ldm

Load Multiple (Thumb)

LDM <Rn>!, <registers>

Load multiple registers (Thumb 16-bit).

Pseudocode Operation

address ← Rn
for each register in register_list (in ascending order):
  register ← [address]
  address ← address + 4
Rn ← address
if PC in register_list:
  PC ← loaded_PC_value

Example

LDM r1!, registers

Encoding

Binary Layout

1100

15:12

1

11

Rn

10:8

register_list

7:0

 

Format Thumb Load Multiple

Opcode 0xC800

Extension T32 (Base)

Operands

• Rn
  First source / base general-purpose register
• registers
  List

Related

Other forms of ldm

• ldm Load Multiple (A32)

More in T32 (Base)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x08900000	LDM{IA}{<c>}{<q>} <Rn>{!}, <registers>		A32		cond | 100 | 0 | 1 | 0 | W | 1 | Rn | register_list
0xC800	LDM{IA}{<c>}{<q>} <Rn>{!}, <registers>		T32		1100 | 1 | Rn | register_list
0xE8900000	LDM{IA}{<c>}.W <Rn>{!}, <registers>		T32		1110100 | 01 | 0 | W | 1 | Rn | P | M | register_list
0x08508000	LDM{<amode>}{<c>}{<q>} <Rn>{!}, <registers_with_pc>^		A32		cond | 100 | P | U | 1 | W | 1 | Rn | 1 | register_list
0x08500000	LDM{<amode>}{<c>}{<q>} <Rn>, <registers_without_pc>^		A32		cond | 100 | P | U | 1 | 0 | 1 | Rn | 0 | register_list
0x08100000	LDMDA{<c>}{<q>} <Rn>{!}, <registers>		A32		cond | 100 | 0 | 0 | 0 | W | 1 | Rn | register_list
0x09100000	LDMDB{<c>}{<q>} <Rn>{!}, <registers>		A32		cond | 100 | 1 | 0 | 0 | W | 1 | Rn | register_list
0xE9100000	LDMDB{<c>}{<q>} <Rn>{!}, <registers>		T32		1110100 | 10 | 0 | W | 1 | Rn | P | M | register_list
0x09900000	LDMIB{<c>}{<q>} <Rn>{!}, <registers>		A32		cond | 100 | 1 | 1 | 0 | W | 1 | Rn | register_list

Description

Load Multiple (Increment After, Full Descending) loads multiple registers from consecutive memory locations using an address from a base register. The consecutive memory locations start at this address, and the address just above the highest of those locations can optionally be written back to the base register. The lowest-numbered register is loaded from the lowest memory address, through to the highest-numbered register from the highest memory address. See also Encoding of lists of general-purpose registers and the PC. Armv8.2 permits the deprecation of some Load Multiple ordering behaviors in AArch32 state, for more information see FEAT_LSMAOC. The registers loaded can include the PC, causing a branch to a loaded address. This is an interworking branch, see Pseudocode description of operations on the AArch32 general-purpose registers and the PC. Related system instructions are LDM (User registers) and LDM (exception return).

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    address = R[n];
    for i = 0 to 14
        if registers<i> == '1' then
            R[i] = MemS[address,4];  address = address + 4;
    if registers<15> == '1' then
        LoadWritePC(MemS[address,4]);
    if wback && registers<n> == '0' then R[n] = R[n] + 4*BitCount(registers);
    if wback && registers<n> == '1' then R[n] = bits(32) UNKNOWN;