https://devzone.nordicsemi.com/f/nordic-q-a/122763/using-lesc-disrupts-system-interruptsHi there, In our device we are using nRF52832 with SoftDevice S112, SDK 17.0.1 and embOS Safe. Up until now we were working with the “Just Works” setting of BLE connection when using pairing through NFC. We recently tried upgrading to “LE Secure Connectionsen-USTelligent Community 13Mon, 07 Jul 2025 06:00:09 GMThttps://devzone.nordicsemi.com/thread/541554?ContentTypeID=1Mon, 07 Jul 2025 06:00:09 GMT137ad170-7792-4731-bb38-c0d22fbe4515:686bec83-4891-46a0-bafe-d728d2b688faSusheel Nuguru<p>When you switch to LE Secure Connections, Nordic’s S112 SoftDevice must do a full P-256 key exchange in software, which on the M4 takes about 20 ms and during that entire crypto operation it disables all interrupts using PRIMASK. From your RTOS’s viewpoint, your RTC tick interrupt simply never occurs for those 20 ms, so your software timers stop advancing and the watchdog trips. Raising the RTC’s NVIC priority won’t help, because PRIMASK blocks everything.</p> <p>The usual fix is to stop depending on interrupt-driven ticks for your time base. Instead, read a free-running counter (e.g. the raw RTC COUNTER register), or move your tick to a PPI+TIMER scheme that latches time without needing an IRQ, so that time still marches on even while SoftDevice is crunching its ECDH.</p><div style="clear:both;"></div>