Broadcast command packet protocol for SCSI interface
AssigneeAdaptec, Inc.
InventorMichael T. Kosco
Life of this patent
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Abstract
A broadcast command packet protocol provides for significant reduction of the overhead associated with a data transfer operation and the consequent increase in throughput efficiency. IDENTIFY and SIMPLE TAG messages, along with a command descriptor block, are collapsed into a 24-byte packet which is broadcast to all target devices residing on a bus in a “burst” subsequent to an arbitration and a NULL SELECT phase. Multiple broadcast command packets are sequentially burst onto the data bus in back-to-back fashion, to one or more target devices subsequent to a single arbitration phase. Each target device verifies its own ID, queues up its intended commands, and subsequently arbitrates for control of the bus to executed the commands.
Claims15
In an SCSI protocol, in which an initiator device arbitrates for control of an SCSI bus in order to provide message and command data to a target device, a method for reducing protocol overhead with respect to message and command transmissions, comprising the steps of:
- providing a NULL SELECT command including an ATN signal in combination with null values on all data signals on a data bus;
- broadcasting a command packet, the command packet including an information payload, the command packet further including an IDENTIFY MESSAGE and TAG MESSAGE, such that the command packet collapses an IDENTIFY and SIMPLE TAG message into a command descriptor block so as to define a packet;
- and
- wherein each respective one of a multiplicity of target devices residing on an SCSI bus, simultaneously receive said command packet, each respective one of the multiplicity of target devices reading a target ID field in order to determine whether it is the intended recipient of said command packet.
In an SCSI protocol, in which IDENTIFY and SIMPLE TAG messages are collapsed along with a command descriptor block into a broadcast command packet, the broadcast command packet being subsequently broadcast to a multiplicity of target devices residing on an SCSI bus in a burst subsequent to an arbitration, the broadcast command packet comprising:
- a target ID byte and an initiator ID byte;
- an IDENTIFY message byte;
- a queue TAG message byte and a queue TAG value byte;
- a packet payload;
- and
- an indicator bit for defining whether the content of the packet payload comprises a command descriptor block or comprises messages.
In an SCSI protocol, in which IDENTIFY and SIMPLE TAG messages are collapsed along with a command descriptor block into a broadcast command packet, the broadcast command packet being subsequently broadcast to a multiplicity of target devices residing on an SCSI bus in a burst subsequent to an arbitration, a system for reducing protocol overhead with respect to message and command transmission, comprising:
- a broadcast command packet including;
- a target ID byte and an initiator byte;
- an IDENTIFY message byte;
- a queue TAG message byte and a queue TAG value byte;
- a packet payload;
- and
- an INDICATOR bit for defining whether the content of the packet payload comprises a command descriptor block or comprises messages;
- and
- wherein each respective one of a multiplicity of target devices residing on the SCSI bus simultaneously receive said command packet, each respective one of the multiplicity of target devices reading the target ID byte in order to determine whether it is the intended recipient of said command packet.
Dependencies are inferred from the claim text.