1Last reviewed: 06/02/2009
   3                     HP iLO2 NMI Watchdog Driver
   4              NMI sourcing for iLO2 based ProLiant Servers
   5                     Documentation and Driver by
   6              Thomas Mingarelli <>
   8 The HP iLO2 NMI Watchdog driver is a kernel module that provides basic
   9 watchdog functionality and the added benefit of NMI sourcing. Both the
  10 watchdog functionality and the NMI sourcing capability need to be enabled
  11 by the user. Remember that the two modes are not dependent on one another.
  12 A user can have the NMI sourcing without the watchdog timer and vice-versa.
  14 Watchdog functionality is enabled like any other common watchdog driver. That
  15 is, an application needs to be started that kicks off the watchdog timer. A
  16 basic application exists in the Documentation/watchdog/src directory called
  17 watchdog-test.c. Simply compile the C file and kick it off. If the system
  18 gets into a bad state and hangs, the HP ProLiant iLO 2 timer register will
  19 not be updated in a timely fashion and a hardware system reset (also known as
  20 an Automatic Server Recovery (ASR)) event will occur.
  22 The hpwdt driver also has four (4) module parameters. They are the following:
  24 soft_margin - allows the user to set the watchdog timer value
  25 allow_kdump - allows the user to save off a kernel dump image after an NMI
  26 nowayout    - basic watchdog parameter that does not allow the timer to
  27               be restarted or an impending ASR to be escaped.
  28 priority    - determines whether or not the hpwdt driver is first on the
  29               die_notify list to handle NMIs or last. The default value
  30               for this module parameter is 0 or LAST. If the user wants to
  31               enable NMI sourcing then reload the hpwdt driver with
  32               priority=1 (and boot with nmi_watchdog=0).
  34 NOTE: More information about watchdog drivers in general, including the ioctl
  35       interface to /dev/watchdog can be found in
  36       Documentation/watchdog/watchdog-api.txt and Documentation/IPMI.txt.
  38 The priority parameter was introduced due to other kernel software that relied
  39 on handling NMIs (like oprofile). Keeping hpwdt's priority at 0 (or LAST)
  40 enables the users of NMIs for non critical events to be work as expected.
  42 The NMI sourcing capability is disabled by default due to the inability to
  43 distinguish between "NMI Watchdog Ticks" and "HW generated NMI events" in the
  44 Linux kernel. What this means is that the hpwdt nmi handler code is called
  45 each time the NMI signal fires off. This could amount to several thousands of
  46 NMIs in a matter of seconds. If a user sees the Linux kernel's "dazed and
  47 confused" message in the logs or if the system gets into a hung state, then
  48 the hpwdt driver can be reloaded with the "priority" module parameter set
  49 (priority=1).
  51 1. If the kernel has not been booted with nmi_watchdog turned off then
  52    edit /boot/grub/menu.lst and place the nmi_watchdog=0 at the end of the
  53    currently booting kernel line.
  54 2. reboot the sever
  55 3. Once the system comes up perform a rmmod hpwdt
  56 4. insmod /lib/modules/`uname -r`/kernel/drivers/char/watchdog/hpwdt.ko priority=1
  58 Now, the hpwdt can successfully receive and source the NMI and provide a log
  59 message that details the reason for the NMI (as determined by the HP BIOS).
  61 Below is a list of NMIs the HP BIOS understands along with the associated
  62 code (reason):
  64        No source found                00h
  66        Uncorrectable Memory Error     01h
  68        ASR NMI                        1Bh
  70        PCI Parity Error               20h
  72        NMI Button Press               27h
  74        SB_BUS_NMI                     28h
  76        ILO Doorbell NMI               29h
  78        ILO IOP NMI                    2Ah
  80        ILO Watchdog NMI               2Bh
  82        Proc Throt NMI                 2Ch
  84        Front Side Bus NMI             2Dh
  86        PCI Express Error              2Fh
  88        DMA controller NMI             30h
  90        Hypertransport/CSI Error       31h
  94 -- Tom Mingarelli
  95    (
  96 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.