Non-Maskable interrupts (NMI)

Non-maskable interrupts (NMI) are critical interrupts such as those generated after a power failure that cannot be blocked by the CPU. This is in contrast to most common device interrupts such as disk and network adapter interrupts, which are considered maskable.

When developing drivers for hardware that can generate NMIs, use the DDI routines for efficient handling of these critical interrupts.

DDI coding

Drivers typically call the drv_callback(D3) function to register a callback handler with the system. When NMIs are generated, the registered driver handler is called back, and the drivers can choose to do one or more of the following things:

• Verify whether the NMI is relevant (can be handled by the driver), and if unrelated, return NMI_UNKNOWN.

• Detect the cause, present a user-friendly message, and return NMI_BENIGN.

• If necessary, in addition to detecting the cause, attempt a graceful recovery, and if successful, return NMI_BENIGN.

• If the interrupt is critical or if recovery is unsuccessful, perform a graceful shutdown.

• Finally, if the error is fatal, return NMI_FATAL, which in turn will cause the higher layers to take the appropriate remedial action.

ODDI coding

ODDI drivers use the add_nmi_handler(D3oddi) and remove_nmi_handler(D3oddi) functions to register and remove NMI handler functions.