SAM3N0C Atmel Corporation, SAM3N0C Datasheet - Page 58

• Manufacturer Part Number: SAM3N0C
• Manufacturer: Atmel Corporation

10.5.4
10.5.4.1
10.5.4.2
10.5.4.3
58
SAM3N
Software ordering of memory accesses
DMB
DSB
ISB
Table 10-5.
1.
2.
The order of instructions in the program flow does not always guarantee the order of the corre-
sponding memory transactions. This is because:
“Memory system ordering of memory accesses” on page 56
memory system guarantees the order of memory accesses. Otherwise, if the order of memory
accesses is critical, software must include memory barrier instructions to force that ordering. The
processor provides the following memory barrier instructions:
The Data Memory Barrier (DMB) instruction ensures that outstanding memory transactions com-
plete before subsequent memory transactions. See
The Data Synchronization Barrier (DSB) instruction ensures that outstanding memory transac-
tions complete before subsequent instructions execute. See
The Instruction Synchronization Barrier (ISB) ensures that the effect of all completed memory
transactions is recognizable by subsequent instructions. See
Use memory barrier instructions in, for example:
Address range
0xA0000000-
0xBFFFFFFF
0xC0000000-
0xDFFFFFFF
0xE0000000-
0xE00FFFFF
0xE0100000-
0xFFFFFFFF
• the processor can reorder some memory accesses to improve efficiency, providing this does
• the processor has multiple bus interfaces
• memory or devices in the memory map have different wait states
• some memory accesses are buffered or speculative.
• Vector table. If the program changes an entry in the vector table, and then enables the
• Self-modifying code. If a program contains self-modifying code, use an ISB instruction
not affect the behavior of the instruction sequence.
corresponding exception, use a DMB instruction between the operations. This ensures that if
the exception is taken immediately after being enabled the processor uses the new exception
vector.
immediately after the code modification in the program. This ensures subsequent instruction
execution uses the updated program.
See
The Peripheral and Vendor-specific device regions have no additional access constraints.
“Memory regions, types and attributes” on page 55
Memory region share ability policies (Continued)
Memory region
External device
Private Peripheral
Bus
Vendor-specific
device
(2)
Memory type
Device
Strongly-
ordered
Device
“DMB” on page
(1)
(1)
(1)
for more information.
“DSB” on page
“ISB” on page
describes the cases where the
Shareability
Shareable
Non-
shareable
Shareable
-
140.
(1)
(1)
(1)
142.
11011A–ATARM–04-Oct-10
141.
-
-
-