[Tfug] APM mechanisms

[Bexley Hall]

Hi,

I have a Compaq Presario 3020 (?) that I am
currently using as my DNS/TFTP/SMTP/whatever
server.  It's a Pentium 166 (?) class machine.
Nothing spectacular.  Except, it has two slots
which lets me cram a dual NIC and a SCSI HBA
into it (the dual NIC lets it act as my
firewall and the HBA lets me attach external
storage as well as tape backup, etc. as needed).

But, the *biggest* win is an attached LCD display
which saves me the hassle of having to make room
for a monitor *or* run it headless and have to
drag out a monitor when/if it dies, etc.

The box runs NetBSD 3.1 (quite nicely).  *But*,
the damn LCD backlight is *always* on!  :<

So, with all this as background information,
my question is:

How does APM work on these boxes?

I would assume it is implemented in the BIOS
(since the mechanics of it would obviously vary
from machine to machine).

But, how/when/why does the kernel talk to that
part of the BIOS.  I.e., how does it decide the
machine should go into standby?  I mean, the
machine is never truly *idle*.  E.g., cron
ticks off every few minutes, there are frequent
DNS requests made of it, etc.

And, is the APM API fat enough that it includes
hooks for various "devices" so the caller
(i.e. the kernel) can specify *what* to "wind
down"?  (e.g., "put disk into standby mode",
"put display into standby mode", "put ... ").
Or, does the BIOS author decide what "standby
mode" entails and the kernel can just say
"invoke THE standby mode" or "invoke THE
sleep mode", etc.?

<shrug>  I want to get a feel for how it
*should* be working before I decide if it is
"broken" (misconfigured) or not.

N.B. It may be easier for me to just put a switch
in series with the CCFL's than to deal with
sorting out stuff in the BIOS, etc.

(Note that I haven't found anything in the
machine's "setup" that would pertain to this)

Thx,
--don


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