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

B2.4.7 Exclusive monitors operations
Common Memory System Architecture Features
The SetExclusiveMonitors() function sets the exclusive monitors for a Load-Exclusive instruction. The
ExclusiveMonitorsPass() function checks whether a Store-Exclusive instruction still has possession of the
exclusive monitors and therefore completes successfully.
// SetExclusiveMonitors()
// ======================
SetExclusiveMonitors(bits(32) address, integer size)
memaddrdesc = TranslateAddress(address, CurrentModeIsPrivileged(), FALSE);
if memaddrdesc.memattrs.shareable then
MarkExclusiveGlobal(memaddrdesc.physicaladdress, ProcessorID(), size);
MarkExclusiveLocal(memaddrdesc.physicaladdress, ProcessorID(), size);
// ExclusiveMonitorsPass()
// =======================
boolean ExclusiveMonitorsPass(bits(32) address, integer size)
// It is IMPLEMENTATION DEFINED whether the detection of memory aborts happens
// before or after the check on the local Exclusive Monitor. As a result a failure
// of the local monitor can occur on some implementations even if the memory
// access would give an memory abort.
if address != Align(address, size) then
AlignmentFault(address, TRUE);
else
memaddrdesc = TranslateAddress(address, CurrentModeIsPrivileged(), TRUE);
passed = IsExclusiveLocal(memaddrdesc.paddress, ProcessorID(), size);
if memaddrdesc.memattrs.shareable then
passed = passed && IsExclusiveGlobal(memaddrdesc.paddress, ProcessorID(), size);
if passed then
ClearExclusiveLocal(ProcessorID());
return passed;
The MarkExclusiveGlobal() procedure takes as arguments a FullAddress paddress, the processor identifier
processorid and the size of the transfer. The procedure records that processor processorid has requested
exclusive access covering at least size bytes from address paddress. The size of region marked as exclusive
is IMPLEMENTATION DEFINED, up to a limit of 2KB, and no smaller than two words, and aligned in the
address space to the size of the region. It is UNPREDICTABLE whether this causes any previous request for
exclusive access to any other address by the same processor to be cleared.
MarkExclusiveGlobal(FullAddress paddress, integer processorid, integer size)
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. B2-35