Table of Contents
Advertisement
12.5
System interface
12.5.1
Unaligned accesses
12.5.2
Bit-band accesses
12.5.3
Flash Patch remapping
12.5.4
Exclusives
ARM DDI 0337G
Unrestricted Access
The system interface is a 32-bit AHB-Lite bus. Instruction and vector fetches, and data
and debug accesses to the System memory space,
0xE0100000 - 0xFFFFFFFF
For simultaneous accesses to this bus, the arbitration order in decreasing priority is:
•
data accesses
•
instruction and vector fetches
•
debug.
The System bus interface contains control logic to handle unaligned accesses, FPB
remapped accesses, bit-band accesses, and pipelined instruction fetches.
Unaligned data and debug accesses are converted into two or three aligned accesses,
depending on the size and alignment of the unaligned access. This stalls any subsequent
accesses until the unaligned access has completed. For a description of unaligned
accesses, see Access alignment on page 12-11.
Accesses to the bit-band alias region are converted into accesses to the bit-band region.
Bit-band writes take two cycles, they are converted into read-modify-write operations,
and so bit-band write accesses stall any subsequent accesses until the bit-band access
has completed. For a description of bit-band accesses, see Bit-band accesses on
page 12-13.
Accesses to the Code memory space that are remapped to System memory space incur
a cycle penalty to be remapped. This stalls any subsequent accesses until the Flash Patch
access has completed. See FPB on page 11-6 for a description of Flash Patch.
The System bus supports exclusive accesses. This is carried out using two sideband
signals, EXREQS and EXRESPS. For more information, see System bus interface on
page A-10.
For more information about semaphores and the local exclusive monitor see the ARM
Architecture Memory Model chapter in the ARMv7M ARM Architecture Reference
Manual.
Copyright © 2005-2008 ARM Limited. All rights reserved.
, are performed over this bus.
Non-Confidential
0x20000000 - 0xDFFFFFFF
Bus Interface
,
12-7
Advertisement
Table of Contents
