and diagnostic procedures. In support of loopback diagnostics, the SCSI core can perform a self-selection and operate as both an initiator and a target.

The SCSI core is controlled by the integrated SCRIPTS processor through a high-level logical interface. Commands controlling the SCSI core are fetched out of the main host memory or local memory. These commands instruct the SCSI core to Select, Reselect, Disconnect, Wait for a Disconnect, Transfer Information, Change Bus Phases and, in general, implement all aspects of the SCSI protocol. The SCRIPTS processor is a special high-speed processor optimized for SCSI protocol.

2.1.1 DMA Core

The DMA core is a bus master DMA device that attaches directly to the industry standard PCI bus. The DMA core is tightly coupled to the SCSI core through the SCRIPTS processor, which supports uninterrupted scatter/gather memory operations.

The LSI53C810A supports 32-bit memory and automatically supports misaligned DMA transfers. An 80-byte FIFO allows 2, 4, 8, or 16 Dword bursts across the PCI bus interface to run efficiently without throttling the bus during PCI bus latency.

2.2 SCRIPTS Processor

The SCSI SCRIPTS processor allows both DMA and SCSI commands to be fetched from host memory. Algorithms written in SCSI SCRIPTS control the actions of the SCSI and DMA cores and are executed from 32-bit system RAM. The SCRIPTS processor executes complex SCSI bus sequences independently of the host CPU.

The SCRIPTS processor can begin a SCSI I/O operation in approximately 500 ns. This compares with 2–8 ms required for traditional intelligent host adapters. Algorithms may be designed to tune SCSI bus performance, to adjust to new bus device types (such as scanners, communication gateways, etc.), or to incorporate changes in the SCSI-2 or SCSI-3 logical bus definitions without sacrificing I/O performance. SCSI SCRIPTS are hardware independent, so they can be used interchangeably on any host or CPU system bus.

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Functional Description

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LSI 53C810A technical manual Scripts Processor, DMA Core