WatchdogTimer

Function Table

Address	Name	Description
	WatchdogTimerDriverEntryPoint
	WatchdogTimerNotifyHandler
	WatchdogTimerRegisterHandler
	WatchdogTimerSetTimerPeriod
	WatchdogTimerGetTimerPeriod
	DebugAssertPrint
	DebugAssert
	SmmCommunicationSend
	ReadUnaligned64
	HobCompareGuidEntry
Protocol	GUIDs
EFI_WATCHDOG_TIMER_ARCH_PROTOCOL_GUID	/// {665E3FF5-46CC-11D4-9A38-0090273FC14D}
EFI_GUID	gEfiWatchdogTimerArchProtocolGuid =
gEfiHobListGuid	/// {7739F24C-93D7-11D4-9A3A-0090273FC14D}
EFI_GUID	gEfiHobListGuid =
gEfiSmmCommunicationProtocolGuid	/// {D2B2B828-0826-48A7-B3DF-983C006024F0}
EFI_GUID	gEfiSmmCommunicationProtocolGuid =
gEfiGenericMemTestPatternGuid	(HOB GUID for debug output device)
EFI_GUID	gEfiGenericMemTestPatternGuid =
Global	Variables
The	EFI_WATCHDOG_TIMER_ARCH_PROTOCOL instance installed on the handle.
Contains	function pointers for RegisterHandler and SetTimerPeriod.
The	third field (GetTimerPeriod) is overlapped with mWatchdogTimerPeriod.
EFI_WATCHDOG_TIMER_ARCH_PROTOCOL	mWatchdogTimerProtocol = {
GetTimerPeriod	is implicitly at &mWatchdogTimerPeriod
Stores	the current watchdog timer period in 100ns units.
Initialized	to WATCHDOG_TIMER_DEFAULT_PERIOD (1500 = 150us).
This	also aliases with the third entry of the protocol structure
allowing	GetTimerPeriod to return the period value directly.
UINT64	mWatchdogTimerPeriod = WATCHDOG_TIMER_DEFAULT_PERIOD;
Pointer	to the registered watchdog notification function, or NULL.
VOID	*mWatchdogNotifyFunction = NULL;
Flag	indicating whether a watchdog notification handler is registered.
VOID	*mWatchdogNotifyRegistered = NULL;
Cached	pointer to the HOB list, obtained from the system configuration table.
VOID	*mHobList = NULL;
Cached	pointer to the SMM Communication Protocol interface.
VOID	*mSmmCommunicationProtocol = NULL;
NMI	flag byte. Accessed via CMOS I/O ports 0x70/0x71.
Bit	layout: bit 7 of CMOS index 0x4B stores an NMI status value.
UINT8	mNmiFlag = 0;
Function	Implementations
Initialize	UEFI global variables (gImageHandle, gST, gBS, gRT)
gImageHandle	= ImageHandle;
Initialize	the HOB list
GetHobList	();
Install	the EFI_WATCHDOG_TIMER_ARCH_PROTOCOL
Status	= gBS->LocateProtocol (
Protocol	already installed	this is unexpected
DebugAssert	(
Allocate	pool for the protocol interface structure
EfiBootServicesData	type, 16 bytes (2 function pointers)
Status	= gBS->AllocatePool (
Initialize	the protocol structure
is	aliased at the same offset as the third protocol function pointer.
Install	the protocol on the image handle
Status	= gBS->InstallMultipleProtocolInterfaces (
Send	SMM communication to update SMM watchdog handler state
Invoke	registered notify function if present
if	(mWatchdogNotifyRegistered != NULL) {
Log	the reset event
Reset	the system
if	(NotifyFunction != NULL) {
Check	if handler is already registered
if	(mWatchdogNotifyRegistered == NULL) {
mWatchdogNotifyRegistered	*= (VOID )NotifyFunction;**
Store	the period value (aliased with the GetTimerPeriod function pointer)
mWatchdogTimerPeriod	= TimerPeriod;
Program	the hardware timer
return	gBS->SetTimer (
Return	cached value if already initialized
DebugDevice	= mHobList;
Allocate	a buffer from EFI HOB space to read the HOB entry
HobSize	= (UINTN)gBS->GetHobList ();
HOB	is too small or invalid; return NULL
return	NULL;
Locate	the debug output device via protocol lookup
DebugDevice	= NULL;
Cache	the result
mHobList	= DebugDevice;
Get	the debug output device
DebugDevice	= GetDebugOutputDevice ();
Read	CMOS NMI flag to determine assert severity
Step	1: Save current CMOS index, mask to keep NMI enabled
SavedIndex	= IoRead8 (0x70);
Step	2: Read the NMI status value at CMOS index 0x4B
NmiValue	= IoRead8 (0x71);
Step	3: Determine effective error level from NMI value
NmiStatus	= NmiValue;
If	NMI value is zero, read from fixed memory location
NmiStatus	= ((volatile UINT8 )0xFDAF0490) & 2	1;**
Map	NMI status to error level:
NmiStatus	== 1 -> EFI_ERROR_MAJOR (0x80000004)
NmiStatus	!= 1 -> EFI_ERROR_MINOR (0x80000006)
if	((NmiStatus - 1) <= 0xFD) {
DEBUG_WARN	/ DEBUG_ERROR level
EFI_D_ERROR	(major)
EFI_D_WARN	(minor)
Check	if the determined error level matches the caller's mask
if	((EffectiveErrorLevel & ErrorLevel) != 0) {
Dispatch	to debug output device
PrintFunction	*= (DEBUG_PRINT_ASSERT_FUNCTION)((DEBUG_PRINT_PROTOCOL )DebugDevice)->Print;**
Call	the device's assert function
AssertFunction	*= (DEBUG_ASSERT_FUNCTION)((DEBUG_PRINT_PROTOCOL )DebugDevice)->Assert;**
if	(mHobList != NULL) {
Initialize	to failure state
Get	the number of configuration table entries
TableCount	= gST->NumberOfTableEntries;
Walk	the configuration table looking for gEfiHobListGuid
ConfigTable	= gST->ConfigurationTable;
HobEntry	= ConfigTable[Index].VendorTable;
HOB	list not found	generate assert
Use	cached protocol if available
SmmComm	*= (EFI_SMM_COMMUNICATION_PROTOCOL )mSmmCommunicationProtocol;**
Send	the watchdog command via SMM communication
CommSize	= sizeof (SMM_COMMUNICATION_BUFFER);
First	call: validate Boot Services table
if	(gBS == NULL) {
Locate	the SMM Communication Protocol
Cache	the protocol pointer
mSmmCommunicationProtocol	*= (VOID )SmmComm;**
Read	the first 8 bytes of each GUID
EntryGuidPart1	= ReadUnaligned64 (Entry);
Read	the second 8 bytes of each GUID
EntryGuidPart2	*= ReadUnaligned64 ((UINT8 )Entry + 8);**
Compare	both 64-bit halves
return	(BOOLEAN)(EntryGuidPart1 == ExpectedGuidPart1 &&

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