[OE-core] why does using a "revision" prevent downloading during a parse?

[Robert P. J. Day]

  certainly about to embarrass myself again, but from
u-boot_2011.06.bb:

...
# This revision corresponds to the tag "v2011.06"
# We use the revision in order to avoid having to fetch it from the repo during parse
SRCREV = "b1af6f532e0d348b153d5c148369229d24af361a"

PV = "v2011.06+git${SRCPV}"
...

  i don't know what that means -- how does using that "revision"
prevent fetching?  i would simply have defined the SRC_URI using the
tag value, so i'm not sure what benefit i'm getting out of the above.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================