Can a code error prevent connection via SWD?

[Roger Clark]

Is it possible that a crash in code can prevent connection by SWD to an nRF51822?

As I had an instance this morning, where after uploading, some code to a smart watch, I could no longer connect via SWD, and had to disconnect and reconnect the power in order to reset the nRF51822 (the smart watch doesn't have an easily accessible reset connection)

I had tried disconnecting the SWD pins and reconnecting, and also unplugging the USB to the JLink, but neither of these actions seemed to allow connection.

Perhaps I should have tried pulling up the SWDIO pin a few times.

[Hung Bui]

Hi Roger, have you managed to do reset using SWDIO pin ? If the chip enter SYSTEMOFF you may have problem of accessing via SWD via interface.

You can use nrfjprog to trigger a pin reset (nrfjprog -p)

[Roger Clark]

Thanks @HungBui, the device i am programming is a fitness tracker bracelet and there is no access to the reset pin.

This problem has only happened once or twice, but its quite possible that the chip could have entered SYSTEMOFF by executing random code e.g. executing variables rather than code.

[Hung Bui]

Hi Roger, If you can access SWD via Jlink, means you can access reset pin, it's the same pin as the SWDIO pin, isn't it ?

nrfjprog -p will trigger the pin.