UM0438 datasheet(22/50 Pages) STMICROELECTRONICS

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Simplified mnemonics for VLE instructions

UM0438

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Appendix A

Simplified mnemonics for VLE instructions

This appendix describes simplified mnemonics for easier coding of assembly language

programs. Simplified mnemonics are defined for the most frequently used forms of branch

conditional, compare, trap, rotate and shift, and certain other instructions defined by the VLE

extension.

The simplified mnemonics for the VLE extension are similar to those defined for the

PowerPC programming environment. The result is a consistent programming view when

working with VLE instructions on PowerPC architectures. Section A.11: Comprehensive list

of simplified mnemonics provides an alphabetical listing of VLE simplified mnemonics used

by a variety of processors. Some assemblers may define additional simplified mnemonics

not included here. The simplified mnemonics listed here should be supported by all

compilers.

A.1

Overview

Simplified (or extended) mnemonics allow an assembly-language programmer to use more

intuitive mnemonics and symbols than the instructions and syntax defined by the instruction

set architecture. For example, to code the conditional call “branch to target if CR3 specifies

a greater than condition, setting the LR” without simplified mnemonics, the programmer

would write the branch conditional and link instruction e_bcl 1,13,target. The simplified

mnemonic, branch if greater than and link, e_bgtl cr3,target, incorporates the conditions.

Not only is it easier to remember the symbols than the numbers when programming, it is

also easier to interpret simplified mnemonics when reading existing code.

Simplified mnemonics are not a formal part of the architecture, but rather a recommendation

for assemblers that support the instruction set.

Simplified mnemonics for VLE instructions provide a consistent assembly-language

interface with the PowerPC architecture. Many simplified mnemonics were originally defined

in the PowerPC architecture documentation. Some assemblers created their own, and

others have been added to support extensions to the instruction set (for example, AltiVec

instructions and Book E auxiliary processing units (APUs)). Simplified mnemonics for new

architecturally defined and new implementation-specific special-purpose registers (SPRs)

are described here very generally.

A.2

Subtract simplified mnemonics

This section describes simplified mnemonics for subtract instructions.

A.2.1

Subtract immediate

The effect of a subtract immediate instruction can be achieved by negating the immediate

operand of the add immediate instructions, e_add16i, e_add2i., e_add2is, and e_addi.

Simplified mnemonics include this negation, making the intent of the computation clearer.

These are listed in Table 10.

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