Abstract: A memory system provides data error detection and correction and address error detection. A cyclical-redundancy-check (CRC) code generates address check bits. A 32-bit address is compressed to 6 address check bits using the CRC code. The 6 address check bits are concatenated with 64 data bits and 2 flag bits to generate a 72-bit check word. The 72-bit check word is input to an error-correction code (ECC) generator that generates 12 check bits that are stored in memory with the 64 data bits. A 76-bit memory module can store the 64 data and 12 check bits. Nibble errors can be corrected, and all nibble+1 bit errors can be detected. Also, a 6-bit error in a sequence of bits can be detected. This allows all errors in the 6-bit CRC of the address to be detected. The CRC code and ECC are ideal for detecting double-bit errors common with multiplexed-address DRAMs.

Abstract: A write-back cache has error-correction code (ECC) fields storing ECC bits for cache lines. Clean cache lines are re-fetched from memory when an ECC error is detected. Dirty cache lines are corrected using the ECC bits or signal an uncorrectable error. The type of ECC code stored is different for clean and dirty lines. Clean lines use an error-detection code that can detect longer multi-bit errors than the error correction code used by dirty lines. Dirty lines use a correction code that can correct a bit error in the dirty line, while the detection code for clean lines may not be able to correct any errors. Dirty lines' ECC is optimized for correction while clean lines' ECC is optimized for detection. A single-error-correction, double-error-detection (SECDED) code may be used for dirty lines while a triple-error-detection code is used for clean lines.

Abstract: A memory system provides data error detection and correction and address error detection. A cyclical-redundancy-check (CRC) code generates address check bits. A 32-bit address is compressed to 6 address check bits using the CRC code. The 6 address check bits are concatenated with 64 data bits and 2 flag bits to generate a 72-bit check word. The 72-bit check word is input to an error-correction code (ECC) generator that generates 12 check bits that are stored in memory with the 64 data bits. A 76-bit memory module can store the 64 data and 12 check bits. Nibble errors can be corrected, and all nibble+1 bit errors can be detected. Also, a 6-bit error in a sequence of bits can be detected. This allows all errors in the 6-bit CRC of the address to be detected. The CRC code and ECC are ideal for detecting double-bit errors common with multiplexed-address DRAMs.

Abstract: A memory system provides data error detection and correction and address error detection. A cyclical-redundancy-check (CRC) code generates address check bits. A 32-bit address is compressed to 6 address check bits using the CRC code. The 6 address check bits are concatenated with 64 data bits and 2 flag bits to generate a 72-bit check word. The 72-bit check word is input to an error-correction code (ECC) generator that generates 12 check bits that are stored in memory with the 64 data bits. A 76-bit memory module can store the 64 data and 12 check bits. Nibble errors can be corrected, and all nibble+1 bit errors can be detected. Also, a 6-bit error in a sequence of bits can be detected. This allows all errors in the 6-bit CRC of the address to be detected. The CRC code and ECC are ideal for detecting double-bit errors common with multiplexed-address DRAMs.

Abstract: A multi-processor, multi-cache system has filter pipes that store entries for request messages sent to a central coherency controller. The central coherency controller orders requests from filter pipes using coherency rules but does not track completion of invalidations. The central coherency controller reads snoop tags to identify sharing caches having a copy of a requested cache line. The central coherency controller sends an ordering message to the requesting filter pipe. The ordering message has an invalidate count indicating the number of sharing caches. Each sharing cache receives an invalidation message from the central coherency controller, invalidates its copy of the cache line, and sends an invalidation acknowledgement message to the requesting filter pipe. The requesting filter pipe decrements the invalidate count until all sharing caches have acknowledged invalidation.

Abstract: Power management for a multi-processor chip includes a centralized global power manager that monitors global power for the whole chip, and local power managers. Local power managers manage power for local blocks such as processor cores, caches, and memory controllers. When a local block executes an instruction or accesses memory, an event is generated and looked up in a local power estimate table. A local power estimate for that event is sent to the global power manager, which sums all local power estimates received from all local blocks. An exponential moving average (EMA) is generated and compared to a global power threshold. When global power is over the threshold, local targets are sent to power managers that generate and monitor local power averages that must remain under the local target. The local block is throttled by the local power manager to reduce power when the local target is exceeded.

Abstract: A system chip has many local blocks including processor cores, caches, and memory controllers. Each local block has a local sample-select mux that is controlled by a local selection control register. The mux selects from among hundreds of internal sample nodes in the local block, and can also pass through samples output by an upstream local block. The selected samples from local blocks are sent to a central on-chip logic analyzer that compares the samples to a maskable trigger value. When the trigger value is matched, a trigger state machine advances, and samples are stored into a central capture buffer. A user debugging the chip can later read out the central capture buffer at a slower speed. Thousands of internal nodes from local blocks can be selected for sampling, triggering, and debugging. Local blocks include valid bits in 64-bit-wide samples. Only valid samples are written to the capture buffer.

Abstract: A memory system provides data error detection and correction and address error detection. A Single-byte Error-Correcting/Double-byte Error-Detecting (SbEC/DbED) code with the byte being a 4-bit nibble is used to detect up to 8-bit errors and correct data errors of 4 bits or less. Rather than generating address parity, which is poor at detecting even numbers of errors, a cyclical-redundancy-check (CRC) code generates address check bits. A 32-bit address is compressed to just 4 address check bits using the CRC code. The 4 address check bits are merged (XOR'ed) with two 4-bit nibbles of the data SbEC/DbED code to generate a merged ECC codeword that is stored in memory. An address error causes a 2-nibble mis-match due to the redundant merging of the 4 address check bits with 2 nibbles of data correction code. The CRC code is ideal for detecting even numbers of errors common with multiplexed-address DRAMs.

Abstract: In an embodiment, present application describes a system and method to detect the alignment of multiple clocks in multi-clock domains system. In some variations, multiple clocks are derived from one or more reference clocks using various PLLs. The derived clocks maintain frequency relationship with the reference clock. In some variations, a relationship between the frequencies of various clocks is used to generate the alignment signals in the domain of one of the clocks.

Abstract: In an embodiment, present application describes a system and method to detect the alignment of multiple clocks in multi-clock domains system. In some variations, multiple clocks are derived from one or more reference clocks using various PLLs. The derived clocks maintain frequency relationship with the reference clock. In some variations, a relationship between the frequencies of various clocks is used to generate the alignment signals in the domain of one of the clocks.

Abstract: A single-chip central processing unit (CPU) includes a processing core and a complete cache-coherent I/O system that operates asynchronously with the processing core. An internal communications protocol uses synchronizers and data buffers to transfer information between a clock domain of the processing core and a clock domain of the I/O system. The synchronizers transfer control and handshake signal between clock domains, but the data buffer transfers data without input or output synchronization circuitry for data bits. Throughput for the system is high because the processing unit has direct access to I/O system so that no delays are incurred for complex mechanisms which are commonly employed between a CPU and an external I/O chip-set. Throughput is further increased by holding data from one DMA transfer in the data buffer for use in a subsequent DMA transfer.

Abstract: A multiprocessor system includes a plurality of central processing units (CPUs) connected to one another by a system bus. Each CPU includes a cache controller to communicate with its cache, and a primary memory controller to communicate with its primary memory. When there is a cache miss in a CPU, the cache controller routes an address request for primary memory directly to the primary memory via the CPU as a speculative request without access the system bus, and also issues the address request to the system bus to facilitate data coherency. The speculative request is queued in the primary memory controller, which in turn retrieves speculative data from a specified primary memory address. The CPU monitors the system bus for a subsequent transaction that requests the specified data in the primary memory. If the subsequent transaction requesting the specified data is a read transaction that corresponds to the speculative address request, the speculative request is validated and becomes non-speculative.

Abstract: The main cache of a processor in a multiprocessor computing system is coupled to receive writeback data during writeback operations. In one embodiment, during writeback operations, e.g., for a cache miss, dirty data in the main cache is merged with modified data from an associated write cache, and the resultant writeback data line is loaded into a writeback buffer. The writeback data is also written back into the main cache, and is maintained in the main cache until replaced by new data. Subsequent requests (i.e., snoops) for the data are then serviced from the main cache, rather than from the writeback buffer. In some embodiments, further modifications of the writeback data in the main cache are prevented. The writeback data line in the main cache remains valid until read data for the cache miss is returned, thereby ensuring that the read address reaches the system interface for proper bus ordering before the writeback line is lost.

Abstract: A phase-enable circuit clocks a first functional unit at a first frequency and a second functional unit at a second frequency. Each of the first and second functional units is provided with a first clock signal of the first frequency. A phase-enable generator then uses the first clock signal and a second clock signal of a second frequency lower than the first frequency to develop a phase-enable signal that periodically disables a clock input terminal of the second functional unit so that the second functional unit is clocked at the second frequency. Changing the frequency of the second clock to zero switches the phase-enable circuit into another mode of operation. In that mode, the clock input terminal of the second functional unit is constantly enabled and the first and second functional units are each clocked at the first frequency.

Abstract: A synchronizer comprised in part of a series of flip-flops is used to deterministically transfer data between clock domains during system test. Flip-flops in the clock domain operating at a higher clock frequency have a clock enable signal. The clock enable signal is defined so as to approximately align the enabled rising clock edges of the faster clock signal with the falling edges of the slower clock signal. This approximate alignment provides a timing window of one half period of the slower clock for the data to stabilize at the input of a flip-flop in the faster clock domain before it is sampled. This ensures deterministic transfer of data. Data flow control circuitry can be used to provide a ready signal to the faster clock domain to indicate that the synchronizer is available to transfer a synchronization signal. After testing is complete, the synchronizer can operate in an application mode wherein one or more of the clock enable signals is set to a continuous high level to minimize latency.

Abstract: This invention describes a link-by-link flow control method for packet-switched uniprocessor and multiprocessor computer systems that maximizes system resource utilization and throughput, and minimizes system latency. The computer system comprises one or more master interfaces, one or more slave interfaces, and an interconnect system controller which provides dedicated transaction request queues for each master interface and controls the forwarding of transactions to each slave interface. The master interface keeps track of the number of requests in the dedicated queue in the system controller, and the system controller keeps track of the number of requests in each slave interface queue. Both the master interface, and system controller know the maximum capacity of the queue immediately downstream from it, and does not issue more transaction requests than what the downstream queue can accommodate.

Abstract: An apparatus and method for handling interrupt requests from any of a plurality of interrupters to any of a plurality of interrupt handlers. Each interrupt handler includes an interrupt input request queue for holding a plurality of incoming interrupt requests. A system controller is connected to the interrupters and the interrupt handlers, and includes an input queue coupled to each interrupter for receiving a plurality of interrupt requests. The system controller includes a processor and a memory storing instructions for controlling its operation. The system controller also includes an output queue coupled to each interrupt handler (which in many cases will also be interrupters), and a counter for monitoring the current number, at any given time, of interrupt requests pending in each of the interrupt input queues in the interrupt handlers.

Abstract: A single-chip central processing unit (CPU) includes a processing core and a complete cache-coherent I/O system that operates asynchronously with the processing core. An internal communications protocol uses synchronizers and data buffers to transfer information between a clock domain of the processing core and a clock domain of the I/O system. The synchronizers transfer control and handshake signal between clock domains, but the data buffer transfers data without input or output synchronization circuitry for data bits. Throughput for the system is high because the processing unit has direct access to I/O system so that no delays are incurred for complex mechanisms which are commonly employed between a CPU and an external I/O chip-set. Throughput is further increased by holding data from one DMA transfer in the data buffer for use in a subsequent DMA transfer.

Abstract: The present invention provides a scalable, modular and pipelined distributed bus arbitration system for efficiently resolving bus contention between sub-systems, e.g., processors, coupled to a common system bus. The arbitration system includes a plurality of distributed bus arbiters which receives the bus requests from the sub-systems and independently determine the next bus master. The arbitration protocol enables the arbitration process to be eliminated from the critical timing path thereby allowing the system to operate at the maximum system clock frequency possible for a given integrated circuit (IC) technology to reduce overall system clock latencies. Any change among the sub-systems during an arbitration clock cycle is based on any system bus request(s) which are active during a clock cycle immediately preceding the arbitration clock cycle, and is independent of any system bus request(s) asserted during the arbitration clock cycle. In addition, the arbitration protocol treats a current bus master, i.e.

Abstract: Bi-directional data transfers between a first system and a second system, which have asynchronous clock domains, are performed using a single dual-port memory. A direction control circuit, which is connected between the first and second systems, determines the desired direction of data transfer and generates one or more direction signals representative of this direction. A write control circuit is coupled to receive a direction control signal, as well as write control signals from the first and second systems. Similarly, a read control signal is coupled to receive a direction control signal, as well as read control signals from the first and second systems. If data transfer is to proceed from the first system to the second system, the write control circuit gives the first system control over the write port of the dual-port memory, and the read control circuit gives the second system control over the read port of the dual-port memory in response to the direction control signals.