Intel Extensible Firmware Interface - Manual (Page 215)

Services — Runtime Services
Version 1.10 12/01/02 6-23
GetNextHighMonotonicCount()
Summary
Returns the next high 32 bits of the platform’s monotonic counter.
Prototype
EFI_STATUS
GetNextHighMonotonicCount (
OUT UINT32 *HighCount
);
Parameters
HighCount Pointer to returned value.
Description
The GetNextHighMonotonicCount() function returns the next high 32 bits of the platform’s
monotonic counter.
The platform’s monotonic counter is comprised of two 32-bit quantities: the high 32 bits and the
low 32 bits. During boot service time the low 32-bit value is volatile: it is reset to zero on every
system reset and is increased by 1 on every call to
GetNextMonotonicCount() . The high
32-bit value is nonvolatile and is increased by 1 whenever the system resets or whenever the low
32-bit count (returned by
GetNextMonoticCount() ) overflows.
The GetNextMonotonicCount() function is only available at boot services time. If the
operating system wishes to extend the platform monotonic counter to runtime, it may do so by
utilizing
GetNextHighMonotonicCount() . To do this, before calling
ExitBootServices() the operating system would call GetNextMonotonicCount() to
obtain the current platform monotonic count. The operating system would then provide an
interface that returns the next count by:
• Adding 1 to the last count.
• Before the lower 32 bits of the count overflows, call
GetNextHighMonotonicCount() .
This will increase the high 32 bits of the platform’s nonvolatile portion of the monotonic count
by 1.
This function may only be called at Runtime.
Status Codes Returned
EFI_SUCCESS The next high monotonic count was returned.
EFI_DEVICE_ERROR The device is not functioning properly.
EFI_INVALID_PARAMETER HighCount is NULL .