(bobd) added explanatory comments to via686a section

git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@780 7894878c-1315-0410-8ee3-d5d059ff63e0

etc/sensors.conf.eg

@@ -476,9 +476,22 @@ chip "maxilife-as-*"
 
 chip "via686a-*"
 
-# These seem right for my Tyan S1598:
+# VIA is very specific about the voltage sensor inputs, and our labels
+# reflect what they say.  Unfortunately, they are not at all specific about
+# how to convert any of the register values to real units.  Fortunately,
+# Jonathan Yew <j.teh@iname.com> and Alex van Kaam <darkside@chello.nl>
+# came through with some data for temp conversion and formulae for voltage 
+# conversion. However, the conversions should be regarded as our best guess- 
+# YMMV.  If you notice any glaring inaccuracies (eg. by comparing what sensors
+# says to what your BIOS says when you boot up), please let us know so we can
+# improve.
+
+# On the Tyan S1598, the 2.5V sensor reads 0 and is not displayed in the BIOS, 
+# so you may want to ignore it here.
+
     label "2.0V" "CPU core"
-    ignore "2.5V"
+    label "2.5V" "+2.5V"
+    #ignore "2.5V"
     label "3.3V" "I/O"
     label "5.0V" "+5V"
     label "12V" "+12V"
@@ -490,16 +503,39 @@ chip "via686a-*"
     label temp2 "CPU Temp"
     label temp3 "SBr Temp"
 
-# Set some limits:
- 
-    set in0_min 2.1
+# Set your CPU core limits here.  For the other voltage sensors, the 
+# built-in defaults should be fine.
+
+    set in0_min 2.0
     set in0_max 2.5
-    set in1_min 2.5*0.95
-    set in1_max 2.5*1.05
-    set in2_min 3.3*0.90
-    set in2_max 3.3*1.10
-    set in3_min 5.0*0.95
-    set in3_max 5.0*1.05
-    set in4_min 12*0.95
-    set in4_max 12*1.05
- 
+
+# Set your temp limits here.  Remember, 'tempX_over' is the temp at which an
+# alarm is triggered, and 'tempX_hyst' is the temp at which an alarm turns off.
+# Setting tempX_hyst to a few degrees below the corresponding tempX_over 
+# prevents an oscillation between alarm on and off states.  This kind of 
+# oscillation is known as hyteresis, thus the name.  (You typically get the 
+# most serious and troublesome hysteresis when a sensor triggers something to 
+# reduce the temp, thus creating a negative feedback loop.  Even without that,
+# we would still get some oscillation when the temp hovers around the limit 
+# due to noise.)   
+
+    set temp1_hyst 40
+    set temp1_over 45
+    set temp2_hyst 55
+    set temp2_over 60
+    set temp3_hyst 60
+    set temp3_over 65
+
+# You could set your fan limits too, but the defaults should be fine.
+
+    #set fan1_min 5000
+    #set fan2_min 5000
+
+# For at least one Tyan S1598, the following corrections make the sensors
+# readings more in-line with the BIOS readings on boot.  Try these, and 
+# adjust as necessary. 
+
+  #compute "2.0V" 1.02*@ ,  @/1.02
+  #compute "3.3V" 1.02*@  ,  @/1.02
+  #compute "5.0V" 1.009*@  ,  @/1.009
+  #compute "12V" 1.04*@ ,  @/1.04