Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Table 5-41 Global Lock Structure within the FACS
Field Bit Length Bit Offset Description
Pending 1 0 Non-zero indicates that a request for ownership of the Global
Lock is pending.
Owned 1 1 Non-zero indicates that the Global Lock is Owned.
Reserved 30 2 Reserved for future use.
The following code sequence is used by both OSPM and the firmware to acquire ownership of the
Global Lock. If non-zero is returned by the function, the caller has been granted ownership of the
Global Lock and can proceed. If zero is returned by the function, the caller has not been granted
ownership of the Global Lock, the “pending” bit has been set, and the caller must wait until it is
signaled by an interrupt event that the lock is available before attempting to acquire access again.
Note: In the examples that follow, the “GlobalLock” variable is a pointer that has been previously
initialized to point to the 32-bit Global Lock location within the FACS.
AcquireGlobalLock:
mov ecx, GlobalLock ; ecx = Address of Global Lock in FACS
acq10: mov eax, [ecx] ; Get current value of Global Lock
mov edx, eax
and edx, not 1 ; Clear pending bit
bts edx, 1 ; Check and set owner bit
adc edx, 0 ; If owned, set pending bit
lock cmpxchg dword ptr[ecx], edx ; Attempt to set new value
jnz short acq10
; If not set, try again
cmp dl, 3 ; Was it acquired or marked pending?
sbb eax, eax ; acquired = -1, pending = 0
ret
The following code sequence is used by OSPM and the firmware to release ownership of the Global
Lock. If non-zero is returned, the caller must raise the appropriate event to the other environment to
signal that the Global Lock is now free. Depending on the environment, this signaling is done by
setting the either the GBL_RLS or BIOS_RLS within their respective hardware register spaces. This
signal only occurs when the other environment attempted to acquire ownership while the lock was
owned.
134 April, 2015 Version 6.0