PM0056 datasheet(67/156 Pages) STMICROELECTRONICS

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PM0056

The Cortex-M3 instruction set

3.4.6

LDM and STM

Load and store multiple registers.

Syntax

op{addr_mode}{cond} Rn{!}, reglist

where:

•

‘op’ is either LDM (load multiple register) or STM (store multiple register)

•

‘addr_mode’ is any of the following:

IA: Increment address after each access (this is the default)

DB: Decrement address before each access

•

‘cond’ is an optional condition code (see Conditional execution on page 57)

•

‘Rn’ is the register on which the memory addresses are based

•

‘!’ is an optional writeback suffix. If ‘!’ is present, the final address that is loaded from or

stored to is written back into Rn.

•

‘reglist’ is a list of one or more registers to be loaded or stored, enclosed in braces. It

can contain register ranges. It must be comma-separated if it contains more than one

LDM and LDMFD are synonyms for LDMIA. LDMFD refers to its use for popping data from

full descending stacks.

LDMEA is a synonym for LDMDB, and refers to its use for popping data from empty

ascending stacks.

STM and STMEA are synonyms for STMIA. STMEA refers to its use for pushing data onto

empty ascending stacks.

STMFD is s synonym for STMDB, and refers to its use for pushing data onto full descending

stacks

Operation

LDM instructions load the registers in reglist with word values from memory addresses

based on Rn.

STM instructions store the word values in the registers in reglist to memory addresses based

on Rn.

For LDM, LDMIA, LDMFD, STM, STMIA, and STMEA the memory addresses used for the

accesses are at 4-byte intervals ranging from Rn to Rn + 4 * (n-1), where n is the number of

registers in reglist. The accesses happen in order of increasing register numbers, with the

lowest numbered register using the lowest memory address and the highest number

Rn + 4 * (n-1) is written back to Rn.

For LDMDB, LDMEA, STMDB, and STMFD the memory addresses used for the accesses

are at 4-byte intervals ranging from Rn to Rn - 4 * (n-1), where n is the number of registers in

reglist. The accesses happen in order of decreasing register numbers, with the highest

numbered register using the highest memory address and the lowest number register using

the lowest memory address. If the writeback suffix is specified, the value Rn - 4 * (n-1) is

written back to Rn.

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