Re: Conditional CDL

[Bart Veer <bartv at ecoscentric dot com>]

>>>>> "Gary" == Gary Thomas <gary at mlbassoc dot com> writes:

    Gary> I want to add a new platform which is just a tiny bit
    Gary> different from an existing one.

So you are trying to support both platforms with a single platform HAL
package? 

    Gary> The problem I'm facing is that (this is in the PowerPC HAL)
    Gary> we use CDL interfaces to indicate some properties about
    Gary> platforms to the various variant and architectural layers.
    Gary> In this case, the two platforms expose different interfaces,
    Gary> but that's really the only difference.

    Gary> Concrete info:
    Gary>   platform A:
    Gary>     implements property_X
    Gary>     implements property_Y

    Gary>   platform B:
    Gary>     implements property_Z
    Gary>     implements property_Y

    Gary> The only way I know to do this would be to have a phony
    Gary> cdl_component which has mututally exclusive cdl_options
    Gary> nested within. I don't see any way to make the "implements"
    Gary> statement conditional (at the statement level, only at the
    Gary> component/option level).

    Gary> Similarly, there are the set of "define proc" statements
    Gary> which pass information to RedBoot (like the platform name).
    Gary> I'd like these to be conditional as well.

    Gary> Any good ideas on how I can do this (cleanly)?

"implements" properties belong to a node in the hierarchy, so you will
need separate options for the two platforms. Something like:

  cdl_option platform_A {
      default_value 0
      implements property_X
      implements property_Y
      requires !platform_B
      define_proc {
          ...
      }
  }

  cdl_option platform_B {
      default_value 0
      implements property_Z
      implements property_Y
      requires !platform_A
      define_proc {
          ...
      }
  }

Then have two target entries in ecos.db with appropriate "enable"
lines. Probably one additional line in the platform HAL package:

  cdl_package <whatever> {
      requires platform_A | platform_B
  }

just to make sure that the user does not disable both platforms. There
is no need for a dummy component, these two options could go directly
below the package.

I think that is the cleanest that can be achieved at the moment. I
have thought about an enhanced version of implements, of the form:

   implements_if <expr> <interface>

but I am not sure this would be sufficiently useful generally, and
there would be some problems parsing the property.

For the 2.1 timeframe I would like to extend CDL with cdl_target nodes
which behave largely like options, i.e. they can have requires
properties and the like, but which are also recognised by the admin
tool and result in appropriate entries in a generated ecos.db.

Bart

-- 
Bart Veer                       eCos Configuration Architect
http://www.ecoscentric.com/     The eCos and RedBoot experts