[ltp] X20 fan control notes

[Richard]

Dear All,

I finally got my X20's fan to be silent. Here are a few observations, 
which may help. Feel free to reuse on the wiki.

1)Without any form of intervention, the fan behaviour is this:
    i) Boot up =>  fan off
    ii)Iff the CPU temp ever exceeds 85 degrees (which can happen if CPU 
heavily loaded for a minute) => fan on
    iii)Subsequently, even when the CPU cools as low as 38 degrees, the fan 
never turns off!

This latching behaviour is rather unfortunate!


2)The fan's "whirr" is relatively quiet. However, it is controlled by a 
PWM circuit, which sends short pulses about 10 times/sec. These cause the 
fan to "tick" relatively loudly, and far more annoyingly.


3)One can cure the ticking by adding a 1000uF capacitor across the fan. 
However, I didn't do this because it then makes the (original) peak 
voltage into the (new) average voltage, thereby speeding up the fan.


4)Fan control is possible via ibm_acpi, provided that it is loaded with 
experimental=1.

In Mandriva 2006, I had to modify rc.sysinit, to replace
    for module in /lib/modules....acpi;
    do insmod $module ; done
by
    for module in /lib/modules....acpi;
    do modprobe `basename $module .ko`; done
. Otherwise, you have to rmmod and modprobe it, but that breaks acpid.


5)Both of the following have the same effect, namely to stop the fan for 
about 3 seconds:
    echo "disable" > /proc/acpi/ibm/fan
    echo "enable" > /proc/acpi/ibm/fan
However, the fan will automatically re-engage on its own.

Thus, I have modified the fan script below, which works perfectly on 
the X20, but which would probably be *dangerous* on another model, since 
it relies on a specific bug in the hardware.



6) Result: thinkpad is normally totally inaudible (except for slight 
"chirping" from the CPU itself). If run for over about 60 secs on full 
cpuload, the fan comes on till it cools down.


7)Incidentally:
   a)Reading from the acpi battery status still kills off the nvram - if 
(and only if) the nvram has not been read at least once before the battery 
is read.





[rjn@toffee-pecan ~]$ cat tp-x20-fan2.sh
------------------------------------
#!/bin/sh

# july 2005 Erik Groeneveld, erik@cq2.nl
# It makes sure the fan is on in case of errors
# and only turns it off when all temps are ok.
# Modified by Richard Neill, now ONLY suitable for X20. Might be dangerous
# on other models, since it allows the BIOS to re-initialise the fan.

IBM_ACPI=/proc/acpi/ibm
THERMOMETER=$IBM_ACPI/thermal
FAN=$IBM_ACPI/fan
MAXTRIPPOINT=65
MINTRIPPOINT=55         #was 60
TRIPPOINT=$MINTRIPPOINT
STATUSFILE=/tmp/fanstatus       #So we can run this script redirected to 
/dev/null

if [ ! -e $FAN ]; then
         echo "Sorry, $FAN does not exist. Did you load ibm_acpi with 
experimental=1 ? "
         exit 1
fi

echo fancontrol: Thermometer: $THERMOMETER, Fan: $FAN
echo fancontrol: Current `cat $THERMOMETER`
echo fancontrol: Controlling temperatures between $MINTRIPPOINT and 
$MAXTRIPPOINT degrees.

# Make sure the fan is turned on when the script crashes or is killed
trap "echo enable > $FAN; exit 0" HUP KILL INT ABRT STOP QUIT SEGV TERM

while [ 1 ];
do
         command=enable
         temperatures=`sed s/temperatures:// < $THERMOMETER`
         result=
         for temp in $temperatures
         do
                 test $temp -le $TRIPPOINT && result=$result.Ok
         done
         if [ "$result" = ".Ok.Ok.Ok.Ok.Ok.Ok.Ok.Ok" ]; then
                 #We're cool enough. Disable the fan. But don't sleep too 
long, since
                 #temperature rises very fast. (=> 5sec). Also, we must 
stop the
                 #embedded controller taking over (=> 0.5 sec)
                 echo "disable" > $FAN
                 echo "Fan Off" > $STATUSFILE
                 TRIPPOINT=$MAXTRIPPOINT
                 sleep 0.5
         else
                 #We're too hot!  Enable the fan. Since temperature falls 
quit slowly,
                 #and we want to prevent hunting, sleep for 30 seconds.
                 #BUT, on the X20, a peculiarity is that echoing "enable"
                 #actually stops the fan for a moment! So, echo nothing, 
and let
                 #it start on its own...
                 #echo "enable" > $FAN
                 echo "Fan On" > $STATUSFILE
                 TRIPPOINT=$MINTRIPPOINT
                 sleep 30
         fi
done
-------------------------



Best wishes,

Richard