https://devzone.nordicsemi.com/f/nordic-q-a/26066/spi-slave-race-conditionHi! After reading few posts about spi slave/master issues... I&#39;m also challenging with one of them. I have following setup nrf51822, s130 2.0.1 and sdk 12.3.0… nrf51 (spi slave) is communicating with arm cortex m3 (spi master) and I have establisheden-USTelligent Community 13Thu, 19 Oct 2017 08:50:45 GMThttps://devzone.nordicsemi.com/thread/102741?ContentTypeID=1Thu, 19 Oct 2017 08:50:45 GMT137ad170-7792-4731-bb38-c0d22fbe4515:fa1261f4-a0fe-455c-bbc8-e15c933a2ad3Sigurd<p>Hi,</p> <p>You can use <code>APP_PRIORITY_HIGH</code>(irq priority 1 on nRF51) as long as</p> <ol> <li>You are not making any SoftDevice calls from the high priority context.</li> <li>The callback is short so that it is not blocking UPPER STACK from executing.</li> </ol> <p>If you have <code>APP_PRIORITY_HIGH</code> in the SPI driver and have a lot of traffic with it, then you MIGHT notice lower throughput in the BLE stack because your SPI driver is blocking upper stack. It wont cause any faults and it is legal to use but you might see lower throughput. If that is not a problem in your usecase, and if you see that it solves your issues with SPI, it should be fine to use.</p><div style="clear:both;"></div>