Revision 1.0
VU Loads and Stores
49
register of a VU load, hardware interlocking will stall the processor until the
data arrives.
Note:
VU stores use an identical pipeline; since accesses to memory
always occur in the same VU pipeline stage, a VU store followed by an
immediate load from the same memory location is guaranteed to fetch
the correct data.
VU stores followed by SU loads are also guaranteed to fetch the correct
data, for similar reasons.
VU loads and stores are of three types,
normal
,
packed
, and
transpose
.
Normal operations allow the movement of the usual integer memory data
items of powers of two numbers of bytes between memory and VU registers
with memory byte alignment, and VU element alignment to the size of the
item.
The packed operations support access to memory byte data and two and
four byte per pixel image data (such as
YUV
or
RGBA
).
Transpose accesses are discussed in a subsequent section, and include a
transposed or wrapped store, and a transposed and wrapped load.
Table 3-1
VU Load/Store Instruction Summary
Opcode
Memory Item
Memory
Alignment
VU Element
(legal values)
Offset Shift
Amount
lbv, sbv
8b (byte)
byte
0-15
<< 0
lsv, ssv
16b (short)
byte
0-14 by 2
<< 1
llv, slv
32b (long)
byte
0-12 by 4
<< 2
ldv, sdv
64b (double)
byte
0, 8
<< 3
lqv, sqv
128b (quad)
byte (see below)
0
<< 4
lrv, srv
128b (rest)
byte (see below)
0
<< 4
lpv, spv
8 8b, signed (pack)
byte (bit 15)
0
<< 3
luv, suv
8 8b, unsigned (upack)
byte (bit 14)
0
<< 3
lhv, shv
8 8b every 2nd,
unsigned (half pack)
quad+0,1
0
<< 4
N
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