PM0215 datasheet(46/91 Pages) STMICROELECTRONICS

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The STM32 Cortex-M0 instruction set

PM0215

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Doc ID 022979 Rev 1

3.4.5

LDM and STM

Load and store multiple registers.

Syntax

LDM Rn{!}, reglist

STM Rn!, reglist

where:

●

‘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

LDMIA and LDMFD are synonyms for LDM. LDMIA refers to the base register being

Incremented After each access. LDMFD refers to its use for popping data from Full

Descending stacks.

STMIA and STMEA are synonyms for STM. STMIA refers to the base register being

Incremented After each access. STMEA refers to its use for pushing data onto Empty

Ascending stacks.

Operation

LDM loads the registers in reglist with word values from memory addresses based on Rn.

STM stores the word values in the registers in reglist to memory addresses based on Rn.

The memory addresses used for 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 register using the highest memory address. If the

writeback suffix is specified, the value in the register specified by of Rn + 4 * (n) or is written

back to the register specified by Rn.

Restrictions

In these instructions:

●

reglist and Rn are limited to R0-R7.

●

the writeback suffix must always be used unless the instruction is an LDM where reglist

also contains Rn, in which case the writeback suffix must not be used.

●

the value in the register specified by Rn must be word aligned. See Address alignment

on page 39 for more information.

●

for STM, if Rn appears in reglist, then it must be the first register in the list.

Condition flags

These instructions do not change the flags.

Examples

LDM

R0,{R0,R3,R4}

; LDMIA is a synonym for LDM

STMIA R1!,{R2-R4,R6}

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