uefi中使用watchdog

最新推荐文章于 2025-05-25 05:57:01 发布

tiantao2012

最新推荐文章于 2025-05-25 05:57:01 发布

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本文详细介绍了如何在UEFI环境中使用Watchdog定时器。通过具体代码示例展示了如何设置定时器周期，以及如何取消正在运行的Watchdog定时器。此外，还解释了在不同条件下Watchdog定时器的实现机制。

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一般要在uefi中使用watchdog，会按照如下格式。

gBS->SetWatchdogTimer (5 * 60, 0x0000, 0x00, NULL);

XXXXXXXXXXXX

gBS->SetWatchdogTimer (0x0000, 0x0000, 0x0000, NULL);
即首先调用gBS->SetWatchdogTimer (5 * 60, 0x0000, 0x00, NULL);来是指5分钟到期的watchdog，如果事情在5分钟之内做完，就调用
gBS->SetWatchdogTimer 来关掉watchdog
gBS->SetWatchdogTimer 其实指向的是WatchdogSetTimerPeriod这个函数.
EFI_STATUS
EFIAPI
WatchdogSetTimerPeriod (
IN CONST EFI_WATCHDOG_TIMER_ARCH_PROTOCOL   *This,
IN UINT64                                   TimerPeriod   // In 100ns units
)
{
UINTN       SystemCount;
EFI_STATUS Status;

if (TimerPeriod == 0) {
    mNumTimerTicks = 0;
    return WatchdogDisable ();
}

// Work out how many timer ticks will equate to TimerPeriod
mNumTimerTicks = (mTimerFrequencyHz * TimerPeriod) / TIME_UNITS_PER_SECOND;

//
// If the number of required ticks is greater than the max number the
// watchdog's offset register (WOR) can hold, we need to manually compute and
// set the compare register (WCV)
//
if (mNumTimerTicks > MAX_UINT32) {
    //
    // We need to enable the watchdog *before* writing to the compare register,
    // because enabling the watchdog causes an "explicit refresh", which
    // clobbers the compare register (WCV). In order to make sure this doesn't
    // trigger an interrupt, set the offset to max.
    //
    Status = WatchdogWriteOffsetRegister (MAX_UINT32);
    if (EFI_ERROR (Status)) {
      return Status;
    }
    WatchdogEnable ();
    SystemCount = ArmGenericTimerGetSystemCount ();
    Status      = WatchdogWriteCompareRegister (SystemCount + mNumTimerTicks);
} else {
    Status = WatchdogWriteOffsetRegister ((UINT32)mNumTimerTicks);
    WatchdogEnable ();
}

return Status;
}
可以看到，如果TimerPeriod==0，就调用WatchdogDisable 关掉watchdog.正常情况下设定的watchdog到期时间不会超过MAX_UINT32。因此首先调用将TimerPeriod 转成ticks
mNumTimerTicks = (mTimerFrequencyHz * TimerPeriod) / TIME_UNITS_PER_SECOND;
然后写寄存器
Status = WatchdogWriteOffsetRegister ((UINT32)mNumTimerTicks);
最后enable watchdog
    WatchdogEnable ();

在dxemain.c 中
(EFI_SET_WATCHDOG_TIMER)                      CoreSetWatchdogTimer,                     // SetWatchdogTimer
会注册SetWatchdogTimer的回调函数为CoreSetWatchdogTimer

EFI_STATUS
EFIAPI
CoreSetWatchdogTimer (
IN UINTN    Timeout,
IN UINT64   WatchdogCode,
IN UINTN    DataSize,
IN CHAR16   *WatchdogData OPTIONAL
)
{
EFI_STATUS Status;

//
// Check our architectural protocol
//
if (gWatchdogTimer == NULL) {
    return EFI_NOT_AVAILABLE_YET;
}

//
// Attempt to set the timeout
//
Status = gWatchdogTimer->SetTimerPeriod (gWatchdogTimer, MultU64x32 (Timeout, WATCHDOG_TIMER_CALIBRATE_PER_SECOND));

//
// Check for errors
//
if (EFI_ERROR (Status)) {
    return EFI_DEVICE_ERROR;
}

return EFI_SUCCESS;
}

所以后面调用gBS->SetWatchdogTimer 就相当于调用CoreSetWatchdogTimer。而在CoreSetWatchdogTimer 中是直接调用gWatchdogTimer->SetTimerPeriod
由于watchdog是在dxemain.c 中才注册的，也就是说只有dxe之后包括bds才可以使用watchdog函数.