36
RSP Architecture
Accumulator
Each vector slice has a 48-bit accumulator associated with it. Each 16-bit
element of a vector register maps to a vector slice, and therefore to a different
48-bit accumulator.
Figure 2-4
VU Accumulator Format
The accumulator is modified by most VU computational instructions, but it
is used most heavily by the multiply-accumulate instructions. For these
instructions, 16-bits of the accumulator is written out after accumulation.
“Which” 16-bits to be written is usually an accumulator element. Consult
“VU Multiply Instructions” in Chapter 3 for more information.
One VU instruction,
vsar
, can directly reference the accumulator directly.
VU Control Registers
Vector Compare Code Register (VCC)
This 16-bit register contains 2 bits per 16-bit slice of the VU and is used by
the select instructions.
47
0
byte 2
byte 3
byte 4
byte 5
byte 0
byte 1
high
low
middle
Summary of Contents for Ultra64
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