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Preface Introduction Writing ARM Assembly Language
Introduction Overview of the ARM architecture Architecture versions ARM, Thumb, Thumb‑2, and Thumb‑2EE instruction ARM, Thumb, and ThumbEE state Processor mode Registers Instruction set overview Instruction capabilities Structure of assembly language modules Layout of assembly language source files An example ARM assembly language module Calling subroutines Conditional execution The ALU status flags Conditional execution Using conditional execution Example of the use of conditional execution The Q flag Loading constants into registers Direct loading with MOV and MVN Loading with MOV32 Loading with LDR Rd, =const Loading addresses into registers Direct loading with ADR and ADRL Loading addresses with LDR Rd, =label Load and store multiple register instructions Load and store multiple instructions available in Implementing stacks with LDM and STM Block copy with LDM and STM Using macros Test‑and‑branch macro example Unsigned integer division macro example Using frame directives Assembly language changes Assembler Reference ARM and Thumb Instructions Directives ReferenceDirect loading with MOV and MVN
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| Home > Writing ARM Assembly Language > Loading constants into registers > Direct loading with MOV and MVN | |||
In ARM and Thumb‑2, you can use the 32‑bit MOV and MVN instructions to load a wide range of constant values directly into a register.
The 16‑bit Thumb MOV instruction can load any constant in the range 0‑255. You cannot use the 16‑bit MVN instruction to load a constant.
ARM state immediate constants shows the range of values that can be loaded in a single instruction in ARM. Thumb‑2 immediate constants shows the range of values that can be loaded in a single instruction in Thumb‑2.
You do not have to decide whether to use MOV or MVN. The assembler uses whichever is appropriate. This is useful if the value is an assembly-time variable.
If you write an instruction with a constant that is not available, the assembler reports the error: Immediate n out of range for this operation.
In ARM state:
MOVcan load any 8‑bit constant value, giving a range of0x0‑0xFF(0‑255).It can also rotate these values by any even number.
These values are also available as immediate operands in many data processing operations, without being loaded in a separate instruction.
MVNcan load the bitwise complements of these values. The numerical values are‑(, wheren+1)nMOV.In ARMv6T2 and above,
MOVcan load any 16‑bit number, giving a range of0x0‑0xFFFF(0‑65535).
Table 2.5 shows the range of 8‑bit values that this provides (for data processing operations).
Table 2.6 shows the range of 16‑bit values that this provides (for MOV instructions only).
Table 2.5. ARM state immediate constants (8‑bit)
| Binary | Decimal | Step | Hexadecimal | MVN valuea | Notes |
|---|---|---|---|---|---|
000000000000000000000000abcdefgh | 0‑255 | 1 | 0‑0xFF | –1 to –256 | ‑ |
0000000000000000000000abcdefgh00 | 0‑1020 | 4 | 0‑0x3FC | –4 to –1024 | ‑ |
00000000000000000000abcdefgh0000 | 0‑4080 | 16 | 0‑0xFF0 | –16 to –4096 | ‑ |
000000000000000000abcdefgh000000 | 0‑16320 | 64 | 0‑0x3FC0 | –64 to –16384 | ‑ |
| ... | ... | ... | ... | ‑ | |
abcdefgh000000000000000000000000 | 0‑255 x 224 | 224 | 0‑0xFF000000 | 1‑256 x –224 | ‑ |
cdefgh000000000000000000000000ab | (bit pattern) | ‑ | ‑ | (bit pattern) | See b in Notes |
efgh000000000000000000000000abcd | (bit pattern) | ‑ | ‑ | (bit pattern) | See b in Notes |
gh000000000000000000000000abcdef | (bit pattern) | ‑ | ‑ | (bit pattern) | See b in Notes |
Table 2.6. ARM state immediate constants in MOV instructions
| Binary | Decimal | Step | Hexadecimal | MVN value | Notes |
|---|---|---|---|---|---|
0000000000000000abcdefghijklmnop | 0‑65535 | 1 | 0‑0xFFFF | ‑ | See c in Notes |
These notes give extra information on Table 2.5 and Table 2.6.
- a
The
MVNvalues are not available directly as operands in other, non data processing, instructions.- b
These values are available in ARM state only. All the other values in this table are also available in Thumb‑2, except where noted.
- c
These values are only available in ARMv6T2 and above. They are not available directly as operands in other instructions.
In Thumb state, in ARMv6T2 and above:
the 32‑bit
MOVinstruction can load:any 8‑bit constant value, giving a range of
0x0‑0xFF(0‑255)any 8‑bit constant value, shifted left by any number
any 8‑bit bit pattern duplicated in all four bytes of a register
any 8‑bit bit pattern duplicated in bytes 0 and 2, with bytes 1 and 3 set to 0
any 8‑bit bit pattern duplicated in bytes 1 and 3, with bytes 0 and 2 set to 0.
These values are also available as immediate operands in many data processing operations, without being loaded in a separate instruction.
the 32‑bit
MVNinstruction can load the bitwise complements of these values. The numerical values are‑(, wheren+1)nMOV.the 32‑bit
MOVinstruction can load any 16‑bit number, giving a range of0x0‑0xFFFF(0‑65535). These values are not available as immediate operands in data processing operations.
Table 2.7 shows the range of values that this provides (for data processing operations).
Table 2.8 shows the range of 16‑bit values that this provides (for MOV instructions only).
Table 2.7. Thumb state immediate constants
| Binary | Decimal | Step | Hexadecimal | MVN valuea | Notes |
|---|---|---|---|---|---|
000000000000000000000000abcdefgh | 0‑255 | 1 | 0‑0xFF | –1 to –256 | ‑ |
00000000000000000000000abcdefgh0 | 0‑510 | 2 | 0‑0x1FE | –2 to –512 | ‑ |
0000000000000000000000abcdefgh00 | 0‑1020 | 4 | 0‑0x3FC | –4 to –1024 | ‑ |
| ... | ... | ... | ... | ‑ | |
0abcdefgh00000000000000000000000 | 0‑255 x 223 | 223 | 0‑0x7F800000 | 1‑256 x –223 | ‑ |
abcdefgh000000000000000000000000 | 0‑255 x 224 | 224 | 0‑0xFF000000 | 1‑256 x –224 | ‑ |
abcdefghabcdefghabcdefghabcdefgh | (bit pattern) | ‑ | 0xXYXYXYXY | 0xXYXYXYXY | ‑ |
00000000abcdefgh00000000abcdefgh | (bit pattern) | ‑ | 0x00XY00XY | 0xFFXYFFXY | ‑ |
abcdefgh00000000abcdefgh00000000 | (bit pattern) | ‑ | 0xXY00XY00 | 0xXYFFXYFF | ‑ |
00000000000000000000abcdefghijkl | 0‑4095 | 1 | 0‑0xFFF | ‑ | See b in Notes |
Table 2.8. Thumb state immediate constants in MOV instructions
| Binary | Decimal | Step | Hexadecimal | MVN value | Notes |
|---|---|---|---|---|---|
0000000000000000abcdefghijklmnop | 0‑65535 | 1 | 0‑0xFFFF | ‑ | See c in Notes |
These notes give extra information on Table 2.7 and Table 2.8.
- a
The
MVNvalues are not available directly as operands in other instructions.- b
These values are available directly as operands in
ADD,SUB, andMOVinstructions, but not inMVNor any other data processing instructions.- c
These values are only available in
MOVinstructions.
| Copyright © 2007 ARM Limited. All rights reserved. | ARM DUI 0379A |
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