[yocto] devtool and adding specific tag from repo

[Brian Kurle]

I'm trying to get up to speed on devtool.

I've created a generic eSDK (poky and meta-openembedded) and installed it.

>From there, I'm trying to create a new recipe, but I apparently am not
executing it correctly to pull the desired tag.

If I execute:

devtool add --version 2.4.2 mbedtls git at github.com:ARMmbed/mbedtls.git

or 

devtool add --version 2.4.2 mbedtls git at github.com:ARMmbed/mbedtls.git;tag=mbedtls-2.4.2

or 

devtool add --version mbedtls-2.4.2 mbedtls git at github.com:ARMmbed/mbedtls.git

It still manages to get the wrong hash (not even the right branch).

Is this a limitation of devtool, or is a better way to do this?
(E.g., just go to the sources directory, check it out and manually update the
recipe?)

My goal is to set up a stock recipe off of the mbedtls-2.4.2 tag,
where I'll then create a bbappend to add additional patches and configuration
specific for our platform.  I could do it manually, but it would be nice to
know how to do it "the right way" for the documentation I'll pass to others on
my team.

Guidance and correction would be most appreciated.

Thanks,

brian