Chapter 16.

D30V Dependent Features

16.1. D30V Options

The Mitsubishi D30V version of

as

has a few machine dependent options.

 O

The D30V can often execute two sub instructions in parallel. When this option is used,

as

will

attempt to optimize its output by detecting when instructions can be executed in parallel.

 n

When this option is used,

as

will issue a warning every time it adds a nop instruction.

 N

When this option is used,

as

will issue a warning if it needs to insert a nop after a 32 bit multiply

before a load or 16 bit multiply instruction.

16.2. Syntax

The D30V syntax is based on the syntax in Mitsubishi's D30V architecture manual. The differences

are detailed below.

16.2.1. Size Modifiers

The D30V version of

as

uses the instruction names in the D30V Architecture Manual. However, the

names in the manual are sometimes ambiguous. There are instruction names that can assemble to

a short or long form opcode. How does the assembler pick the correct form?

as

will always pick

the smallest form if it can. When dealing with a symbol that is not defined yet when a line is being

assembled, it will always use the long form. If you need to force the assembler to use either the short

or long form of the instruction, you can append either

.s

(short) or

.l

(long) to it. For example, if you

are writing an assembly program and you want to do a branch to a symbol that is defined later in your

program, you can write

bra.s foo

. Objdump and GDB will always append

.s

or

.l

to instructions

which have both short and long forms.

16.2.2. Sub Instructions

The D30V assembler takes as input a series of instructions, either one per line, or in the special two 

per line format described in the next section. Some of these instructions will be short form or sub 

instructions. These sub instructions can be packed into a single instruction. The assembler will do this

automatically. It will also detect when it should not pack instructions. For example, when a label is

defined, the next instruction will never be packaged with the previous one. Whenever a branch and

link instruction is called, it will not be packaged with the next instruction so the return address will be

valid. Nops are automatically inserted when necessary.

If you do not want the assembler automatically making these decisions, you can control the packaging

and execution type (parallel or sequential) with the special execution symbols described in the next

section.