NOVELL TECHNICAL BULLETIN

             TITLE:  Lost and Spurious Interrupts and Netware
      DOCUMENT ID#:  TB.P.293
              DATE:  20 August 1991
           PRODUCT:  NetWare O/S
  PRODUCT REVISION:  v2.x, v3.x
   CROSS-REFERENCE:  N/A

           SYMPTOM:  Lost or Spurious Interrupts Reported

ISSUE/PROBLEM 

Lost or spurious interrupts may be generated by disk and LAN
hardware adapters on file servers with the Intel 80486
microprocessor.  These interrupts may also be generated when the
file server contains a LAN board that has an Intel 82586 LAN
coprocessor.  

A lost interrupt occurs when either the primary or the secondary
programmable interrupt controller (PIC) loses a device's interrupt
request (IRQ) signal before the microprocessor is able to respond
with an interrupt acknowledge (INTA) signal.  A spurious interrupt
occurs when an interrupt service routine (ISR) is called, but the
associated hardware does not need to be serviced.

How NetWare handles lost and spurious interrupts depends on the
NetWare version being used.

NetWare v2.x does not report lost or spurious interrupts.  But
dedicated NetWare v2.15 revision C may hang at load time because of
a lost interrupt on an 80486-based machine.  Hardware interactive
utilities such as VREPAIR may also result in a hang.  Nondedicated
NetWare v2.15 revision C does not exhibit this hang problem.

NetWare v3.10 generates the following system alert each time a lost
interrupt is detected by the primary PIC (IRQ 0-7):  "Interrupt
controller detected a lost hardware interrupt."  With NetWare
v3.10, lost interrupts occurring on the secondary PIC (IRQ 8-15)
are interpreted as spurious interrupts and result in the following
message:  "Spurious hardware interrupt 15 detected."  When an
actual spurious hardware interrupt occurs, the system alert is
"Spurious hardware interrupt xx detected."

NetWare v3.11 reports lost and spurious interrupts the same way as
NetWare v3.10, with the added capability of reporting lost
interrupts on the secondary PIC.  The resulting message in the case
of a lost interrupt on the secondary PIC is "Secondary interrupt
controller detected a lost hardware interrupt."

SOLUTION

If the lost and spurious error messages occur on a file server with
an Intel 80486 microprocessor, the user can obtain a disk or LAN
driver that has been modified to avoid the 80486 lost interrupt
situation.  Users may contact the driver developer for enhanced
drivers addressing these problems.

If lost or spurious error messages occur and an Intel 82586 LAN
coprocessor is visible on a LAN adaptor in the file server, the
user can turn off the display of lost and spurious interrupt
messages as described below.   

For other occurrences of lost and spurious interrupt messages, a
possible solution is to isolate and replace or repair the
responsible hardware or software (as would be done with a GPI or
GPPE error).

With NetWare versions 3.10 and 3.11, the user can disable the
display of lost and spurious interrupt alerts by entering "SET
Display Lost Interrupt Alerts = OFF" and "SET Display Spurious
Interrupt Alerts = OFF" at the file server console.  The default to
these parameters is ON.  Disabling these messages does not stop
lost interrupts from occurring or affect how the operating system
handles lost interrupts; it simply tells the operating system to
not generate the lost interrupt message.  In other words, setting
the Display Lost Interrupt Alerts parameter to ON or OFF does not
affect the functionality of the system.