You cant recover a protected nrf52 with stlink.
"Regarding the protection bit, one thing to be aware of is that the ST-LINK V2 (and its various clones) are what OpenOCD calls a "high-level adapter." What does that mean?
The ST-LINK V2 is basically an ST Micro ARM chip running some special firmware which is designed specifically for programming/debugging ARM chips that support the Serial Wire Debug (SWD) interface and protocol. (SWD is a variant of JTAG that uses fewer pins.) The firmware accepts commands from a host computer via USB and then issues the corresponding SWD transactions to the device under test.
By contrast, you have things like the Olimex ARM-OCD-USB-H debugger which is considered a low-level adapter. This device contains an FTDI serial chip, which is basically a dumb device whose pins can be twiddled via host software. It doesn't know anything about SWD or JTAG protocols: the intelligence for that is all in the host software (in this case OpenOCD) and the software twiddles the pins to produce the correct signal patterns that correspond to the SWD transaction protocol.
The ST-LINK V2 is considered a high-level adapter because it accepts high-level commands from the host, and its functionality is limited by whatever the firmware developers decided to implement in it. The Olimex is a low-level debugger because you can basically do anything with it: it can support SWD, JTAG or custom protocols."
from: https://devzone.nordicsemi.com/f/nordic-...229#167229
"Regarding the protection bit, one thing to be aware of is that the ST-LINK V2 (and its various clones) are what OpenOCD calls a "high-level adapter." What does that mean?
The ST-LINK V2 is basically an ST Micro ARM chip running some special firmware which is designed specifically for programming/debugging ARM chips that support the Serial Wire Debug (SWD) interface and protocol. (SWD is a variant of JTAG that uses fewer pins.) The firmware accepts commands from a host computer via USB and then issues the corresponding SWD transactions to the device under test.
By contrast, you have things like the Olimex ARM-OCD-USB-H debugger which is considered a low-level adapter. This device contains an FTDI serial chip, which is basically a dumb device whose pins can be twiddled via host software. It doesn't know anything about SWD or JTAG protocols: the intelligence for that is all in the host software (in this case OpenOCD) and the software twiddles the pins to produce the correct signal patterns that correspond to the SWD transaction protocol.
The ST-LINK V2 is considered a high-level adapter because it accepts high-level commands from the host, and its functionality is limited by whatever the firmware developers decided to implement in it. The Olimex is a low-level debugger because you can basically do anything with it: it can support SWD, JTAG or custom protocols."
from: https://devzone.nordicsemi.com/f/nordic-...229#167229