Chapter 26. M680x0 Dependent Features

157

|

68020

68000/10, not PC relative OK

Pseudo Op |BYTE

WORD

LONG

ABSOLUTE LONG JUMP

**

+                                                            

jbsr |bsrs

bsrw

bsrl

jsr

jra |bras

braw

bral

jmp

*

jXX |bXXs

bXXw

bXXl

bNXs;jmp

*

dbXX | N/A

dbXXw

dbXX;bras;bral

dbXX;bras;jmp

fjXX | N/A

fbXXw

fbXXl

N/A

XX: condition

NX: negative of condition XX

*

  see full description below

**

  this expansion mode is disallowed by

 pcrel

jbsr

jra

These are the simplest jump pseudo operations; they always map to one particular machine in 

struction, depending on the displacement to the branch target. This instruction will be a byte or

word branch is that is sufficient. Otherwise, a long branch will be emitted if available. If no long

branches are available and the

 pcrel

option is not given, an absolute long jump will be emitted

instead. If no long branches are available, the

 pcrel

option is given, and a word branch cannot

reach the target, an error message is generated.

In addition to standard branch operands,

as

allows these pseudo operations to have all operands

that are allowed for jsr and jmp, substituting these instructions if the operand given is not valid

for a branch instruction.

jXX

Here,

jXX

stands for an entire family of pseudo operations, where

XX

is a conditional branch or

condition code test. The full list of pseudo ops in this family is:

jhi

jls

jcc

jcs

jne

jeq

jvc

jvs

jpl

jmi

jge

jlt

jgt

jle

Usually, each of these pseudo operations expands to a single branch instruction. However, if a

word branch is not sufficient, no long branches are available, and the

 pcrel

option is not given,

as

issues a longer code fragment in terms of

NX

, the opposite condition to

XX

. For example, under

these conditions:

jXX foo

gives

bNXs oof

jmp foo

oof:

dbXX

The full family of pseudo operations covered here is

dbhi

dbls

dbcc

dbcs

dbne

dbeq

dbvc

dbvs

dbpl

dbmi

dbge

dblt

dbgt

dble

dbf

dbra

dbt

Motorola

dbXX

instructions allow word displacements only. When a word displacement is suffi 

cient, each of these pseudo operations expands to the corresponding Motorola instruction. When

a word displacement is not sufficient and long branches are available, when the source reads

dbXX foo

,

as

emits

dbXX oo1

bras oo2

oo1:bral foo

oo2: