IBM PPC440X5 Manual do Utilizador descarregar pdf (Página 73)

100

101

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]

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]

(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

agement

addo[.]

addco[.]

addeo[.]

addmeo[.]

addzeo[.]

subfo[.]

subfco[.]

subfeo[.]

subfmeo[.]

subfzeo[.]

mullwo[.]

divwo[.]

divwuo[.]

nego[.]

macchwo[.]

macchwso[.]

macchwsuo[.]

macchwuo[.]

machhwo[.]

machhwso[.]

machhwsuo[.]

machhwuo[.]

maclhwo[.]

maclhwso[.]

maclhwsuo[.]

maclhwuo[.]

nmacchwo[.]

nmacchwso[.]

nmachhwo[.]

nmachhwso[.]

nmaclhwo[.]

nmaclhwso[.]

mtspr

mcrxr

Table 2-26. XER[CA] Updating Instructions

Integer Arithmetic

Integer

Shift

Processor

Control

Add Subtract

Shift

Right

Algebraic

Management

addc[o][.]

adde[o][.]

addic[.]

addme[o][.]

addze[o][.]

subfc[o][.]

subfe[o][.]

subﬁc

subfme

[o][.]

subfze[o][.]

sraw[.]

srawi[.]

mtspr

mcrxr

1 2 ... 68 69 70 71 72 73 74 75 76 77 78 ... 589 590

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