How to reset a nRF52832 with only SWDIO and SWDCLK (not using a J-Link ruling out using "nrfjprog -p --family nrf52")

[Visti Andresen]

Hi

I'm currently trying to use a cheap stlinkv2 clone flashed with https://github.com/x893/CMSIS-DAP for at test setup.
(cmsis-dap enables it to remove APPROTECT/read back protection)

It works fine (currently only at half the speed of a "JLink Base"), but I would also like to be able to reset the chip to have the debug interface disabled.

For the nRF51 I have seen a description of a way to reset the chip:
https://devzone.nordicsemi.com/f/nordic-q-a/11/why-does-my-nrf51822-consume-1-ma-in-sleep

But as the nRF52 is different in this regard that method can't be applied.

As "nrfjprog -p --family nrf52" using a J-Link works (if done before a soft reboot which enables APPROTECT)
I know that it is possible to somehow reset the chip deep enough, that the debug interface is disabled using only SWDIO and SWDCLK.

So my question is: How does "nrfjprog -p --family nrf52" reset the chip?

Kind regards Visti Andresen

[Nguyen Hoan Hoang]

I power cycle will acheive the same result for enabling APPROTECT.  You can use OpenOCD for that too.  Reset using SWD is a debugger soft-reset command.  Alternatively the IDAP-Link CMSIS-DAP can also be used in place of the STLink. It is designed for handling nRF51 &nRF52. You can soft-reset with a press of a button or just issue a protect command which will both set the APPROTECT and reset.

[Visti Andresen]

Unfortunately the programmer is only connected using Vcc, GND (both not software controllable) and SWDIO and SWDCLK.

And while it would be possible for a human to disconnect power or push buttons a fully automated approach is desired.
(And possible since a JLink can pull it of, only the "protocol" eludes me)

[Kenneth]

Try nrfjprog --debugreset

[Nguyen Hoan Hoang]

The IDAP-Link does it fully automatic. It has software written specifically for parallel programming multiples boards for production purpose too. It handles programming of softdevice, app firmware and dfu with approtect activation.

[Visti Andresen]

But isn't nrfjprog limited to exclusively working with Segger j-link compatible interfaces?

Also as mentioned "nrfjprog -p --family nrf52" resets the chip deep enough to disable debug interface.

I would however like to know how "nrfjprog -p --family nrf52" performs the reset, which registers does it write to, does it send a bit stream to the nRF52?

As a side note writing 1 to CTRL-AP->RESET does reduce the idle current indicating that the debugger circuitry has been disabled, but the nRF52 seem to be stuck in reset/never reboots.
And I have to power cycle the device to regain control of it.

[Nguyen Hoan Hoang]

nrfjprog is for blink only.  IDAP-Link has its own IDAPnRFProg for it.

[Kenneth]

You may find this useful for additional information also:

https://infocenter.nordicsemi.com/topic/nwp_027/WP/nwp_027/intro.html