LSI53C875 LSI Logic, LSI53C875 Datasheet - Page 202

• Manufacturer Part Number: LSI53C875
• Description: PCI to Ultra SCSI I/O Processor
• Manufacturer: LSI Logic

6-6
Instruction Set of the I/O Processor
Note:
Note:
Do not use indirect and table indirect addressing
simultaneously; use only one addressing method at a time.
Do not use indirect and table indirect addressing
simultaneously; use only one addressing method at a time.
Once the data pointer address is loaded, it is executed
as when the chip operates in the direct mode. This
indirect feature allows a table of data buffer addresses to
be specified. Using the LSI Logic SCSI SCRIPTS
assembler, the table offset is placed in the script at
compile time. Then at the actual data transfer time, the
offsets are added to the base address of the data
address table by the external processor. The logical I/O
driver builds a structure of addresses for an I/O rather
than treating each address individually. This feature
makes it possible to locate SCSI SCRIPTS in a PROM.
Table Indirect
When this bit is set, the 24-bit signed value in the start
address of the move is treated as a relative displacement
from the value in the
register. Both the transfer count and the
source/destination address are fetched from this location.
Use the signed integer offset in bits [23:0] of the second
four bytes of the instruction, added to the value in the
Data Structure Address (DSA)
byte count and then the data address. The signed value
is combined with the data structure base address to
generate the physical address used to fetch values from
the data structure. Sign extended values of all ones for
negative values are allowed, but bits [31:24] are ignored.
Figure 6.2
Don’t Care
Command
illustrates the Block Move Instruction register.
Data Structure Address (DSA)
Table Offset
register, to fetch first the
Not Used
28