SAM3N0C Atmel Corporation, SAM3N0C Datasheet - Page 59

• Manufacturer Part Number: SAM3N0C
• Manufacturer: Atmel Corporation

10.5.5
11011A–ATARM–04-Oct-10
Bit-banding
Memory accesses to Strongly-ordered memory, such as the system control block, do not require
the use of DMB instructions.
A bit-band region maps each word in a bit-band alias region to a single bit in the bit-band region.
The bit-band regions occupy the lowest 1MB of the SRAM and peripheral memory regions.
The memory map has two 32MB alias regions that map to two 1MB bit-band regions:
Table 10-6.
Table 10-7.
A word access to the SRAM or peripheral bit-band alias regions map to a single bit in the SRAM
or peripheral bit-band region.
The following formula shows how the alias region maps onto the bit-band region:
Address
range
0x20000000-
0x200FFFFF
0x22000000-
0x23FFFFFF
Address
range
0x40000000-
0x400FFFFF
0x42000000-
0x43FFFFFF
• Memory map switching. If the system contains a memory map switching mechanism, use a
• Dynamic exception priority change. When an exception priority has to change when the
• Using a semaphore in multi-master system. If the system contains more than one bus
• accesses to the 32MB SRAM alias region map to the 1MB SRAM bit-band region, as shown
• accesses to the 32MB peripheral alias region map to the 1MB peripheral bit-band region, as
DSB instruction after switching the memory map in the program. This ensures subsequent
instruction execution uses the updated memory map.
exception is pending or active, use DSB instructions after the change. This ensures the
change takes effect on completion of the DSB instruction.
master, for example, if another processor is present in the system, each processor must use
a DMB instruction after any semaphore instructions, to ensure other bus masters see the
memory transactions in the order in which they were executed.
in
shown in
bit_word_offset = (byte_offset x 32) + (bit_number x 4)
Table 10-6
Table
SRAM memory bit-banding regions
Peripheral memory bit-banding regions
Memory
region
SRAM bit-band
region
SRAM bit-band alias
Memory
region
Peripheral bit-band
alias
Peripheral bit-band
region
10-7.
Instruction and data accesses
Direct accesses to this memory range behave as SRAM
memory accesses, but this region is also bit addressable
through bit-band alias.
Data accesses to this region are remapped to bit band
region. A write operation is performed as read-modify-write.
Instruction accesses are not remapped.
Instruction and data accesses
Direct accesses to this memory range behave as peripheral
memory accesses, but this region is also bit addressable
through bit-band alias.
Data accesses to this region are remapped to bit band
region. A write operation is performed as read-modify-write.
Instruction accesses are not permitted.
SAM3N
59