Arm VERSION 1.2 Manual do Utilizador descarregar pdf (Página 72)

100

101

Writing ARM and Thumb Assembly Language

Making faster access possible

To gain faster access to a section of memory:

1. Describe the memory section as a structure.

2. Use a register to address the structure.

For example, consider the definitions in Example 2-22.

Example 2-22

StartOfData EQU 0x1000

EndOfData EQU 0x2000

MAP StartOfData

Integer FIELD 4

String FIELD MaxStrLen

Array FIELD ArrayLen*8

BitMask FIELD 4

EndOfUsedData FIELD 0

ASSERT EndOfUsedData <= EndOfData

If you want the equivalent of the C code:

Integer = 1;

String = "";

BitMask = 0xA000000A;

With the definitions from Example 2-22, the assembly language code can be as shown

in Example 2-23.

Example 2-23

MOV r0,#1

LDR r1,=Integer

STR r0,[r1]

MOV r0,#0

LDR r1,=String

STRB r0,[r1]

MOV r0,#0xA000000A

LDR r1,=BitMask

STRB r0,[r1]

Example 2-23 uses

LDR

pseudo-instructions. Refer to Loading with LDR Rd, =const on

page 2-27 for an explanation of these.

1 2 ... 67 68 69 70 71 72 73 74 75 76 77 ... 359 360

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