Re: Power Button on PWS

From: Michael Unger (spam.to.unger_at_spamgourmet.com)
Date: 02/29/04 

Date: Sun, 29 Feb 2004 13:22:45 +0100

On 2004-02-29 08:31, "sms@antinode.org" wrote:

> [...]
>
> There's an always-on stand-by 5V supply output ("+5VSB") to run the
> logic for the power control (manual switch, wake-on-LAN, wake-on-modem,
> et c.), and a (TTL) control input ("PS_ON#"), which, when pulled low,
> causes the other outputs to come on.
>
> As both power button switch contacts appear to be used (unlike the
> simple NO reset button switch), I'd guess that it's being nicely
> debounced, and then used to control a toggle-flip-flop which drives the
> PS_ON# input. As the console can also switch it off, it might feed a
> set/reset input on the same flip-flop, or it could be a bit more
> complicated.
>
> If the flip-flop were waiting for an appropriate clock edge, a
> permanently pressed power button would not do the job.

There's no need for an explicite "clock" -- most flip-flops are "edge
triggered", i.e., they change the output state if an(y) input signal
changes the level from "high" to "low" or vice versa.

> It would take a bit of research to puzzle out the details, and I'm
> not eager to rip that far into my system just now. If my guesses are
> correct, I don't see an easy way to modify the current switch to provide
> an automatic-on capability. As it needs to be in the stuff run by the
> stand-by power supply, I also don't see how the console firmware could
> control such a feature.

One possibility are console variables (or simply flag bits) stored in a
NVRAM and read during the initialization phase perhaps.

> [...]
>
> If the capability was designed in, it should be easy to control (only
> knowledge required). If not, adding it could be pretty tough.

Indeed.

> [...]
>
> Anyone with a diagram of the riser card is, of course, welcome to
> contribute.

No, sorry.

Michael 

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