UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 20 December 2013 741 of 841
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 user guide
The memory map has two 32MB alias regions that map to two 1MB bit-band regions:
• accesses to the 32MB SRAM alias region map to the 1MB SRAM bit-band region, as
shown in Table 636
• accesses to the 32MB peripheral alias region map to the 1MB peripheral bit-band
region, as shown in Table 637
.
Remark: 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 146
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).
Table 636. 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 -
0x23FFFFFF0
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 637. 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 -
0x44FFFFFF
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.
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