Avago Technologies LSI53C895A User Manual

Page 230

5-8

SCSI SCRIPTS Instruction Set

After a Table Indirect opcode is fetched, the DSA is
added to the 24-bit signed offset value from the opcode
to generate the address of the required data; both
positive and negative offsets are allowed. A subsequent
fetch from that address brings the data values into the
chip.

For a MOVE instruction, the 24-bit byte count is fetched
from system memory. Then the 32-bit physical address is
brought into the LSI53C895A. Execution of the move
begins at this point.

SCRIPTS can directly execute operating system I/O data
structures, saving time at the beginning of an I/O
operation. The I/O data structure can begin on any
longword boundary and may cross system segment
boundaries.

There are two restrictions on the placement of pointer
data in system memory:

•

The eight bytes of data in the MOVE instruction must
be contiguous, as shown below, and

•

Indirect data fetches are not available during
execution of a Memory-to-Memory DMA operation.

OPC

OpCode

This 1-bit OpCode field defines the type of Block Move
(MOVE) Instruction to be preformed in Target and Initiator
mode.

Target Mode

In Target mode, the OpCode bit defines the following
operations:

Byte Count

Physical Data Address

OPC

Instruction Defined

MOVE/MOVE64

CHMOV/CHMOV64