ARM VERSION 1.2 manual This example, the MAP directive is, Not

Writing ARM and Thumb Assembly Language

Example 2-23 on page 2-60 contains separate LDR pseudo-instructions to load the address of each of the data items. Each LDR pseudo-instruction is converted to a separate instruction by the assembler. However, it is possible to access the entire data section with a single LDR pseudo-instruction. Example 2-24 shows how to do this. Both speed and code size are improved.

Example 2-24

	AREA	data, DATA
StartOfData	EQU	0x1000
EndOfData	EQU	0x2000
DataAreaBase	RN	r11
	MAP	0,DataAreaBase
StartOfUsedData	FIELD	0
Integer	FIELD	4
String	FIELD	MaxStrLen
Array	FIELD	ArrayLen*8
BitMask	FIELD	4
EndOfUsedData	FIELD	0
UsedDataLen	EQU	EndOfUsedData - StartOfUsedData
	ASSERT	UsedDataLen <= (EndOfData - StartOfData)
	AREA	code, CODE
	LDR	DataAreaBase,=StartOfData
	MOV	r0,#1
	STR	r0,Integer
	MOV	r0,#0
	STRB	r0,String
	MOV	r0,#0xA000000A
	STRB	r0,BitMask

Note

In this example, the MAP directive is:

MAP 0, DataAreaBase

not:

MAP StartOfData,DataAreaBase

The MAP and FIELD directives give the position of the data relative to the DataAreaBase register, not the absolute position. The LDR DataAreaBase,=StartOfData statement provides the absolute position of the entire data section.

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