https://devzone.nordicsemi.com/f/nordic-q-a/16660/spi-issue-on-nrf52I&#39;m using nRF52+SDK11.0.0+S132 with an application based on the ble_hrs example. In main() , if I call a blocking nrf_drv_spi_transfer() to configure some SPI sensors before calling ble_advertising_start() , then my code spins in spi_xfer() &#39;s whileen-USTelligent Community 13Tue, 27 Sep 2016 00:14:30 GMThttps://devzone.nordicsemi.com/thread/63741?ContentTypeID=1Tue, 27 Sep 2016 00:14:30 GMT137ad170-7792-4731-bb38-c0d22fbe4515:aeebb079-6888-4150-a3d6-849da157bf1cTosa<p>It turns out that I was assigning P0.21 for SCK, which caused reset on the nRF52 DK (I&#39;m using the DK for code development before porting to custom hardware). So the following pins are fixed when using the nRF52 DK: // PCA10040 fixed pins: 32kHz 0, 1; UART: 5, 6, 7, 8; NFC 9, 10; BTN: 13, 14, 15, 16; LED: 17, 18, 19, 20; RESET: 21</p><div style="clear:both;"></div>