Atmel SAM4S Series, Preliminary Data Sheet

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64
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
MPU Programming
Use a DSB followed by an ISB instruction or exception return to ensure that the new MPU con-
figuration is used by subsequent instructions.
11.4.2.5 Bit-banding
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 1 MB of the SRAM and peripheral memory regions.
The memory map has two 32 MB alias regions that map to two 1 MB bit-band regions:
• accesses to the 32 MB SRAM alias region map to the 1 MB SRAM bit-band region, as shown
in Table 11-6 .
• accesses to the 32 MB peripheral alias region map to the 1 MB peripheral bit-band region, as
shown in Table 11-7 .
Notes: 1. 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.
2. Bit-band accesses can use byte, halfword, or word transfers. The bit-band transfer size
matches the transfer size of the instruction making the bit-band access.
The following formula shows how the alias region maps onto the bit-band region:
bit_word_offset = (byte_offset x 32) + (bit_number x 4)
bit_word_addr = bit_ban bit_word_offset
where:
•
Bit_word_offset
is the position of the target bit in the bit-band memory region.
•
Bit_word_addr
is the address of the word in the alias memory region that maps to the
targeted bit.
Table 11-6. SRAM Memory Bit-banding Regions
Address
Range Memory
Region
Instruction and Data Accesses
0x20000000-
0x200FFFFF
SRAM bit-band
region
Direct accesses to this memory range behave as SRAM
memory accesses, but this region is also bit-addressable
through bit-band alias.
0x22000000-
0x23FFFFFF
SRAM 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.
Table 11-7. Peripheral Memory Bit-banding Regions
Address
Range Memory
Region
Instruction and Data Accesses
0x40000000-
0x400FFFFF
Peripheral bit-band
alias
Direct accesses to this memory range behave as
peripheral memory accesses, but this region is also bit-
addressable through bit-band alias.
0x42000000-
0x43FFFFFF
Peripheral bit-band
region
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.