mode.
摘要:
In a microcomputer system using a multiple-way cache memory subsystem, the way of the next microprocessor operation is predicted, and either the output enables of the cache are predriven, or, in a single-bank multiple-way cache, the address bit which acts as a way selection is appropriately set. The way prediction used is based not on the address being accessed in the cache, but instead on the last processor code read, or the last processor code or data read. This permits the cache memory subsystem to respond more quickly on hits to the appropriate way, and also allows for slower cache memories to be used without reducing performance.
摘要:
A circuit for placing an external or L2 cache memory into low power mode in response to certain special cycles executed by the microprocessor. In particular, the special cycles are the stop grant acknowledge special cycle and the halt special cycle. The microprocessor executes the stop grant acknowledge special cycle in response to a request by the computer system to slow down its clock. This request is asserted by the computer system if the system has been idle for a predetermined period of time. The halt special cycle is generated by the microprocessor when a HALT instruction is executed. The stop grant acknowledge and halt special cycles place the microprocessor into a low power state. Since the microprocessor is in low power mode, the L2 cache memory is also placed into low power mode for further power conservation. The L2 cache memory is implemented either with synchronous or asynchronous static random access memories (SRAMs). To place a synchronous SRAM into low power mode, its address strobe input is asserted while its chip select input is deasserted. For an asynchronous SRAM, deasserting its chip select input causes the SRAM to transition into low power mode.
摘要:
In a microcomputer system implementing a cache memory subsystem, the cache performance on write allocation cycles is improved. When the processor writes to a line of the cache memory that results in a cache tag miss, after the processor write operation is suspended, the data is allocated from main memory into the cache memory. During this main memory read, however, instead of setting the state of the line of memory to unmodified, its state is set to modified. On the subsequent processor read operation, a cycle is saved because the modified bit does not have to be changed from unmodified to modified.