Electrical computers and digital data processing systems: input/ – Input/output data processing – Concurrent input/output processing and data transfer
Reexamination Certificate
1998-10-19
2001-02-06
Lee, Thomas C. (Department: 2782)
Electrical computers and digital data processing systems: input/
Input/output data processing
Concurrent input/output processing and data transfer
C710S001000, C710S005000, C710S007000, C710S014000, C710S032000, C710S061000, C709S241000, C712S225000, C712S245000, C714S707000
Reexamination Certificate
active
06185632
ABSTRACT:
The present invention generally relates to communication protocols, and more specifically to a high speed image communication protocol using an IEEE 1394 bus. An IEEE 1394 standard, also known in industry as fire wire, describes a high speed serial bus that contains a 64 bit address space. The 1394 bus is a shared memory architecture, not a network or an I/O channel, and is incorporated herein by reference. The 64 bit address is divided into 16 bits for a node ID, e.g., a node number and bus number, and 48 bits for a memory space and command and status registers (CSR). The CSR allows read/write/lock operations used for asynchronous data communication that conforms to ISO 13213/IEEE 1212 CSR standard, which is incorporated herein by reference. Asynchronous communication is not guaranteed with respect to time, i.e., the user cannot determine when the data will transfer.
In addition to asynchronous communication, the IEEE 1394 serial bus provides for isochronous data communication. Isochronous communication guarantees both a latency, i.e., delay, and a bandwidth of data, with respect to time. For example, every 125 microseconds a data packet that matches a predetermined bandwidth in length, is transmitted to an isochronous channel. Importantly, unlike asynchronous data packets, isochronous data packets can be sent to hardware without microprocessor intervention.
While the IEEE 1394 standard offers both asynchronous and isochronous communication, no known protocols exist that take advantage of these features for communication of a link layer controller and a physical layer. Protocols provide a mechanism to enable communication between two or more devices, such as a copier, a printer, and a scanner. One such protocol is serial bus protocol
2
(SBP-
2
) only defines an asynchronous data transfer communication protocol. SBP-
2
, which is incorporated herein by reference, requires that an initiator login to a target to begin a communication. Basic building blocks of SBP-
2
include operation request block (ORB) data structures. Two main types of ORBs are a command ORB and a management ORB. Additionally, SBP-
2
describes services that operate on the command and management ORBs as fetch agents.
A problem exists since SBP-
2
's use of fetch agents is inefficient for some data transfers, such as requests and replies. For example, initially, the fetch agent must fetch the ORB to learn an address of data. After learning the data address, the fetch agent reads the data using 1394 read transactions. An initial device must manage the ORBs stored in a linked list. Thus, the initial device writes an address of a first ORB in the list to a doorbell register to inform a target device where to begin. When the ORB is completed, the target device writes a status back to the initial device's memory. Thus, the cost is high in terms of resources and time when sending only small packets of control data. Another problem with using SBP-
2
is that SBP-
2
does not specify a way to transfer isochronous data. Early versions of the standard did specify a means for isochronous data transfer, however, isochronous data transfer was removed due to the complexity.
Problems also exist with solutions such as an IEC 61883 standard function control protocol (FCP). FCP is typically used with audio/video devices for isochronous data transfer, however, it only handles point to point connections between two devices. Additionally, FCP, which defines command and response frames, can only be sent to a fixed address with a fixed length. Thus, commands and responses are overwritten when multiple devices or the same device write to the fixed address before information is processed. Other solutions include utilizing a small computer systems interface (SCSI) and an IEEE 1284 parallel port. The parallel port, however, falls short on performance and fails to offer isochronous data transfer. Additionally, SCSI lacks isochronous data transfer which is a key element in allowing for a low cost hardware transmission.
Accordingly, it is a primary object of the present invention to provide an improved method to enable communication between two or more devices.
Another object of the present invention is to provide an improved method for reducing high overhead of basic protocol functions such as requests and replies.
Yet another object of the present invention is to provide an improved method which allows for an isochronous data transfer.
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Hewlett--Packard Company
Lee Thomas C.
Nguyen Tanh
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