Chapter 23.

Intel 80960 Dependent Features

23.1. i960 Command line Options

 ACA |  ACA_A |  ACB |  ACC |  AKA |  AKB |  AKC |  AMC

Select the 80960 architecture. Instructions or features not supported by the selected architecture

cause fatal errors.

 ACA

is equivalent to

 ACA_A

;

 AKC

is equivalent to

 AMC

. Synonyms are provided for compat 

ibility with other tools.

If you do not specify any of these options,

as

generates code for any instruction or feature that is

supported by some version of the 960 (even if this means mixing architectures!). In principle,

as

attempts to deduce the minimal sufficient processor type if none is specified; depending on the

object code format, the processor type may be recorded in the object file. If it is critical that the

as

output match a specific architecture, specify that architecture explicitly.

 b

Add code to collect information about conditional branches taken, for later optimization using

branch prediction bits. (The conditional branch instructions have branch prediction bits in the

CA, CB, and CC architectures.) If

BR

represents a conditional branch instruction, the following

represents the code generated by the assembler when

 b

is specified:

call

increment routine

.word

0

# pre counter

Label:

BR

call

increment routine

.word

0

# post counter

The counter following a branch records the number of times that branch was not taken; the

differenc between the two counters is the number of times the branch was taken.

A table of every such

Label

is also generated, so that the external postprocessor

gbr960

(sup 

plied by Intel) can locate all the counters. This table is always labeled

__BRANCH_TABLE__

; this

is a local symbol to permit collecting statistics for many separate object files. The table is word

aligned, and begins with a two word header. The first word, initialized to 0, is used in maintain 

ing linked lists of branch tables. The second word is a count of the number of entries in the table,

which follow immediately: each is a word, pointing to one of the labels illustrated above.

The first word of the header is used to locate multiple branch tables, since each object file may

contain one. Normally the links are maintained with a call to an initialization routine, placed at

the beginning of each function in the file. The gnu C compiler generates these calls automatically

when you give it a

 b

option. For further details, see the documentation of

gbr960

.

 no relax

Normally, Compare and Branch instructions with targets that require displacements greater than

13 bits (or that have external targets) are replaced with the corresponding compare (or

chkbit

)

and branch instructions. You can use the

 no relax

option to specify that

as

should generate

errors instead, if the target displacement is larger than 13 bits.