ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Common Memory System Architecture Features
)
FullAddress paddress
// Access permissions descriptor
type Permissions is (
bits(3) ap, // Access Permission bits
bit xn // Execute Never bit
)
B2.4.2 Basic memory accesses
The _Mem[] function performs single-copy atomic, aligned, little-endian memory accesses to the underlying
physical memory array of bytes:
bits(8*size) _Mem[AddressDescriptor memaddrdesc, integer size]
assert size == 1 || size == 2 || size == 4 || size == 8;
_Mem[AddressDescriptor memaddrdesc, integer size] = bits(8*size) value
assert size == 1 || size == 2 || size == 4 || size == 8;
This function addresses the array using memaddrdesc.paddress,that supplies:
A 32-bit physical address.
An 8-bit physical address extension, that is treated as additional high-order bits of the physical
address. This extension is always 0b00000000 in the PMSA.
A single NS bit to select between Secure and Non-secure parts of the array. This bit is always 0 if the
Security Extensions are not implemented.
The actual implemented array of memory might be smaller than the 2 41 bytes implied. In this case, the
scheme for aliasing is IMPLEMENTATION DEFINED, or some parts of the address space might give rise to
external aborts. For more information, see:
External aborts on page B3-45 for a VMSA implementation
External aborts on page B4-15 for a PMSA implementation.
The attributes in memaddrdesc.memattrs are used by the memory system to determine caching and ordering
behaviors as described in Memory types and attributes and the memory order model on page A3-24.
B2.4.3 Interfaces to memory system specific pseudocode
The following functions call the VMSA-specific or PMSA-specific functions to handle Alignment faults
and perform address translation.
// AlignmentFault()
// ================
AlignmentFault(bits(32) address, boolean iswrite)
case MemorySystemArchitecture() of
when MemArch_VMSA AlignmentFaultV(address, iswrite);
B2-30 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B