************************************************************************
*                     HOW TO MODIFY THE DSDT FILE                      *
*                                                                      *
*            Alessio Signorini <alessio-signorini@uiowa.edu>           *
*                                                                      *
*                         27th of August 2005                          *
************************************************************************





[A] Tools that you need ------------------------------------------------

   IASL
      http://www.intel.com/technology/iapc/acpi/downloads.htm

   PM-TOOLS (acpidump)
      http://ftp.kernel.org/pub/linux/kernel/people/lenb/acpi/utils/





[B] Obtain your DSDT ---------------------------------------------------
You can obtain the DSDT of your machine in two ways:

1) If the file "/proc/acpi/dsdt" exists, just use the unix command

   cat /proc/acpi/dsdt > dsdt.aml

to save it into the file DSDT.AML.

2) Use the utility ACPIDUMP of the PM-TOOLS writing on the prompt

   acpidump -t DSDT -b > dsdt.aml





[C] Decompile your DSDT ------------------------------------------------
Use  the software IASL to decompile it and obtain the assembler that you
will modify. At the console prompt write

   iasl -d dsdt.aml

to obtain the decompiled file DSDT.DSL.





[D] Obtain your trip-points --------------------------------------------
At the console prompt write

   cat /proc/acpi/thermal_zone/THRM/trip_points

then convert those values in HEX code using a whatever calculator. In my
system they are 45 (2D in hex) and 75 (4B in hex).





[E] Edit the disassembled file -----------------------------------------
With  a  text  editor  as  NEDIT or GEDIT or VI find those values in the
disassembled  file  DSDT.DSL. Look for something like 0x2D or 0x4B in my
cases.

In my case I found them in a part of code like this

   Method (_AC0, 0, Serialized)
   {
      Store (0x2D, Local0)
      Return (Add (0x0AAC, Multiply (Local0, 0x0A)))
   }

Your  one  may differ. However, modify the found value with the HEX code
of  the  new  temperature  that  you  would  like (for example 35 degree
Celsius are represented by the hex code 23).

When you are done save the file and exit.





[F] Compile the modified disassembled file -----------------------------
At the console prompt write

   iasl -tc dsdt.dsl

to  obtain the file DSDT.HEX that is the one you have to include in your
kernel source code to make it work.





[G] Include DSDT.HEX in the kernel source code -------------------------
Copy the file DSDT.HEX in the directory

   driver/acpi/

of the last kernel source code. Then open with a text editor the file

   osl.c

somewhere before the lines

   #ifdef CONFIG_ACPI_CUSTOM_DSDT
      #include CONFIG_ACPI_CUSTOM_DSDT_FILE
   #endif

you have to write something like

   #define CONFIG_ACPI_CUSTOM_DSDT
   #define CONFIG_ACPI_CUSTOM_DSDT_FILE "dsdt.hex"

Then delete the file OSL.O if it exists and recompile your kernel.