“ARM inline Assembler”的版本间的差异

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第22行： 第22行：
 
cpsr = ps
 
cpsr = ps
  
 +
For ARM processors, GCC 4 provides the following constraints.
 +
{| class="wikitable" style="width:75%"
 +
! Constraint      !! Usage in ARM state          !! Usage in Thumb state
 +
|-
 +
|| f    || Floating point registers f0 .. f7    || Not available 
 +
|- 
 +
|| h|| Not available|| Registers r8..r15
 +
|-
 +
||G ||Immediate floating point constant ||Not available
 +
|-
 +
||H ||Same a G, but negated ||Not available
 +
|-
 +
||I ||Immediate value in data processing instructions e.g. ORR R0, R0, #operand ||Constant in the range 0 .. 255 e.g. SWI operand
 +
|-
 +
||J ||Indexing constants -4095 .. 4095 e.g. LDR R1, [PC, #operand] ||Constant in the range -255 .. -1 e.g. SUB R0, R0, #operand
 +
|-
 +
||K ||Same as I, but inverted ||Same as I, but shifted
 +
|-
 +
||L ||Same as I, but negated ||Constant in the range -7 .. 7 e.g. SUB R0, R1, #operand
 +
|-
 +
||l ||Same as r ||Registers r0..r7 e.g. PUSH operand 
 +
|-
 +
||M ||Constant in the range of 0 .. 32 or a power of 2 e.g. MOV R2, R1, ROR #operand  ||Constant that is a multiple of 4 in the range of 0 .. 1020 e.g. ADD R0, SP, #operand 
 +
|-
 +
||m ||Any valid memory address
 +
|-
 +
||N ||Not available ||Constant in the range of 0 .. 31 e.g. LSL R0, R1, #operand
 +
|-
 +
||O ||Not available ||Constant that is a multiple of 4 in the range of -508 .. 508 e.g. ADD SP, #operand
 +
|-
 +
||r ||General register r0 .. r15 e.g. SUB operand1, operand2, operand3 ||Not available
 +
|-
 +
||w ||Vector floating point registers s0 .. s31 ||Not available
 +
|-
 +
||X ||Any operand ||
 +
|}
  
 +
 +
Constraint characters may be prepended by a single constraint modifier. Constraints without a modifier specify read-only operands. Modifiers are:
 +
{| class="wikitable" style="width:75%"
 +
! Modifier      !! Specifies
 +
|-
 +
||=  ||Write-only operand, usually used for all output operands
 +
|-
 +
||+ ||Read-write operand, must be listed as an output operand
 +
|-
 +
||& ||A register that should be used for output only
 +
|}
 +
 +
Examples:
 +
* y=(y<<1);
 +
<source lang="c">
 +
asm("mov %[value], %[value], ror #1" : [value] "+r" (y));
 +
</source>
 +
use '+' for read-write able. Or,
 +
<source lang="c">
 +
asm("mov %0, %0, ror #1" : "=r" (value) : "0" (value));
 +
</source>
 +
Constraint "0" input reg = output reg
 +
 +
* rdv = table[0]; table[4]=wdr;
 +
<source lang="c">
 +
asm volatile("ldr %0, [%1]"    "\n\t"
 +
            "str %2, [%1, #4]" "\n\t"
 +
            : "=&r" (rdv) /* &  rdv 只能写  不可共用 
 +
            : "r" (&table), "r" (wdv)
 +
            : "memory");
 +
</source>
  
 
Referernce: http://www.ethernut.de/en/documents/arm-inline-asm.html
 
Referernce: http://www.ethernut.de/en/documents/arm-inline-asm.html

2019年11月8日 (五) 14:03的最后版本

asm(code : output operand list : input operand list : clobber list);

example: Rotating bits example
int x;
int y;
y= (x>>1); 

asm("mov %[result], %[value], ror #1" : [result] "=r" (y) : [value] "r" (x));

register value (r1) = x
register result (r2) = y
result = (value >> 1)

example: sets the current program status register of the ARM CPU. 

asm("msr cpsr,%[ps]" : : [ps]"r"(status));

int status;
ps (r2) = status
cpsr = ps

For ARM processors, GCC 4 provides the following constraints.

Constraint Usage in ARM state Usage in Thumb state
f Floating point registers f0 .. f7 Not available
h Not available Registers r8..r15
G Immediate floating point constant Not available
H Same a G, but negated Not available
I Immediate value in data processing instructions e.g. ORR R0, R0, #operand Constant in the range 0 .. 255 e.g. SWI operand
J Indexing constants -4095 .. 4095 e.g. LDR R1, [PC, #operand] Constant in the range -255 .. -1 e.g. SUB R0, R0, #operand
K Same as I, but inverted Same as I, but shifted
L Same as I, but negated Constant in the range -7 .. 7 e.g. SUB R0, R1, #operand
l Same as r Registers r0..r7 e.g. PUSH operand
M Constant in the range of 0 .. 32 or a power of 2 e.g. MOV R2, R1, ROR #operand Constant that is a multiple of 4 in the range of 0 .. 1020 e.g. ADD R0, SP, #operand
m Any valid memory address
N Not available Constant in the range of 0 .. 31 e.g. LSL R0, R1, #operand
O Not available Constant that is a multiple of 4 in the range of -508 .. 508 e.g. ADD SP, #operand
r General register r0 .. r15 e.g. SUB operand1, operand2, operand3 Not available
w Vector floating point registers s0 .. s31 Not available
X Any operand


Constraint characters may be prepended by a single constraint modifier. Constraints without a modifier specify read-only operands. Modifiers are:

Modifier Specifies
= Write-only operand, usually used for all output operands
+ Read-write operand, must be listed as an output operand
& A register that should be used for output only

Examples:

  • y=(y<<1); 
asm("mov %[value], %[value], ror #1" : [value] "+r" (y));

use '+' for read-write able. Or, 

asm("mov %0, %0, ror #1" : "=r" (value) : "0" (value));

Constraint "0" input reg = output reg

  • rdv = table[0]; table[4]=wdr; 
asm volatile("ldr %0, [%1]"     "\n\t"
             "str %2, [%1, #4]" "\n\t"
             : "=&r" (rdv) /* &  rdv 只能写  不可共用  
             : "r" (&table), "r" (wdv)
             : "memory");

Referernce: http://www.ethernut.de/en/documents/arm-inline-asm.html

来自“https://www.mywiki.cn/free6d1823/index.php?title=ARM_inline_Assembler&oldid=43791”