The SIOM and DIOM bits in the DMA Mode (DMODE) register determine whether the destination or source address of the instruction is in Memory space or I/O space, as illustrated in the following table. The Load and Store utilizes the PCI commands for I/O read and I/O write to access the I/O space.

 

 

 

 

 

 

 

 

 

Bit

 

Source

Destination

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SIOM (Load)

Memory

Register

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DIOM (Store)

Register

Memory

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5.8.1

 

First Dword

 

 

 

 

 

 

 

31

29

28

27 26 25 24 23 22

 

16 15

3

2

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DMA Command (DCMD)

 

 

 

DMA Byte Counter (DBC) Register

 

 

 

 

 

Register

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IT[2:0]

 

DSA

R

NF

LS

R

 

RA[6:0]

 

 

R

BC

 

1 1 1

x

0 0

x

x

0

x x x x x x x

0 0 0 0 0 0 0 0 0 0 0 0 0

x x x

 

 

 

 

 

 

IT[2:0]

Instruction Type

 

 

[31:29]

 

 

 

 

 

 

 

 

 

 

These bits should be 0b111, indicating the Load and

 

 

 

 

 

 

 

 

 

 

 

Store instruction.

 

 

 

 

 

 

 

 

 

 

DSA

DSA Relative

 

 

28

 

 

 

 

 

 

 

 

 

 

When this bit is cleared, the value in the DMA SCRIPTS

 

 

 

 

 

 

 

 

 

 

Pointer Save (DSPS) is the actual 32-bit memory address

 

 

 

 

 

 

 

 

 

 

used to perform the Load and Store to/from. When this

 

 

 

 

 

 

 

 

 

 

bit is set, the chip determines the memory address to

 

 

 

 

 

 

 

 

 

 

 

perform the Load and Store to/from by adding the 24-bit

 

 

 

 

 

 

 

 

 

 

signed offset value in the DMA SCRIPTS Pointer Save

 

 

 

 

 

 

 

 

 

 

 

(DSPS) to the Data Structure Address (DSA).

 

 

 

 

 

 

 

 

R

Reserved

 

 

[27:26]

 

 

 

 

 

 

NF

No Flush (Store instruction only)

25

 

 

 

 

 

 

 

 

 

 

When this bit is set, the LSI53C875A performs a Store

 

 

 

 

 

 

 

 

 

 

without flushing the prefetch unit. When this bit is cleared,

 

 

 

 

 

 

 

 

 

 

the Store instruction automatically flushes the prefetch

 

 

 

 

 

 

 

 

 

 

 

unit. Use No Flush if the source and destination are not

 

 

 

 

 

 

 

 

 

 

within four instructions of the current Store instruction.

 

 

 

 

 

 

 

 

 

 

 

This bit has no effect on the Load instruction.

 

 

5-36

SCSI SCRIPTS Instruction Set

Page 236
Image 236
LSI 53C875A technical manual IT20 Instruction Type 3129, DSA Relative, Reserved 2726 No Flush Store instruction only