UM0438 datasheet(29/50 Pages) STMICROELECTRONICS

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UM0438

Simplified mnemonics for VLE instructions

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Specifying a CR Bit

Note that the AIM version of the PowerPC architecture numbers CR bits 0–31 and Book E

numbers them 32–63. However, no adjustment is necessary to the code; in Book E devices,

32 is automatically added to the BI32 and BI16 values, as shown in Table 15 and Table 16.

Some simplified mnemonics incorporate only the BO32 or BO16 fields (as described

Section A.4.2: Eliminating the BO32 and BO16 operands). If one of these simplified

mnemonics is used and the CR must be accessed, the BI32 or BI16 operand can be

specified either as a numeric value or by using the symbols in Table 16.

Compare word instructions (described in Section A.6: Compare word simplified

mnemonics), floating-point compare instructions, move to CR instructions, and others can

also modify CR fields, so CR0 and CR1 may hold values that do not adhere to the meanings

described in Table 15.

Table 15.

CR0 and CR1 fields as updated by integer and floating-point instructions

CRn Bit

CR Bits

BI32

BI16

Description

AIM Book E

0–1

2–3

0–1

CR0[0]

Negative (LT)—Set when the result is negative.

CR0[1]

Positive (GT)—Set when the result is positive (and not zero).

CR0[2]

Zero (EQ)—Set when the result is zero.

CR0[3]

Summary overflow (SO). Copy of XER[SO] at the instruction’s

completion.

CR1[0]

—

Copy of FPSCR[FX] at the instruction’s completion.

CR1[1]

—

Copy of FPSCR[FEX] at the instruction’s completion.

CR1[2]

—

Copy of FPSCR[VX] at the instruction’s completion.

CR1[3]

—

Copy of FPSCR[OX] at the instruction’s completion.

Table 16.

BI32 and BI16 operand settings for CR fields for branch comparisons

crn

bit

bit expression

CR bits

bi32

bi16

Description

AIM BI

operand

Book E 0–1 2–3

0–1

crn[0]

4 * cr0 + lt (or lt)

4 * cr1 + lt

4 * cr2 + lt

4 * cr3+ lt

—

less than or floating-point less than (lt, fl).

for integer compare instructions:

ra < simm or rb (signed comparison) or ra <

uimm or rb (unsigned comparison).

for floating-point compare instructions: fra <

frb.

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