Broadcast command packet protocol for SCSI interface

• US 6,477,165 B1
• Filed: 06/16/1998
• Issued: 11/05/2002
• Est. Priority Date: 06/16/1997
• Status: Expired due to Term

• Current Assignee: PMC-Sierra Incorporated (Microchip Technology Incorporated)
• Original Assignee: Adaptec Incorporated (Steel Partners Holdings LP)
• Inventors: Kosco, Michael T.
• Primary Examiner(s): LUTHER, WILLIAM A
• Application Number:
  US09/097,899
• Time in Patent Office: 1,603 Days
• Field of Search: 370/389, 370/329, 370/253, 370/349, 370/328, 370/392, 370/471, 370/474, 370/390, 370/393, 370/397, 370/399, 370/414, 370/416, 370/418, 370/447, 370/409, 370/473, 370/475, 370/461, 370/462, 710/36, 710/39, 710/113, 710/119, 710/107, 710/128, 710/129
• US Class Current: 370/389
• CPC Class Codes: G06F 13/423 with synchronous protocol
• CPC Class Codes: G06F 2213/0036 Small computer system interface [SCSI]
• CPC Class Codes: H04L 12/18 for broadcast or conference , e.g. multicast

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.

Claims

1. 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.

2. The method according to claim 1, wherein the command packet is broadcast by an arbitration winning initiator device, the initiator and target devices coupled to an SCSI bus.

3. The method according to claim 2, wherein each target device capable of receiving broadcast command packets is identified as such by entering a broadcast command packet configuration identifier into each target device'"'"'s mode parameter page.

4. The method according to claim 3, the method including the step of configuring the SCSI bus to operate in broadcast command packet mode, the configuring step further comprising:

initiating a MODE SELECT operation, the initiator indicating the mode parameter page containing the broadcast command packet configuration identifier; and

identifying broadcast command packet capable devices by having capable devices transmit the broadcast command packet configuration identifier as an extension to a transfer width exponent code.

5. The method according to claim 4, wherein the broadcast command packet configuration identifier comprises a second nibble of the transfer width exponent code.

6. The method according to claim 4, further comprising broadcasting a multiplicity of command packets in sequential, back-to-back fashion, each broadcast command packet capable target device evaluating the bus contents and reading a target ID field of each broadcast command packet in order to determine if it is the intended recipient of said broadcast command packet.

7. The method according to claim 6, wherein a target device identifies a broadcast command packet as containing its address in the target ID field, the method further comprising:

receiving said broadcast command packet;

queuing said packet payload; and

issuing an REQ pulse to the initiator, thereby indicating receipt of said broadcast command packet.

8. The method according to claim 7, wherein the target device identified in a first broadcast command packet of a sequential broadcast places the SCSI bus into a data phase immediately at the completion of a broadcast command packet phase, the target device thereafter transferring data over the bus.

9. 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.

10. The broadcast command packet according to claim 9, the broadcast command packet comprising a 24-byte template, the packet payload comprising a 16-byte portion containing either an up to 16-byte command descriptor block or an up to 16-byte message block.

11. 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.

12. The system according to claim 11, wherein each target device capable of receiving broadcast command packets is identified as such by entering a broadcast command packet configuration identifier for each target device into a mode parameter page.

13. The system according to claim 12, wherein the SCSI bus is configured to operate in broadcast command packet mode by initiating a MODE SELECT operation, the initiator indicating the mode parameter page containing the broadcast command packet configuration identifier, each broadcast command packet capable target device identifying itself as such by transmitting the broadcast command packet configuration identifier as an extension to a transfer width exponent code in response to said MODE SELECT.

14. The system according to claim 13, wherein the broadcast command packet configuration identifier comprises a second nibble of the transfer width exponent code.

15. The system according to claim 14, wherein a target device identifies a broadcast command packet as containing its address in the target ID field, the target device receiving said broadcast command packet, queuing said packet payload, and issuing an REQ pulse to the initiator indicating receipt of said broadcast command packet.