User guide

Programmers Model
ARM DDI 0337I Copyright © 2005-2008, 2010 ARM Limited. All rights reserved. 3-13
ID072410 Non-Confidential
• System accesses that cross into PPB space do not wrap within System space. For example,
an unaligned halfword access to the last byte of System space (
0xDFFFFFFF ) is converted
by the System interface into a byte access to
0xDFFFFFFF followed by a byte access to
0xE0000000 . 0xE0000000 is not a valid address on the System bus.
• System accesses that cross into Code space do not wrap within System space. For
example, an unaligned halfword access to the last byte of System space (
0xFFFFFFFF ) is
converted by the System interface into a byte access to
0xFFFFFFFF followed by a byte
access to
0x00000000 . 0x00000000 is not a valid address on the System bus.
• Unaligned accesses are not supported to PPB space, and so there are no boundary crossing
cases for PPB accesses.
Unaligned accesses that cross into the bit-band alias regions are also architecturally
Unpredictable. The processor performs the access to the bit-band alias address, but this does not
result in a bit-band operation. For example, an unaligned halfword access to
0x21FFFFFF is
performed as a byte access to
0x21FFFFFF followed by a byte access to 0x22000000 (the first byte
of the bit-band alias).
Unaligned loads that match against a literal comparator in the FPB are not remapped. FPB only
remaps aligned addresses.