Abstract: A combination asynchronous cache system and automatic clock tuning device is disclosed in which the automatic clock tuning device includes at least a pulse generator, a counter, a unit delay tree, a comparing device, and a feedback path. A portion of the feedback path delivers a signal of interest off of the device chip in order that the signal experience the effect of the actual system impedance prior to being returned to the device chip for further manipulation of the signal. A major concept of the automatic clock tuning device is to enable a cache data/tag Write Enable (WE) signal to be clocked off of the falling edge of a delayed version of the System Clock (SCLK). This Delayed Clock (DCLK) signal is automatically delayed by a pre-selected amount each time that the rising edge of the WE signal occurs earlier than the rising edge of the SCLK signal.

Abstract: A Tag Field for a second level cache memory subsystem in a PC is provided which replaces the fixed Valid and Dirty bits with programmable bits which can each be programmed as a Valid bit, a Dirty bit, or an additional address bit. The cacheable address space of the PC can thus be increased by programming one or more of the two programmable bits as additional address bits. This method can be implemented on existing computers by modifying the system or application software to utilize these programmable bits in a manner to achieve more optimum performance of the cache.

Abstract: A low-cost, moderate performance small computer system is provided by allowing a single sharable block of memory to be independently accessible as graphics or main store memory. Allocation of the memory selected programmably, eliminating the need to have the maximum memory size for each block simultaneously. Performance penalties are minimized by dynamically allocating the memory bandwidth on demand rather than through fixed time slices. Efficient L2 cache memory support is provided based on a system controller having an integrated L2 cache controller and a graphics controller that supports an integrated memory system. The memory connected to the graphics controller may be partitioned into two sections, one for graphics and one for system use. Additionally, the system controller may or may not have attached additional memory for system use. L2 cache support is provided for all system memory, regardless of the controller that it is connected to.

Abstract: A multiprocessing system includes a cache coherency technique that ensures that every access to a line of data is the most up-to-date copy of that line without storing cache coherency status bits in a global memory and any reference thereto. An operand cache includes a first directory which directly, on a one-to-one basis, maps a range of physical address bits into a first section of the operand cache storage. An associative directory multiply maps physical addresses outside of the range into a second section of the operand cache storage section. All stack frames of user programs to be executed on a time-shared basis are stored in the first section, so cache misses due to stack operations are avoided. An instruction cache having various categories of instructions stores a group of status bits identifying the instruction category with each instruction.

Abstract: A multiprocessing system includes a cache coherency technique that ensures that every access to a line of data is the most up-to-date copy of that line without storing cache coherency status bits in a global memory and any reference thereto. An operand cache includes a first directory which directly, on a one-to-one basis maps a range of physical address bits into a first section of the operand cache storage. An associative directory multiply maps physical addresses outside of the range into a second section of the operand cache storage section. All stack frames of user programs to be executed on the time-shared basis are stored in the first section, so cache misses due to stack operations are avoided. An instruction cache haivng various categories of instructions stores a group of status bits identifying the instruction category with each instruction.