User’s Manual
Preliminary
PPC440x5 CPU Core
prgmodel.fm.
September 12, 2002
Page 73 of 589
2.6.2.1 Summary Overflow (SO) Field
This field is set to 1 when an instruction is executed that causes XER[OV] to be set to 1, except for the case
of
mtspr(XER), which writes XER[SO,OV] with the values in (RS)
0:1
, respectively. Once set, XER[SO] is not
reset until either an
mtspr(XER) is executed with data that explicitly writes 0 to XER[SO], or until an mcrxr
instruction is executed. The mcrxr instruction sets XER[SO] (as well as XER[OV,CA]) to 0 after copying all
three fields into CR[CR0]
0:2
(and setting CR[CR0]
3
to 0).
Given this behavior, XER[SO] does not necessarily indicate that an overflow occurred on the most recent
integer arithmetic operation, but rather that one occurred at some time subsequent to the last clearing of
XER[SO] by mtspr(XER) or mcrxr.
XER[SO] is read (along with the rest of the XER) into a GPR by mfspr(XER). In addition, various integer
instructions copy XER[SO] into CR[CR0]
3
(see Condition Register (CR) on page 67).
Table 2-25. XER[SO,OV] Updating Instructions
Integer Arithmetic
Auxiliary Processor
Processor Con-
trol
Add
Subtract
Multiply
Divide
Negate
Multiply-Accumu-
late
Negative Multi-
ply- Accumulate
Register Man-
agement
addo
[
.
]
addco
[
.
]
addeo
[
.
]
addmeo
[
.
]
addzeo
[
.
]
subfo
[
.
]
subfco
[
.
]
subfeo
[
.
]
subfmeo
[
.
]
subfzeo
[
.
]
mullwo
[
.
]
divwo
[
.
]
divwuo
[
.
]
nego
[
.
]
macchwo
[
.
]
macchws
o[
.
]
macchwsu
o[
.
]
macchwu
o[
.
]
machhw
o[
.
]
machhws
o[
.
]
machhwsu
o[
.
]
machhwu
o[
.
]
maclhw
o[
.
]
maclhws
o[
.
]
maclhwsu
o[
.
]
maclhwu
o[
.
]
nmacchw
o[
.
]
nmacchws
o[
.
]
nmachhw
o[
.
]
nmachhws
o[
.
]
nmaclhw
o[
.
]
nmaclhws
o[
.
]
mtspr
mcrxr
Table 2-26. XER[CA] Updating Instructions
Integer Arithmetic
Integer
Shift
Processor
Control
Add
Subtract
Shift
Right
Algebraic
Register
Management
addc
[
o
][
.
]
adde
[
o
][
.
]
addic
[
.
]
addme
[
o
][
.
]
addze
[
o
][
.
]
subfc
[
o
][
.
]
subfe
[
o
][
.
]
subfic
subfme
[
o
][
.
]
subfze
[
o
][
.
]
sraw
[
.
]
srawi
[
.
]
mtspr
mcrxr
Содержание PPC440X5 CPU Core
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