Answer
Question: I have a working project on a custom board that contains the SaBLE-x chip. The software used TI's 2.1 stack. Now, we need to support BLE 4.2 protocol so the question is: Can TI's 2.2 stack be used with the SaBLE-x. If yes, do you have any instructions?
Answer: Please refer to the following resources.
http://focus.ti.com/download/freetools/release_notes_BLE_Stack_2_2_1.html
https://e2e.ti.com/support/wireless_connectivity/bluetooth_low_energy/f/538/p/536980/1955602