Abstract: A computer system is presented implementing a system and method for properly ordering write operations. The system and method for properly ordering write operations aids in maintaining memory coherency within the computer system. The computer system includes multiple interconnected processing nodes. One or more of the processing nodes includes a central processing unit (CPU) and/or a cache memory, and one or more of the processing nodes includes a memory controller coupled to a memory. The CPU or cache generates a write command to store data within the memory. The memory controller receives the write command and responds to the write command by issuing a target done response to the CPU or cache after the memory controller: (i) properly orders the write command within the memory controller with respect to other commands pending within the memory controller, and (ii) determines that a coherency state with respect to the write command has been established within the computer system.

Abstract: A system and method for inputting a set of values, e.g. an operating frequency, using dual-use signal connections. In an exemplary computer system, one or more processors are each coupled to a bridge. The dual-use signal connections are used to input an operating frequency ratio to a processor. The operating frequency ratio may also be input to the bridge. Once the operation of the processor has been initialized, the dual-use signal connections may be used to output operating parameters of the processor. The use of the using dual-use signal connections may advantageously allow for the operating frequency ratio to be input to the processor without dedicated signal lines or pins.

Abstract: A messaging scheme that accomplishes cache-coherent data transfers during a memory read operation in a multiprocessing computer system is described. A source processing node sends a read command to a target processing node to read data from a designated memory location in a system memory associated with the target processing node. In response to the read command, the target processing node transmits a probe command to all the remaining processing nodes in the computer system regardless of whether one or more of the remaining nodes have a copy of the data cached in their respective cache memories. Probe command causes each node to maintain cache coherency by appropriately changing the state of the cache block containing the requested data and by causing the node having an updated copy of the cache block to send the cache block to the source node.

Abstract: A method and system of expediting issuance of a second request of a pair of ordered requests into a distributed coherent communication fabric. The first request of the ordered pair is issued into the coherent communication fabric and directed to a first target. Issuance of the second request into the coherent communication fabric is stalled until the first target receives and orders the first request and transmits a response acknowledging the same.

Abstract: A processor employing a post-cache (LS2) buffer. Loads are stored into the LS2 buffer after probing the data cache. The load/store unit snoops the loads in the LS2 buffer against snoop requests received from an external bus. If a snoop invalidate request hits a load within the LS2 buffer and that load hit in the data cache during its initial probe, the load/store unit scans the LS2 buffer for older loads which are misses. If older load misses are detected, a synchronization indication is set for the load misses. Subsequently, one of the load misses completes and the load/store unit transmits a synchronization signal with the status for the load miss. The processor synchronizes to the instruction corresponding to the load miss, thereby discarding load hit which was subsequently snoop hit. The discarding instructions are refetched and reexecuted, thereby causing the load hit to reexecute subsequent to an earlier load miss.

Abstract: A technique for managing register assignments. The technique involves maintaining, in a register list memory circuit having entries that respectively correspond to physical registers, a list of register assignments that assign logical registers to the physical registers. The technique further involves maintaining, in a vector memory circuit having bits that respectively correspond to the physical registers, a valid vector that forms, in combination with the list of register assignments, a list of valid register assignments. Furthermore, the technique involves storing, for an instruction that is mapped by the data processor, a copy of the valid vector from the vector memory circuit to a silo memory circuit. Preferably, the processor using the technique has the ability to execute branches of instructions speculatively, and to recover if it is determined that the processor executed down an incorrect instruction branch.

Abstract: A method and system of expediting issuance of a second request of a pair of ordered requests into a distributed coherent communication fabric. The first request of the ordered pair is issued into the coherent communication fabric and directed to a first target. Issuance of the second request into the coherent communication fabric is stalled until the first target receives and orders the first request and transmits a response acknowledging the same.

Abstract: A technique for handling a conditional move instruction in an out-of-order data processor. The technique involves detecting a conditional move instruction within an instruction stream, and generating multiple instructions according to the detected conditional move instruction. The technique further involves replacing the conditional move instruction within the instruction stream with the generated multiple instructions. The generated multiple instructions are generated such that each of the generated multiple instructions executes using no more than two input ports of an execution unit. The generated multiple instructions include a first generated instruction that produces a condition result indicating whether a condition exists, and a second generated instruction that inputs the condition result as a portion of an operand which identifies a register of the out-of-order data processor.

Abstract: A method and apparatus for controlling power management state transitions between two devices, e.g., a processor and a bus bridge, that are connected through a clock forwarded interface bus in a computer system. The bus bridge is configured to coordinate disconnection of the processor from the interface. Particularly, the bus bridge may use a fist signal to indicate whether or not the processor is to be disconnected from the interface (e.g. a CONNECT signal) and the processor may use a second signal to indicate whether or not the processor is to be disconnected from the interface (e.g. a PROCREADY signal). The processor is disconnected from the interface responsive to both the first signal and the second signal indicating that the processor is to be disconnected. The signals may also be used to reconnect the processor to the interface.

Abstract: An apparatus and method for superforwarding load operands in a microprocessor are provided. An execution unit in a microprocessor is configured to receive a load instruction and a subsequent instruction. If the load instruction corresponds to a simple load instruction, a destination operand of the load instruction can be superforwarded to a subsequent instruction if the subsequent instruction specifies a source operand that depends on the destination operand of the load instruction. The subsequent instruction is not required to wait until a load instruction executes or completes and can be scheduled and/or executed prior to or at the same time as the load instruction. Consequently, latencies associated with operand dependencies may be reduced.

Abstract: A technique for handling a conditional move instruction in an out-of-order data processor. The technique involves detecting a conditional move instruction within an instruction stream, and generating multiple instructions according to the detected conditional move instruction. The technique further involves replacing the conditional move instruction within the instruction stream with the generated multiple instructions. The generated multiple instructions are generated such that each of the generated multiple instructions executes using no more than two input ports of an execution unit. The generated multiple instructions include a first generated instruction that produces a condition result indicating whether a condition exists, and a second generated instruction that inputs the condition result as a portion of an operand which identifies a register of the out-of-order data processor.

Abstract: A system and method for using a toggle command for setting and releasing a lock, i.e. a locktoggle. In an exemplary computer system, one or more processors are each coupled to a bus bridge through separate high speed connections, such as a pair of uni-directional address buses with respective source-synchronous clock lines and a bi-directional data bus with attendant source-synchronous clock lines. The locktoggle command is used to transmit both a lock request and an unlock request from a processor to a system coherency. point, e.g. the bus bridge. The system coherency point acknowledges when the lock has been established or released. While the lock is active, other processors are inhibited. from accessing at least the memory locations for which the lock was initiated. Locks are thus established at the system coherency point, which may advantageously allow for locking functionality in a non-shared bus system.

Abstract: A method for initializing a computing system comprising a plurality of devices which communicate on a communication link comprising a plurality of independent point-to-point links is provided, each of the point-to-point links interconnecting a respective pair of the plurality of devices. The method includes a link initialization procedure comprising initially configuring each respective pair of devices to communicate on the respective interconnecting link using common communication parameters, including a common frequency and a common link width. The link initialization procedure also may include an optimization procedure for determining maximum communication parameters for each interconnected pair of devices. If the maximum compatible parameters differ from the common parameters for any pair of devices, then the pair of devices may be reconfigured to communicate on the interconnecting link using the maximum compatible parameters.

Abstract: A method for initializing a computing system comprising a plurality of devices which communicate on a communication link comprising a plurality of independent point-to-point links is provided, each of the point-to-point links interconnecting a respective pair of the plurality of devices. The method includes a link initialization procedure comprising initially configuring each respective pair of devices to communicate on the respective interconnecting link using common communication parameters, including a common frequency and a common link width. The link initialization procedure also may include an optimization procedure for determining maximum communication parameters for each interconnected pair of devices. If the maximum compatible parameters differ from the common parameters for any pair of devices, then the pair of devices may be reconfigured to communicate on the interconnecting link using the maximum compatible parameters.

Abstract: A processor is configured, upon losing sufficient ownership of a cache block to complete a memory operation, to “backoff” for a backoff time interval. During the backoff time interval, the processor does not attempt to reestablish ownership of the cache block. Once the backoff time interval expires, the processor reestablishes ownership of the cache block. If the ownership is lost again before completing the memory operation, the processor is configured to increase the backoff time interval. In one embodiment, the processor is configured to increase the backoff time at an exponential rate. Accordingly, when two or more processors are attempting to obtain ownership of one or more cache blocks to complete a memory operation, the backoff time interval may eventually increase to an interval which allows one of the processors to complete the memory operation. Other ones of the two or more processors may subsequently complete their memory operations. Deadlock may therefore be avoided.

Abstract: A system and method for transferring data from a first clock domain to a second clock domain wherein a clock skipping technique is employed to maintain the same level of data throughput in the transmitting and receiving domains. In one embodiment, a plurality of serial data values are received from a device in the first clock domain and are stored in a plurality of flip-flops. The data values are clocked into the flip-flops, one value per flip-flop, at a first clock rate corresponding to the first clock domain. After a value is stored in the last flip-flop, the cycle is repeated and the previously stored values are overwritten. The data values are retrieved from the flip-flops after the values have had time to stabilize, but before they are overwritten. The values are retrieved at a second clock rate corresponding to a second clock domain and are transferred to a device in the second clock domain.

Abstract: A system and method for transferring a data stream between devices having different clock domains. The method initiates a serial data stream between a transmitter and a receiver. The transmitter operates according to a first clock having a first clock rate, and the receiver operates according to a second clock having a second clock rate. A ratio between the second clock rate and the first clock rate is an integer number greater than or equal to one. A first state is provided over a serial line between the transmitter and the receiver One or more start bits are provided over the serial line. The start bits indicate a second state different from the first state. One or more ratio bits are provided over the serial line after the start bit. The ratio bits indicate the ratio between the second clock rate and the first clock rate. The start bits are received. Using a transition between the first state and the second state evident in receiving each of the start bits, the ratio bits are received.

Abstract: A method for implementing interrupt requests in a computing system comprising a plurality of processing devices interconnected by a plurality of point-to-point links is provided. An interrupt request is broadcast on the point-to-point links to each of the plurality of processing devices. Each processing device is configured to decode the interrupt request to determine whether the processing device is a target of the interrupt request. Each processing device transmits a response to acknowledge receipt of the interrupt request, regardless of whether the processing device is a target of the interrupt request. If the interrupt request is an arbitrated request, each processing device also is configured to respond to the interrupt request with priority information. A processing device is then selected to service the arbitrated request based on the priority information.

Abstract: A technique for managing register assignments. The technique involves maintaining, in a register list memory circuit having entries that respectively correspond to physical registers, a list of register assignments that assign logical registers to the physical registers. The technique further involves maintaining, in a vector memory circuit having bits that respectively correspond to the physical registers, a valid vector that forms, in combination with the list of register assignments, a list of valid register assignments. Furthermore, the technique involves storing, for an instruction that is mapped by the data processor, a copy of the valid vector from the vector memory circuit to a silo memory circuit. Preferably, the processor using the technique has the ability to execute branches of instructions speculatively, and to recover if it is determined that the processor executed down an incorrect instruction branch.

Abstract: A microprocessor with a floating point unit configured to rapidly execute floating point load control word (FLDCW) type instructions in an out of program order context is disclosed. The floating point unit is configured to schedule instructions older than the FLDCW-type instruction before the FLDCW-type instruction is scheduled. The FLDCW-type instruction acts as a barrier to prevent instructions occurring after the FLDCW-type instruction in program order from executing before the FLDCW-type instruction. Indicator bits may be used to simplify instruction scheduling, and copies of the floating point control word may be stored for instruction that have long execution cycles. A method and computer configured to rapidly execute FLDCW-type instructions in an out of program order context are also disclosed.