Avago Technologies LSI8751D - Manual (Page 233)

Load and Store Instructions 6-37
6.7 Load and Store Instructions
The Load and Store instructions provide a more efficient way to move
data from/to memory to/from an internal register in the chip without using
the normal memory move instruction.
The Load and Store instructions are represented by two Dword opcodes.
The first Dword contains the
DMA Command (DCMD) and DMA Byte
Counter (DBC) register values. The second Dword contains the DMA
SCRIPTS Pointer Save (DSPS) value. This is either the actual memory
location of where to Load or Store, or the offset from the Data Structure
Address (DSA) , depending on the value of bit 28 (DSA Relative).
A maximum of 4 bytes may be moved with these instructions. The
register address and memory address must have the same byte
alignment, and the count set such that it does not cross Dword
boundaries. The destination memory address in the Store instruction and
the source memory address of the Load instruction may not map back
to the operating register set of the chip. This excludes the SCRIPTS
RAM and ROM memory spaces. If it does, a PCI read/write cycle occurs
(the data does not actually transfer to/from the chip), and the chip issues
an interrupt (Illegal Instruction Detected) immediately following.
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 A1 Bit A0 Number of Bytes Allowed to Load and Store
0 0 One, two, three or four
0 1 One, two, or three
1 0 One or two
1 1 One