SAM3X8E Atmel Corporation, SAM3X8E Datasheet - Page 70

• Manufacturer Part Number: SAM3X8E
• Manufacturer: Atmel Corporation

11.5.3.1
11.5.4
11.5.4.1
70
70
SAM3X/A
SAM3X/A
Software ordering of memory accesses
Additional memory access constraints for shared memory
DMB
When a system includes shared memory, some memory regions have additional access con-
straints, and some regions are subdivided, as
Table 11-5.
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 68
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
Address range
0x00000000-
0x1FFFFFFF
0x20000000-
0x3FFFFFFF
0x40000000-
0x5FFFFFFF
0x60000000-
0x7FFFFFFF
0x80000000-
0x9FFFFFFF
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.
not affect the behavior of the instruction sequence.
See
The Peripheral and Vendor-specific device regions have no additional access constraints.
“Memory regions, types and attributes” on page 68
Memory region share ability policies
Memory region
Code
SRAM
Peripheral
External RAM
External device
Private Peripheral
Bus
Vendor-specific
device
(2)
(2)
Memory type
Normal
Normal
Device
Normal
Device
Strongly-
ordered
Device
Table 11-5
“DMB” on page
(1)
(1)
(1)
(1)
(1)
(1)
(1)
shows:
for more information.
describes the cases where the
Shareability
-
-
-
-
Shareable
Non-
shareable
Shareable
-
145.
(1)
(1)
(1)
11057A–ATARM–17-Feb-12
11057A–ATARM–17-Feb-12
WBWA
WT
-
-
-
(2)
(2)