Abstract: A streamlined cache coherency protocol system and method for a multiple processor single chip device. There are three primary memory unit (e.g., a cache line) states (modified, shared, and invalid) and three intermediate memory unit pending states. The pending states are used by the present invention to prevent race conditions that may develop during the completion of a transaction. The pending states “lock out” the memory unit (e.g., prevent access by other agents to a cache line) whose state is in transition between two primary states, thus ensuring coherency protocol correctness. Transitions between states are governed by a series of request and reply or acknowledgment messages. The memory unit is placed in a pending state while appropriate measures are taken to ensure access takes place at an appropriate time. For example, a modification occurs only when other agents can not access the particular memory unit (e.g., a cache line).

Abstract: A streamlined cache coherency protocol system and method for a multiple processor single chip device. There are three primary memory unit (e.g., a cache line) states ( modified, shared, and invalid) and three intermediate memory unit pending states. The pending states are used by the present invention to prevent race conditions that may develop during the completion of a transaction. The pending states “lock out” the memory unit (e.g., prevent access by other agents to a cache line) whose state is in transition between two primary states, thus ensuring coherency protocol correctness. Transitions between states are governed by a series of request and reply or acknowledgment messages. The memory unit is placed in a pending state while appropriate measures are taken to ensure access takes place at an appropriate time. For example, a modification occurs only when other agents can not access the particular memory unit (e.g., a cache line).

Abstract: A cache coherent multiple processor integrated circuit. The circuit includes a plurality of processor units. The processor units are each provided with a cache unit. An embedded RAM unit is included for storing instructions and data for the processor units. A cache coherent bus is coupled to the processor units and the embedded RAM unit. The bus is configured to provide cache coherent snooping commands to enable the processor units to ensure cache coherency between their respective cache units and the embedded RAM unit. The multiple processor integrated circuit can further include an input output unit coupled to the bus to provide input and output transactions for the processor units. The bus is configured to provide split transactions for the processor units coupled to the bus, providing better bandwidth utilization of the bus. The bus can be configured to transfer an entire cache line for the cache units of the processor units in a single clock cycle, wherein the bus is 256 bits wide.

Abstract: Multiple processors are mounted on a single die. The die is connected to a memory storing multiple operating systems or images of multiple operating systems. Each of the processors or a group of one or more of the processors is operable to execute a distinct one of the multiple operating systems. Therefore, resources for a single operating system may be dedicated to one processor or a group of processors. Consequently, a large number of processors mounted on a single die can operate efficiently.

Abstract: An apparatus and method are shown for decoding variable length instructions in a processor where a line of variable length instructions from an instruction cache are loaded into an instruction buffer and the start bits indicating the instruction boundaries of the instructions in the line of variable length instructions is loaded into a start bit buffer. A first shift register is loaded with the start bits and shifted in response to a lower program count value which is also used to shift the instruction buffer. A length of a current instruction is obtained by detecting the position of the next instruction boundary in the start bits in the first register. The length of the current instruction is added to the current value of the lower program count value in order to obtain a next sequential value for the lower program count which is loaded into a lower program count register.