Systems, methods, and apparatus for improving bus latency are described. A method performed at a device coupled to a serial bus includes using a dynamic identifier in a first transaction conducted over a first serial bus. The dynamic identifier includes unique identifier and variable identifier portions. The device participates in a sequence of bus arbitrations until the slave device gains access to the first serial bus or a second serial bus. The value of the variable identifier portion may be increased after each bus arbitration that does not result in a grant of access to the first serial bus, and cleared after each bus arbitration that results in a grant of access to the first serial bus. A second transaction may be conducted over the first serial bus after gaining access to the first serial bus. The value of the dynamic identifier defines slave device priority for bus arbitrations.

Systems, methods, and apparatus for improving bus latency are described. A method performed at a device coupled to a serial bus includes using a dynamic identifier in a first transaction conducted over a first serial bus. The dynamic identifier includes unique identifier and variable identifier portions. The device participates in a sequence of bus arbitrations until the slave device gains access to the first serial bus or a second serial bus. The value of the variable identifier portion may be increased after each bus arbitration that does not result in a grant of access to the first serial bus, and cleared after each bus arbitration that results in a grant of access to the first serial bus. A second transaction may be conducted over the first serial bus after gaining access to the first serial bus. The value of the dynamic identifier defines slave device priority for bus arbitrations.

A method for self-moderating bus arbitration for access to a common bus is provided. The method may include receiving, by a bus arbiter, a request from a master device, wherein the received request includes a priority value set by the master device. The method may also include identifying the priority value from the received transaction request. The method may then include determining an insertion point within a priority table based on comparing the identified priority value to a table entry priority value associated with each table entry within the priority table. The method may further include inserting a new entry into the priority table based on the determined insertion point. The method may also include identifying a highest priority entry within the priority table. The method may then include serving the identified highest priority entry.

A method for self-moderating bus arbitration for access to a common bus is provided. The method may include receiving, by a bus arbiter, a request from a master device, wherein the received request includes a priority value set by the master device. The method may also include identifying the priority value from the received transaction request. The method may then include determining an insertion point within a priority table based on comparing the identified priority value to a table entry priority value associated with each table entry within the priority table. The method may further include inserting a new entry into the priority table based on the determined insertion point. The method may also include identifying a highest priority entry within the priority table. The method may then include serving the identified highest priority entry.

An arbitration system receives requests to access a destination during an arbitration window that spans multiple processor clock cycles. During each clock cycle, the destination is monitored to determine whether the destination is suffering from backpressure by receiving more requests than the destination is able to accommodate during the clock cycle. In response to detecting backpressure, a masking index value assigned to a requesting source is incremented, which limits an amount of requests from the source that will be granted destination access during a subsequent arbitration window. Alternatively, in response to detecting an absence of backpressure during an arbitration window, the masking index value is decremented, which increases the amount of requests from the source that will be granted destination access during a subsequent arbitration window. This arbitration process continues for successive arbitration windows, oscillating between incrementing and decrementing the masking index value during the successive arbitration windows.

An arbitration system receives requests to access a destination during an arbitration window that spans multiple processor clock cycles. During each clock cycle, the destination is monitored to determine whether the destination is suffering from backpressure by receiving more requests than the destination is able to accommodate during the clock cycle. In response to detecting backpressure, a masking index value assigned to a requesting source is incremented, which limits an amount of requests from the source that will be granted destination access during a subsequent arbitration window. Alternatively, in response to detecting an absence of backpressure during an arbitration window, the masking index value is decremented, which increases the amount of requests from the source that will be granted destination access during a subsequent arbitration window. This arbitration process continues for successive arbitration windows, oscillating between incrementing and decrementing the masking index value during the successive arbitration windows.

A computer program product, according to one embodiment, includes a computer readable storage medium having program instructions embodied therewith. The computer readable storage medium is not a transitory signal per se. Moreover, the program instructions are readable and/or executable by a controller to cause the controller to perform a method which includes: receiving a same input/output request along more than one communication paths, and evaluating a workload associated with each of the communication paths. A communication path having a lowest workload associated therewith is selected. Moreover, information corresponding to the input/output request as well as a status are sent along the selected communication path. The status sent indicates that the selected communication path was chosen to satisfy the input/output request. A special status indicating that none of the remaining communication paths were chosen to satisfy the input/output request is also sent along each of the remaining communication paths.

A computer program product, according to one embodiment, includes a computer readable storage medium having program instructions embodied therewith. The computer readable storage medium is not a transitory signal per se. Moreover, the program instructions are readable and/or executable by a controller to cause the controller to perform a method which includes: receiving a same input/output request along more than one communication paths, and evaluating a workload associated with each of the communication paths. A communication path having a lowest workload associated therewith is selected. Moreover, information corresponding to the input/output request as well as a status are sent along the selected communication path. The status sent indicates that the selected communication path was chosen to satisfy the input/output request. A special status indicating that none of the remaining communication paths were chosen to satisfy the input/output request is also sent along each of the remaining communication paths.

Disclosed are methods and apparatus for multiplex operation of an electronic transmitting apparatus, comprising establishing logical channels between logical data producers and respective logical data consumers, the logical channels operable to pass data over a serial physical channel, constructing by a producer a payload, identifying a respective consumer, arbitrating use of the serial physical channel between logical channels to control sending of payloads, injecting a channel-specific logical protocol stop indicator into a data flow over the serial physical channel to instruct a receiving router to stop receipt of a previously started data flow and route the payload to a consumer, and sending at least a first uninterruptible data unit of the payload over the serial physical channel. Corresponding methods and apparatus are provided to enable a receiver to route payloads to consumers according to received logical protocol stop indicators.

Disclosed are methods and apparatus for multiplex operation of an electronic transmitting apparatus, comprising establishing logical channels between logical data producers and respective logical data consumers, the logical channels operable to pass data over a serial physical channel, constructing by a producer a payload, identifying a respective consumer, arbitrating use of the serial physical channel between logical channels to control sending of payloads, injecting a channel-specific logical protocol stop indicator into a data flow over the serial physical channel to instruct a receiving router to stop receipt of a previously started data flow and route the payload to a consumer, and sending at least a first uninterruptible data unit of the payload over the serial physical channel. Corresponding methods and apparatus are provided to enable a receiver to route payloads to consumers according to received logical protocol stop indicators.