How to initialize build environment from existing stable image?

[moeller0]

I want to test a few modifications to package/ltq-vdsl-app (I am trying to get access to the retransmission counters, as for modern VDSL2 links in the UK and in Germany ReTx is the norm and these are pretty diagnostic for marginal/bad links). Now, ideally I want to intialize my build environment to match the current 19.07.0 for BT_HomeHub5A stable image, so that in effect, if my changes work out, I can flash the image omto the router with just the single desired change to the ltq-vdsl-app package.
Now my question, given (https://downloads.openwrt.org/releases/19.07.0/targets/lantiq/xrx200/) and the Supplementary Files at the same link, how can I quickly get into the business of building my own 19.07.0 images for lantiq/xrx200?

[tmomas]

Does this help?

Checkout a tagged release's source code (like v21.02.0)

The advice is valid for the 17.01.1 release: $ git fetch --tags remote: Counting objects: 42, done. remote: Total 42 (delta 27), reused 27 (delta 27), pack-reused 15 Unpacking objects: 100% (42/42), done. From https://github.com/lede-project/source * [new tag] v17.01.0 -> v17.01.0 * [new tag] v17.01.0-rc1 -> v17.01.0-rc1 * [new tag] v17.01.0-rc2 -> v17.01.0-rc2 * [new tag] v17.01.1 -> v17.01.1 $ git checkout v17.01.1 Note: che…

[moeller0]

Excellent, that worked well!