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5-36 SCSI SCRIPTS Instruction Set
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.
5.8.1 First Dword
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.
Bit Source Destination
SIOM (Load) Memory Register
DIOM (Store) Register Memory
31 29 28 27 26 25 24 23 22 16 15 3 2 0
DMA Command (DCMD)
Register
DMA Byte Counter (DBC) Register
IT[2:0] DSA
RNFLSR RA[6:0] RBC
111 x
0 0xx0xxxxxxx0 0 0 0 0 0 0 0 0 0 0 0 0xxx