[ale] Strange kernel message

Tom Wiencko tew at wiencko.com
Sat Sep 21 13:31:19 EDT 2002


A little computer trivia/history from the old guy here...

NMI is the signal line into a CPU which causes a "Non-Maskable 
Interrupt."  What that means is that there are a variety of ways that
an external device can get the attention of the CPU, typically by
asserting a given signal line called an "interrupt."  This causes
the CPU to stop what it is doing and execute a special routine, called
an "interrupt service routine" to see what the device needs to have
done.

While an interrupt service routine (ISR) is executing, the rest of the 
interrupt process is turned off until the routine releases other 
interrupts to be recognized (because it causes all sorts of problems
for ISRs to themselves be interrupted).  This is "disabling" 
interrupts.  There are also mechanisms that allow certain groups of
interrupts to be temporarily disabled (for similar reasons).  This is
called "masking" interrupts.

There is one interrupt that cannot be masked or disabled, typically
because it will be used to handle very, very high priority external
events (like power failure).  This interrupt line is called
"Non-Maskable" and its usual label on the chip itself is "NMI" for
Non-Maskable Interrupt.  It can actually be used for anything (including
"wake-on-LAN") but its use is typically restricted to unusual events
that circumvent normal processor interrupt handling.

Tom


Matthew Brown wrote:
> 
> Isn't NMI "Network Management Interface"?  I thought this was doing a
> Wake-On-Network type of thing for rebooting, etc. from a network
> management interface.  Maybe I'm WAAAAAY off here.
> 
-- 
------------------------------------------------------------------------
Tom Wiencko                                              tew at wiencko.com
President - Wiencko & Associates, Inc.                    (404) 255-2330
Telecom Consulting & Project Development -- Wireline, Wireless, Internet

---
This message has been sent through the ALE general discussion list.
See http://www.ale.org/mailing-lists.shtml for more info. Problems should be 
sent to listmaster at ale dot org.






More information about the Ale mailing list