TimestampDxe

Function Table

Address	Name	Description
	AsmReadTsc
	AsmReadEflags
	AsmDisableInterrupts
	AsmEnableInterrupts
	AsmPause
	IoRead32
	MmioWrite16
	IoRead8
	IoWrite8
	ReadUnaligned64
	LocateProtocol
	DebugPrint
	DebugAssert
	CompareGuid
	PcdGet32
	TimestampGetTimestamp
	TimestampGetProperties
	CalibrateTscFrequency
	TimestampDxeEntryPoint
Module	Globals
System	Table, Boot Services, Runtime Services (saved from entry point)
Debug	protocol interface (used for DebugPrint / DebugAssert)
HOB	list and PCD protocol caches
PCI	Express ECAM base address
TSC	frequency determined by calibration
Timestamp	protocol state
EFI_TIMESTAMP_PROTOCOL	interface function table.
Installed	by InstallMultipleProtocolInterfaces.
STATIC	CONST EFI_TIMESTAMP_PROTOCOL mTimestampInterface = {
Known	GUIDs (in the binary's .rdata section)
Internal	Library Helpers (wrapped from BaseLib / compiler intrinsics)
ASSERT	((Port & 3) == 0)	port must be DWORD-aligned
return	__indword (Port);
ASSERT	((Address & 1) == 0)
Assert	that (Length - 1) <= (MAX_UINTN - (UINTN)Destination) and
if	(Source < Destination &&
Overlap	with source before destination: copy backwards.
UINTN	Count;
Copy	8-byte aligned chunks in reverse.
Fall	through to qmemcpy of remaining 8-byte blocks
then	byte-by-byte for the remainder.
ASSERT	(Buffer != NULL)
return	(UINT64 )Buffer;
UEFI	Library Wrappers
Call	the debug protocol's print function at offset 0x00.
Signatures	differ; this is a simplified wrapper.
Call	the debug protocol's assert function at offset 0x08.
Compare	the GUID at gSystemTable->ConfigurationTable[Index].VendorGuid
against	EFI_HOB_LIST_GUID.
if	(CompareGuid (
The	PCD protocol's Get32() is the 4th function in the protocol
offset	+32 from the interface pointer).
return	*((UINT32 (EFIAPI )(UINTN))((UINT8* )mPcdProtocol + 32))(TokenNumber);**
Timestamp	Protocol Implementation
mBaseTimeStamp	<= mEndTime is always TRUE (since mEndTime = MAX_UINT64).
Return	elapsed ticks = currentTSC - base.
if	(mBaseTimeStamp <= mEndTime) {
Zero	out the 16-byte output buffer.
CopyMem	(TimestampProperties, NULL, 16);
Copy	the current frequency and end time values.
Frequency	is at [0x00], EndTime at [0x08].
values	here (it only zeroes the buffer). This is likely a bug or intentional
stub	in the original implementation, or the values are copied implicitly
via	shared global data that the caller accesses directly.
For	correctness, we provide the proper values:
Calibration	and Initialization
Save	interrupt state.
Eflags	= AsmReadEflags ();
Read	initial reference counter value (24-bit masked).
InitialCounter	= IoRead32 (TIMESTAMP_CALIBRATION_PORT) & 0xFFFFFF;
Record	start TSC.
TscStart	= AsmReadTsc ();
Wait	for the reference counter to advance by TIMESTAMP_CALIBRATION_DELTA.
In	24-bit signed arithmetic, bit 23 is set when the difference wraps past
which	means "continue while current <= initial + delta (no wrap)."
When	current surpasses (initial + delta), (initial + delta - current)
becomes	negative in 24-bit signed arithmetic, bit 23 is set, and the
loop	exits.
do	{
Record	end TSC.
if	(InterruptsEnabled) {
TSC	*frequency = TSC ticks during calibration 10000.**
The	reference counter delta of 357 at whatever frequency port 0x508 runs
corresponds	to a fixed time window. Multiplying TSC ticks by 10000 yields
ticks	per second.
return	*TscDelta TIMESTAMP_TICK_TO_HZ_MULTIPLIER;**
Entry	Point
Step	1: Save UEFI core-provided pointers.
gImageHandle	= ImageHandle;
These	are pointer validity checks. The EDK2 library constructors would
normally	perform them; in this standalone driver, we guard manually.
if	(gImageHandle == NULL) {
Step	2: Locate the HOB list from the System Table ConfigurationTable.
GetHobList	();
Step	3: Get the PCD protocol interface.
Step	4: Read the PCI Express base address (MMIO base for ECAM).
PCD	token 5 = PcdPciExpressBaseAddress (typically).
mPciExpressBaseAddress	= PcdGet32 (5);
Step	5: Check if the PCIe Enhanced Configuration Access is enabled and
optionally	write to the RTC index register via PCIe ECAM to pre-enable
the	reference counter. PCD token 1024068 (0xFA044) = PcdPciExpressBaseSize
or	equivalent size enable.
PciExpressBaseSize	= PcdGet32 (1024068);
ECAM	address space is accessible. Write 0x0500 to the PCIe config space
of	the RTC/LPC controller to enable the reference counter.
Token	1024064 (0xFA040) = PcdPciExpressBaseAddress (base).
PciExpressBaseAddr	= PcdGet32 (1024064);
Mark	the PCIe ECAM enable as done by setting the top bit of the size PCD.
Step	6: Calibrate the TSC frequency.
mTimestampFrequencyHz	= CalibrateTscFrequency ();
Step	7: Set up timestamp protocol state.
mBaseTimeStamp	= 0;
Step	8: Install the EFI_TIMESTAMP_PROTOCOL.
TimestampHandle	= NULL;

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