1. Introduction
   1.1. Project/Component Working Name:

	Configuration Variable Defaults
	
   1.2. Name of Document Author/Supplier:

	Eduardo Horvath
	
   1.3. Date of This Document:

	09/10/2007

   1.4. Name of Major Document Customer(s)/Consumer(s):
    1.4.1. The PAC or CPT you expect to review your project:
        HEES PAC
    1.4.2. The ARC(s) you expect to review your project:
        FWARC
    1.4.3. The Director/VP who is "Sponsoring" this project:
        Mike Sanfratello
    1.4.4. The name of your business unit:
        Common Software

   1.5. Email Aliases:
        1.5.1. Responsible Manager: gary.hethcoat@sun.com
        1.5.2. Responsible Engineer: eduardo.horvath@sun.com

2. Project Summary
   2.1. Project Description:
   
	Different platforms may require different defaults for OpenBoot
	configuration variables.  To support this using a common OpenBoot
	image, a new machine descriptor node is defined to provide new
	platform specific default values to Openboot.

3. Business Summary
   3.1. Problem Area:

        Although marketing (and not engineering) dictates these property values,
        they constitute a cross-consolidation software/firmware interface, and
        therefore must be registered with an ARC body.


4. Technical Description:
    4.1. Details:

	Different platforms may require different defaults for OpenBoot
	configuration variables.  To support this using a common OpenBoot
	image, a new machine descriptor node is defined to provide new
	platform specific default values to Openboot.

     4.1.1 Openboot "variables-defaults" MD node

        Name:                   variables-defaults
        Category:               optionally required by root
        Required subordinates:  -
        Optional subordinates:  -

       A new machine descriptor node off of the root node with the name
       "variables-defaults" may be provided.  This node contains a set of
       string properties that correspond to OpenBoot configuration variables.
       These properties indicate the platform specific default values of those
       configuration variables where the platform's default value differs from
       the default value as defined by the OpenBoot binary.  

       When OpenBoot initializes itself it looks for the "variables-defaults"
       node.  If the node is found in the machine descriptor, OpenBoot will
       scan its properties.  OpenBoot will set the default value of each
       configuration variable who's name corresponds to the property name to
       the value of that property.  If OpenBoot finds a property in that node
       that does not correspond to a known configuration variable, that
       property will be silently skipped.

       Note: There is a single OpenBoot binary for all platforms based
       on a particular CPU type. List of configuration variables and their
       default value may be different for OpenBoot binaries created for
       different CPU types. List of configuration variables and their
       default value, as defined by the OpenBoot, are out of scope for this
       case. This case only defines a way for a platform to override the
       default values as defined by the OpenBoot binary. Platform bindings
       should define the contents of "variable-defaults" node if they
       are changing any of the OpenBoot defined defaults.

       The list of variables are represented as properties in the format
       defined below.

       Properties:
         Name           Tag         Required?       Description         
        ----------------------------------------------------------------          
	"var_name"   PROP_STR         No           The variable's default value.
                                                     A NULL terminated string.  
        
	"var_name" is the name of a variable.  Not all variable names are 
	required to be present since only variables which have a unique 
	default value are represented in this node.

        Note: The list of properties (variables) is determined by a platform
        implementation.  Only variables with unique default settings are
        represented in this node.


    4.2. Interfaces:

        Imported Interfaces :

        Interface            Classification	Comments

        sun4v Machine           Sun Private     MD nodes definitions as
        Description nodes                       defined by FWARC/2005/115

        Standard IEEE 1275      Committed       FWARC/1998/392 (see [6])
        configuration variables
                     

        Exported Interfaces :

        "variables-defaults"	Uncommitted	MD node name and properties
                                                as described in section 4.1.1

5. Reference Documents:

    FWARC/2005/115  - Sun4v Machine Description
    FWARC/2006/086  - LDOM Variables