User guide

Programmers Model
ARM DDI 0337I Copyright © 2005-2008, 2010 ARM Limited. All rights reserved. 3-17
ID072410 Non-Confidential
• The alias word at 0x2200001C maps to bit [7] of the bit-band byte at 0x20000000 : 0x2200001C
=
0x22000000 + ( 0 * 32 ) + 7 * 4 .
Figure 3-2 Bit-band mapping
3.7.1 Directly accessing an alias region
Writing to a word in the alias region has the same effect as a read-modify-write operation on the
targeted bit in the bit-band region.
Bit [0] of the value written to a word in the alias region determines the value written to the
targeted bit in the bit-band region. Writing a value with bit [0] set writes a 1 to the bit-band bit,
and writing a value with bit [0] cleared writes a 0 to the bit-band bit.
Bits [31:1] of the alias word have no effect on the bit-band bit. Writing
0x01 has the same effect
as writing
0xFF . Writing 0x00 has the same effect as writing 0x0E .
Reading a word in the alias region returns either
0x01 or 0x00 . A value of 0x01 indicates that the
targeted bit in the bit-band region is set. A value of
0x00 indicates that the targeted bit is clear.
Bits [31:1] are zero.
3.7.2 Directly accessing a bit-band region
You can directly access the bit-band region with normal reads and writes to that region.
0x23FFFFE4
0x22000004
0x23FFFFE00x23FFFFE80x23FFFFEC0x23FFFFF00x23FFFFF40x23FFFFF80x23FFFFFC
0x220000000x220000140x220000180x2200001C 0x220000080x22000010 0x2200000C
32MB alias region
0
7 0
07
0x200000000x200000010x200000020x20000003
6 5 4 3 2 1 07 6 5 4 3 2 1 7 6 5 4 3 2 1 07 6 5 4 3 2 1
07 6 5 4 3 2 1 6 5 4 3 2 107 6 5 4 3 2 1 07 6 5 4 3 2 1
0x200FFFFC0x200FFFFD0x200FFFFE0x200FFFFF
1MB SRAM bit-band region