Re: Conditional CDL

[Gary Thomas <gary at mlbassoc dot com>]

On Mon, 2003-03-24 at 09:46, Bart Veer wrote:
> >>>>> "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? 
> 

Yes.  The platforms only differ by the processor which is installed,
and thanks to the wisdom of Motorola, that implies a slightly different
set of peripherals :-(

>     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.
> 

This is about what I thought.  I recall having trouble before with 
having the define_proc nested, but I'll try it again and see how it
goes.

> 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.
> 

I'm not sure how useful this would be in general (outside this case).

> 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.

One thing I've yearned for would be an easier way to conditionalize
the define_proc statements.  For example, I'd like a way to express
the platform clock speed (selected by other CDL) in the lines that
are used by RedBoot, so you could get a platform description like
  PowerPC 850 (48MHz)
or the like.  Is there any good way to do this?

Thanks for your time.

-- 
------------------------------------------------------------
Gary Thomas                 |
MLB Associates              |  Consulting for the
+1 (970) 229-1963           |    Embedded world
http://www.mlbassoc.com/    |
email: <gary at mlbassoc dot com>  |
gpg: http://www.chez-thomas.org/gary/gpg_key.asc
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