[yocto] How to specify a default value for a variable in a recipe

[Gary Thomas]

On 2014-06-13 08:07, Patrick Doyle wrote:
> On Fri, Jun 13, 2014 at 9:47 AM, Gary Thomas <gary at mlbassoc.com> wrote:
>> If this is in the gstxbac recipe itself, use the much simpler
>>    SRCREV ?= "${AUTOREV}"
>
> Even better!  While I like that solution best of all, that opens up a
> whole new world of hurt for me.
>
> How does
>
> SRCREV_default_pn-gstxbac = "${AUTOREV}"
>
> work?  When would I use that over the much simpler solution you proposed?
>
> I am thinking that if I used your solution, I might place
>
> SRCREV_pn-gstxbac = "123" (or a git hash, or whatever)
>
> in my local.conf?  in my BSP layer.conf?
>
> I guess I could put
>
> SRCREV_default_pn-gstxbac = "123" in my BSP layer.conf, and then,
> later on, on some other project that used the same board, I might put
>
> SRCREV_pn-gstxbac = "${AUTOREV}" in my local.conf, or maybe in a
> .bbappend file for my BSP?
>
> How/where does the _pn suffix (middlex?) come into play?

Any time you need to set the variable outside of the recipe itself (.bb* or .inc),
then you need the _pn-${recipe} syntax.

>
> At this point, I like your solution tremendously, as it makes sense to
> me.  But I sure would like to understand more about all the myriad
> capabilities offered by bitbake.

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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