Cypress DCT-1D Betriebsanweisung PDF herunterladen (Seite 66)

CHAPTER 6. LAB TASK 4 - CUSTOM INSTRUCTIONS

: o u t p u t o p e r a n d s

: i n p u t o p e r a n d s

: l i s t o f c l o b b e r e d r e g i s t e r s

) ;

The

asm volatile

keyword instructs the compiler to insert exactly this assembler in-

struction at exactly this position into the compiled code.

The ﬁrst part of the construct is an assembler template string, e.g.

"l.sd 0x0(%0),%1"

The output operands is a comma separated list of output operands, the one you

most probably are going to use is

"=r"(var)

meaning that the output from the assembly

instruction is a write only to a register operation and that the the variable

var

in the C

code is assigned the output value.

The input operand list is a comma separated list of input operands. The format you

most probably are going to use is the

"r"(var_in)

. This means that the variable

var_in

is assigned to a register used in the assembly instruction.

The input and output operands are mapped, by order of appearance, to the

"assem-

bler template"

string. E.g.

"l.or %0,%1,%2" : "=r"(res) : "r"(in_a), "r"(in_b)

will

map the

res

to be the destination (%0),

in_a

source one (%1), and

in_b

source two

(%2).

The list of clobbered registers is a comma separated list of registers that have been

modiﬁed by the assembly and not assigned by the compiler with the

notation. I.e.

if you have written

asm volatile("l.ori r20,r10,r11") r20

has to be listed as a clobbered

asm volatile("l.ori r20,r10,r11"::"r20")

. This since the compiler must

be informed if we modify some registers in the inline assembly instruction, otherwise

it will happily assume that the value of a register is the same after the inline assembly

block as it was before the s ection in question.

If you want to write a consecutive block of assembler code this is done as shown

in Listing 6.2.

Listing 6.2: Consecutive block of inline assembler.

asm v o l a t i l e ( "l.instr ␣%0 ,␣%2,␣%3" "\n\t"

"l.bnf␣label_1" "\n\t"

"l.nop␣0x0" "\n\t"

"l.movhi ␣%1,␣%4" "\n\t"

"l.j␣ label_2" "\n\t"

"l.nop␣0x0" "\n\t"

"label_1 :" "\n\t"

"l.movhi ␣%1,␣%5" "\n\t"

"label_2 :" "\n\t"

: "=r" ( r e s 1 ) , "=r" ( r e s 2 )

: "r" ( ar g 1 ) , "r" ( a r g 2 ) , "i" ( 0 x1 ) , "i" ( 0 x0 ) ) ;

To omit the

is not a syntactic error, but if not used the disassembled object

ﬁle will look messed up. We can also see from Listing 6.2 that it is poss ible to use

labels in inline assembler constructs.

For a more detailed description of the gcc in-line assembly see [15]

1 2 ... 61 62 63 64 65 66 67 68 69 70 71 ... 81 82

Kommentare zu diesen Handbüchern

Keine Kommentare

Cypress DCT-1D Betriebsanweisung Seite 66

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Nein Cypress DCT-1D