Overtemperature warning to users.

[jg]

The XO-1 has an ambient temperature sensor. The CPU has a fixed over temperature cut-out (see the LX specifications). Testing will tell us the typical rise over ambient temperature inside the main housing, and may allow us to warn the user if the over temperature cutout is likely soon.

There may be ways in which we can reduce power dissipation (e.g. reducing backlight and/or codec power dissipation). Whether this will be useful in practice is not clear.

Jordan notes: And multiple temperature levels would be friggin sweet: one for warning, so we could throttle, and one for critical so we could shut down.

[jg]

Note that the Geode LX has facilities to throttle its performance before it reaches its over temperature.

[jg]

Jordan notes that this process is not automatic; we'll have to do this ourselves, as best we can, from estimating the internal temperature of the system. Having a temperature sensor directly for this was ruled out due to cost.

The first step toward implementing this is to have the EC interrupt on ambient temperature change (we don't want a thermal manager, whether in the kernel or in user space have to poll). If suspended, we don't need the EC to interrupt, either: by definition, the system should be cooling.

[jg]

Hmmm...

Mary Lou, Richard: can we please run some of the systems in the environmental chamber dissipating full power to see if we need to bother with this at all? I gather that we've had no problem at idle at 60degrees C or more....

[jg]

So far, no trouble, even in the environmental chamber.

[rsmith]

We have not had any problems with this so I don't feel its necessary.

[mikus]

For what it's worth - I go around feeeling the backs of XOs. Typically they are no more than warm to the touch.

I ran an XO 24/7 for a couple of weeks in an 80 degrees Fahrenheit room - doing continuous floating point calculations (0% idle). It never got more than warm to the touch.