LSI53C875 LSI Logic, LSI53C875 Datasheet - Page 200

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

6-4
The process repeats until the internally stored byte count has reached
zero. The LSI53C875 releases the PCI bus and then performs another
SCRIPTS instruction fetch cycle, using the incremented stored address
maintained in the
SCRIPTS instructions continues until an error condition occurs or an
interrupt SCRIPTS instruction is received. At this point, the LSI53C875
interrupts the host CPU and waits for further servicing by the host
system. It can execute independent Block Move instructions specifying
new byte counts and starting locations in main memory. In this manner,
the LSI53C875 performs scatter/gather operations on data without
requiring help from the host program, generating a host interrupt, or
requiring an external DMA controller to be programmed. An overview of
this process is presented in
Figure 6.1
Instruction Set of the I/O Processor
Move from cmd_buf, when CMD
Move from msg_in_buf, when MSG_IN
Select ATN 0, alt_addr
Move from identify_msg_buf, when MSG_OUT
Move from data_buf when DATA_OUT
Move from stat_in_buf, when STATUS
Move SCNTL2 & 7F to SCNTL2
Clear ACK
Wail disconnect alt2
Int 10
byte count
address
byte count
address
byte count
address
byte count
address
SCSI Initiator Write Example
Message Buffer
Command Buffer
Data Buffer
Status Buffer
System Processor
System Memory
SCRIPTS Overview
Table
DMA SCRIPTS Pointer (DSP)
Figure
6.1.
S
M
S
Y
S
E
B
U
T
SCRIPTS
Fetch
Write DSA
Write
DSP
Data
register. Execution of
LSI53C875
SCSI Bus