Watchdog Timer Hardware

The driver implementation described in this document is intended to be as general as possible, but is based on some assumptions about the properties and behavior of timer hardware.

The watchdog timer starts counting down from some settable initial value. When the timer reaches zero, it can either force the OS to restart, or can simply shut down the system. The mechanism used to restart the system is at the discretion of the OEM configuring the Windows Powered server appliance. The watchdog timer operates under the assumption that as long as the OS is running, it continually resets the timer before it can reach zero and fire. The timer device must allow the OS to set the countdown time interval. The timer must support time intervals as small as one second, and as large as five minutes. The timer might support smaller or larger intervals. Such additional support is not required.

The mechanism for restarting the OS is not defined in this documentation.

Microsoft suggests that the watchdog timer hardware provide memory-mapped registers to communicate with the driver. The driver can set the start address of the I/O port or register memory when it allocates the hardware.