PM0214 datasheet(78/245 Pages) STMICROELECTRONICS

78 / 245 page

The STM32 Cortex-M4 instruction set

PM0214

78/245

DocID022708 Rev 4

3.4.8

LDREX and STREX

Load and store register exclusive.

Syntax

LDREX{cond} Rt, [Rn {, #offset}]

STREX{cond} Rd, Rt, [Rn {, #offset}]

LDREXB{cond} Rt, [Rn]

STREXB{cond} Rd, Rt, [Rn]

LDREXH{cond} Rt, [Rn]

STREXH{cond} Rd, Rt, [Rn]

where:

•

‘cond’ is an optional condition code (see Conditional execution on page 64)

•

‘Rd’ is the destination register for the returned status

•

‘Rt’ is the register to load or store

•

‘Rn’ is the register on which the memory address is based

•

‘offset’ is an optional offset applied to the value in Rn. If offset is omitted, the address is

the value in Rn.

Operation

LDREX, LDREXB, and LDREXH load a word, byte, and halfword respectively from a

memory address.

STREX, STREXB, and STREXH attempt to store a word, byte, and halfword respectively to

a memory address. The address used in any store-exclusive instruction must be the same

as the address in the most recently executed load-exclusive instruction. The value stored by

the store-exclusive instruction must also have the same data size as the value loaded by the

preceding load-exclusive instruction. This means software must always use a load-

exclusive instruction and a matching store-exclusive instruction to perform a

synchronization operation, see Synchronization primitives on page 33.

If a store-exclusive instruction performs the store, it writes 0 to its destination register.

If it does not perform the store, it writes 1 to its destination register.

If the store-exclusive instruction writes 0 to the destination register, it is guaranteed that no

other process in the system has accessed the memory location between the load-exclusive

and store-exclusive instructions.

For reasons of performance, keep the number of instructions between corresponding load-

exclusive and store-exclusive instruction to a minimum.

Note:

The result of executing a store-exclusive instruction to an address that is different from that

used in the preceding load-exclusive instruction is unpredictable.

PM0214 Datasheet(PDF) 78 Page - STMicroelectronics

PM0214 Datasheet(HTML) 78 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL