Datasheet

67
SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
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:
bit_word_offset = (byte_offset x 32) + (bit_number x 4)
bit_word_addr = bit_band_base + 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.
 Bit_band_base is the starting address of the alias region.
 Byte_offset is the number of the byte in the bit-band region that contains the targeted bit.
 Bit_number is the bit position, 0-7, of the targeted bit.
Figure 10-2 shows examples of bit-band mapping between the SRAM bit-band alias region and the SRAM bit-
band region:
 The alias word at 0x23FFFFE0 maps to bit[0] of the bit-band byte at 0x200FFFFF : 0x23FFFFE0 = 0x22000000 +
(
0xFFFFF *32) + (0*4).
 The alias word at 0x23FFFFFC maps to bit[7] of the bit-band byte at 0x200FFFFF : 0x23FFFFFC = 0x22000000 +
(
0xFFFFF *32) + (7*4).
 The alias word at 0x22000000 maps to bit[0] of the bit-band byte at 0x20000000 : 0x22000000 = 0x22000000 +
(0*32) + (0 *4).
 The alias word at 0x2200001C maps to bit[7] of the bit-band byte at 0x20000000 : 0x2200001C = 0x22000000 +
(0*32) + (7*4).
Table 10-6. 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 10-7. 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.