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Overview of the Assembler Overview of the ARM Architecture Structure of Assembly Language Modules 
Writing ARM Assembly Language Unified Assembler Language Subroutines calls Load immediates into registers Load immediate values using MOV and MVN Load 32-bit values to a register using MOV32 Load immediate 32-bit values to a register using L Literal pools Load addresses into registers Load addresses to a register using ADR Load addresses to a register using ADRL Load addresses to a register using LDR Rd, =label Other ways to Load and store registers Load and store multiple register instructions Load and store multiple instructions available in Stack implementation using LDM and STM Stack operations for nested subroutines Block copy with LDM and STM Memory accesses Read-Modify-Write procedure Optional hash Use of macros Test-and-branch macro example Unsigned integer division macro example Instruction and directive relocations Symbol versions Frame directives Exception tables and Unwind tables Assembly language changes after RVCTv2.1 Condition Codes Using the Assembler Symbols, Literals, Expressions, and Operators VFP ProgrammingStack implementation using LDM and STM
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The load and store multiple instructions can update the base register. For stack operations, the base register is usually the stack pointer, SP. This means that you can use these instructions to implement push and pop operations for any number of registers in a single instruction.
The load and store multiple instructions can be used with several types of stack:
- Descending or ascending
The stack grows downwards, starting with a high address and progressing to a lower one (a descending stack), or upwards, starting from a low address and progressing to a higher address (an ascending stack).
- Full or empty
The stack pointer can either point to the last item in the stack (a full stack), or the next free space on the stack (an empty stack).
To make it easier for the programmer, stack-oriented suffixes can be used instead of the increment or decrement, and before or after suffixes. Table 10 shows the stack-oriented suffixes and their equivalent addressing mode suffixes for load and store instructions.
Table 10. Stack-oriented suffixes and equivalent addressing mode suffixes
| Stack-oriented suffix | For store or push instructions | For load or pop instructions |
|---|---|---|
| FD (Full Descending stack) | DB (Decrement Before) | IA (Increment After) |
| FA (Full Ascending stack) | IB (Increment Before) | DA (Decrement After) |
| ED (Empty Descending stack) | DA (Decrement After) | IB (Increment Before) |
| EA (Empty Ascending stack) | IA (Increment After) | DB (Decrement Before) |
Table 11 shows the load and store multiple instructions with the stack-oriented suffixes for the various stack types.
Table 11. Suffixes for load and store multiple instructions
| Stack type | Store | Load |
|---|---|---|
| Full descending | STMFD (STMDB, Decrement Before) | LDMFD (LDM, increment after) |
| Full ascending | STMFA (STMIB, Increment Before) | LDMFA (LDMDA, Decrement After) |
| Empty descending | STMED (STMDA, Decrement After) | LDMED (LDMIB, Increment Before) |
| Empty ascending | STMEA (STM, increment after) | LDMEA (LDMDB, Decrement Before) |
For example:
STMFD sp!, {r0-r5} ; Push onto a Full Descending Stack
LDMFD sp!, {r0-r5} ; Pop from a Full Descending Stack
Note
The Procedure Call Standard for the ARM Architecture (AAPCS), and ARM and Thumb C and C++ compilers always use a full descending stack.
The PUSH and POP instructions assume a full descending stack. They are the preferred synonyms for STMDB and LDM with writeback.
See also| Copyright © 2007-2008, 2011 ARM. All rights reserved. | ARM DUI 0379C |
| Non-Confidential | ID061811 |
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