https://devzone.nordicsemi.com/f/nordic-q-a/1192/hardlock-issueChip: NRF51822 softstack version: 5.2.1 I ran into an issue and i&#39;m trying to understand it better. I was calling the function sd_ble_gatts_value_set(...) from a GPIOTE callback and the processor harlocked. Called from outside of the GPIOTE callbacken-USTelligent Community 13Thu, 02 Jan 2014 15:13:45 GMThttps://devzone.nordicsemi.com/thread/5558?ContentTypeID=1Thu, 02 Jan 2014 15:13:45 GMT137ad170-7792-4731-bb38-c0d22fbe4515:8de3c23e-722c-42eb-9e20-3302a1da1d66Ole Morten<p>Due to the way the softdevice works, you can&#39;t call softdevice API functions from interrupts with higer priority than the SVC handler (i.e. not from NRF_APP_PRIORITY_HIGH). You should therefore either lower the IRQ priority to NRF_APP_PRIORITY_LOW, or just do what you now do and always call this function from main context.</p> <p>This is explained in <a href="https://www.nordicsemi.com/eng/content/download/13233/212988/file/nRF51_Series_Reference_Manual_v2.1.pdf">the appendix of the nRF51 Reference Manual</a>.</p><div style="clear:both;"></div>