BLE Split Link Layer

[carlescufi]

The "split link layer" is a version of the BLE controller which is split into:

• An upper, HW independent, LL (ULL)
• A lower, thin, LL (LLL), which depends on the particular HW being used

Currently this split LL is part of the master branch code, but is disabled (CONFIG_BT_LL_SW_SPLIT)

---

This is the list of the missing features to reach parity with the old LL.

• Build the split Link Layer in Zephyr CI (Bluetooth: tests : Include building the LL split in CI #12689)
• Add support for Data Length Extensions (Bluetooth: controller: Data Length Update port to ULL/LLL arch #13235): @cvinayak
• Add support for privacy (in platforms with HW address acceleration) (Bluetooth: Controller privacy support (platforms with HW acceleration) #14675)
• Merge the new Link Layer into master (Bluetooth: controller: Introduce ULL LLL architecture #12404)
• Encapsulate the req/ack code blocks into helper functions (link)
• Update/improve controller documentation

---

Once parity is reached, this new link layer will be the default. The current target is for release 1.15
Additional improvements are listed in #13519.

[carlescufi]

CC @jhedberg @Vudentz @mtpr-ot @thoh-ot @wopu-ot @pskhansen @koffes

[jhedberg]

Does the new controller support Advertising Extensions "out of the box"? If not, that should be added to the list as well, I suppose.

[carlescufi]

@jhedberg it doesn't, but this list is really about reaching feature parity with the existing Link Layer. We already have a GitHub issue for AE.

[SebastianBoe]

Out of curiosity, is "remove old link layer" in the road map, or is the intention to support both?

[jhedberg]

@jhedberg it doesn't, but this list is really about reaching feature parity with the existing Link Layer. We already have a GitHub issue for AE.

@carlescufi ok, thanks for clarifying. I think "Add support for Mesh Extensions" confused me, since that's not really (at least fully) supported in the old LL either.

[aescolar]

Out of curiosity, is "remove old link layer" in the road map

@SebastianBoe : Eventually yes, but the 1st step is to get the split LL to match its functionality

[koffes]

@carlescufi @cvinayak if possible, please break down some more of the issues defined here in smaller tasks. Encapsulate the req/ack in PR #12681 was a nice bite size for getting started.

[koffes]

FYI: I am currently implementing atomic_cas as discussed above.